• TABLE OF CONTENTS
HIDE
 Front Cover
 Advances in plant disease management...
 The need for an effective plant...
 Evaluation of potato cultivars...
 Evaluation of drenching triadimenol...
 Etiology of stem rot of ramie in...
 Variation in rhizoctonia solani...
 Identification of squash viruses...
 Note: Sources of resistance to...
 Abstracts of papers presented at...
 Information for contributors
 Back Cover














Group Title: Journal of Tropical Plant Pathology
Title: Journal of tropical plant pathology
ALL VOLUMES CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00090520/00030
 Material Information
Title: Journal of tropical plant pathology
Series Title: Journal of tropical plant pathology.
Alternate Title: Journal of Philippine phytopathology
Philippine phytopathology
Physical Description: v. : ill. (some col.) ; 26 cm.
Language: English
Creator: Philippine Phytopathological Society
Publisher: Philippine Phytopathological Society
Place of Publication: Philippines
College Laguna
Publication Date: January-June 1988
Frequency: semiannual
regular
 Subjects
Subject: Plant diseases -- Periodicals -- Philippines   ( lcsh )
Plants, Protection of -- Periodicals -- Philippines   ( lcsh )
Genre: periodical   ( marcgt )
 Notes
Dates or Sequential Designation: v. 1, no. 1 (January 1965)-
General Note: Title from cover.
General Note: "Official publication of the Tropical Plant Pathology."
 Record Information
Bibliographic ID: UF00090520
Volume ID: VID00030
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 54382605
issn - 0115-0804

Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Advances in plant disease management in the Philippines
        Page 1
        Page 2
        Page 3
        Page 4
    The need for an effective plant disease management in the Philippines
        Page 5
        Page 6
        Page 7
        Page 8
    Evaluation of potato cultivars for resistance to bacterial soft rot
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
    Evaluation of drenching triadimenol for efficacy against the black leaf streak and sigatoka diseases in giant cavendish banana
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
    Etiology of stem rot of ramie in the Philippines
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
    Variation in rhizoctonia solani kuhn causing sheath blight in sorghum
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
    Identification of squash viruses and screening for resistance
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
    Note: Sources of resistance to stem rot in ramie
        Page 53
        Page 54
        Page 55
        Page 56
    Abstracts of papers presented at the twenty-fifth annual meeting of the Philipine phytopathological society, Cebu City, May 3-7, 1988
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
    Information for contributors
        Page 72
    Back Cover
        Page 73
        Page 74
Full Text



r I I I


I


m











OFFICE

ROSALINDA P. GARCIA
AVELINO D. RAYMUNDO
MARINA P. NATURAL
CASIANA M. VERA CRUZ
JOSE M. BANDONG
CEFERINO A. BANIQUED
SAMUEL C. DALMACIO
ANACLETO N. PEDROSA,.
TWNG W. MEW
AGUSTIN N. PORDESIMO
TRICITA H. QUIMIO
OSCAR S. OPINA


PHILIPPINE I
EDITORIA

AVELINO D. RAYMUNDO
RIZALDO G. BAYOT
MYRNA Q. SEVILLA

CIRCULA
SILVII

SUSTAIN]

Berlime
Atlas Fe
Jard
Ciba4
Pione,
Shell Chei
Dow Cl
Aid
Mon
San M
BASF(
Rohm.
Transworld A
Rhone Poulen

Subscriptions: Communications should(
ment of Plant Pathology, UPLB, College, La
annually, is the official organ of the Philip
members in good standing and Sustaining Ass
$15.00 per copy elsewhere, postage free ar
Phytopathological Society Inc.: Information I
upon request. Page Charge: The editorial bo
amount for each published page commensurate
or supporting institutions. Advertisements:


L1UJ.L.JlIL 3ULI.-,1 I 11'N^.
iS 1987-88

* President
* Vice-President
* Secretary
* Treasurer
* Auditor
* Business Manager
* Board Member
* Board Member
* Board Member
* Board Member
* Board Member
* Immediate Past President
(Ex-Officio Member)

YTOPATHOLOGY
30ARD 1987-88

* Editor-in-Chief
* Associate Editor
* Associate Editor

3N MANAGER
D. MERCA

3 ASSOCIATES

hil. Corporation
izer Corporation
* Davies, Inc.
gy (Phil.) Inc.
Overseas Corp.
:al Co. (Phil.), Inc.
iical Pacific Ltd.
Corporation
tto Phil., Inc.
el Corporation
il.) Corporation
iaas (Phil.) Inc.
i Products Corporation
Lgrochemical Phil., Inc.

Addressed to the TREASURER, P.P.S. c/o Depart-
la 3720. Philippine Phytopathology, published semi-
e Phytopathological Society, Inc. It is sent free to
ates. For others, it is P50.00 per copy (domestic) and
payable in advance. Membership in the Philippine
Birding membership will be supplied by the Secretary
reserves the right to charge some authors a present
on the payment capabilities of their research projects
es may be secured from the Business Manager. No


^


"'~^"l"~t~"'~' "~ V~UC~'~









ADVANCES IN PLANT DISEASE MA


M. O.S

Keynote address of Session I during a sympos
ppine Phytopathological Society, Inc. held on Ma:
Former Head, Research Division, and Senior
m, Davao del Norte, Philippines


It is with great pleasure for me to be with
i on this occasion of the silver anniversary
the Philippine Phytopathological Society and
the nineteenth annual conference of the Pest
ntrol Council of the Philippines.
"Disease Management for Resource-Poor


LGEMENT IN THE PHILIPPINES


luan

i commemorating the 25th Anniversary of the
,1988 in Cebu City,Philippines.
nt Pathologist, Twin Rivers Research Center,



By exclusion we mean preventing the
:hogens by whatever means and methods
m entering and establishing themselves in
invaded areas. The Bureau of Plant Industry
th its Plant Quarantine Division has been
ked to intercept, eliminate, and prohibit the






2 Philippine Phytopathology VoL


even coconut buds for cooking from the Bicol fected soil is allowed to fallow for at least ni
Region where the cadang-cadang disease is months after all the banana regrowths hi
widespread; abaca and banana planting materials been eradicated. Fallowing will starve 1
from Davao where mosaic and bunchy-top are pathogen. So with crop protection.
presents citrus seedlings or propagative materials Root invaders or parasites in the soil are a
from Batangas where the tristeza disease was difficult and expensive to eradicate. There ;
rampant, etc. All these are precautionary mea- plant parasitic nematodes which can parasite
sures to safeguard the transfer of the pathogen and survive on a wide variety of plants inch
to healthy areas. ing weeds. The golden cyst nematode and otl
Philippine experience has shown that we species can now be controlled by Bioc
hoa- failarl in an a r nmir avrlllfannnrv nra-. (Palcilnmvces fiilncmis), a more econnmi


.. .. - . .. . . - . ..- .. . . .
golden cyst nematode (Globodera rostochie
sis) in white potatoes, the club root pathog
(Plasmodiophora brassicae) on crucifero
plants have been in the potato and vegetal
growing areas of Mt. Province, while the v
cular streak dieback of cacao (Oncobasidia
theobromae) is now well entrenched in t
Mindanao areas. The next strategy for th
control is to eradicate them.
By eradication, the infected plants have
be removed from the field to destroy t
pathogen. This may be true for any of t
diseases of our economic plants. However,
some instances only infected plant parts are
moved by pruning, such as with the mistletoe
infected branches of many fruit trees, I
vascular streak dieback, stem canker, and li
disease of cacao, etc.
Bacterial or vascularinfected tomato, pota
abaca and banana plants are completely era
cated. It has been a standard practice in lai
banana plantations to eradicate not only t
bacterialinfected plants but also all the health
buffer plants within the three meter radius.
the plants within this area are dug up, chopp
to pieces, and later fumigated, including the s(
with methyl bromide. Tools used for diggi
and chopping of the plants are later disinfect
with ten percent formaldehyde solution. T
disinfection will kill the bacterial pathogen
otherwise, they may be transferred from pla
to plant, or from place to place.
Backyard plantings of bananas that becof
infected by the bacterial wilt organism may
too impractical to fumigate. In this case t
most convenient and practical method wou
be to dig and chop all the buffer plants fir
and later the infected plant whose parts a
then placed in plastic sacks to decav. The i


the soil to starve the parasites takes a lo
period of time. The frequent cultivation, plain
ing of catch crops, crop rotation and ifpossil
planting of resistant varieties are the only
course left to take.
Plant viruses are somewhat difficult to cc
trol. The difficulty lies in the fact that some
them are not only mechanically transmitted b
also spread by insect vectors. This situation
one of the reasons for the change of the cro
now being grown in the Ilocos provinces. E:
dication practices may be three-pronged, nan
ly, the suscept, insect vector, and altema
hosts like weeds and other economic plants.
While it may be possible to eradicate t
suscept including the pathogen, there are i
stances wherein the farmer has to observe ott
control strategies. Crops that are continuous
grown in one area have to be protected frc
infection This protection starts from t
planting material like seeds, bulbs, tube
corms, and other vegetative plant parts. On
the plants have germinated they become si
ceptible to attack by organisms. This is al
true with tissue-cultured plants. The farr
then has to be alert in detecting all sorts
maladies that may appear on the leaves, sten
and roots so that immediate protection can
provided to the plants.
Protection for the plants is imposition
some effective barrier between the suscept a
the pathogen. This method is primarily direct
to the suscept when eradicatory measures ha
proven ineffective or when they become expe
sive.
In protection, we may manipulate the fi
tors conditioning infection and the applicati
of protectants. For example, many farmers p







In Plant Disease Managemen 3


ona wnat is normaly required. lTis condition
produces the favorable environment for infec-
ion. Thinning, provision of good drainage,
reaction of wind breaks, change of the soil pH
nd the change of temperature are factors that
manipulate the favorable conditions for infec-
ion.
Spacing or distance of planting is another
actor. Heavy tillers of rice should be spaced
differently from moderate tillers. The closer the
plants, the more they become susceptible to
ifection. In pineapples, spacing depends on the
purpose for which the fruits will be processed,
ii upon the dictates of the market for the fresh
ruit. Nevertheless, the closer they are, the
nore susceptible they become to heart rot or to
oot rot.
In banana plantations, the plants are usually
planted three meters apart, and later only three
plants are allowed for each hill. Higher densities
If planting, as in hedge rows or double hedge
ow, create a microclimate favorable to several
foliage diseases which require more protective
chemicals to protect the succeeding young
saves.
There are many chemical protectants now
available in the market for specific plant di-
eases. Regardless of their specificity, a farmer
rho intends to use any of these chemicals
should consider the following requisites:
1. It should either be fungicidal or fungi-
static.
2. They should not cause any burning of the
plant nor interfere with its physiological
or morphological development.
3. The chemical should not be toxic and
should be safe to handle.
4. Should not produce any undesirable
flavors and odors nor leave poisonous
properties on edible plant parts.
5. Should not be persistent in the soil.
6. Be compatible with other pesticides.
7. Should adhere or be tenacious on the
plant.
8. Easy to apply.
9. Non-corrosive to spraying equipment and
storage containers.
10. It should be inexpensive.

It would be very ideal if all these requisites
in be met. It seems that not one of the vesti-


des presently being used or those available
a the market meets all of these above requi-
tes.
A less expensive although tedious method of
protection a fruit grower practices nowadays, is
ie wrapping of mangoes, guava, jackfruit,
mpalaya, etc., with paper or plastic; so with
ie wrapping of fruits in storage and those
i transit with fungicide-impregnated paper to
prevent rotting. Other devices that may inter-
:re with the dissemination of plant pathogens
re in the form of direct barriers such as green-
ouses, windbreaks, and tall buildings. Al-
tough these are all expensive, they are not
s hazardous as chemical protectants.
Planing of resistant varieties is by far the
lost desirable method of plant disease control.
ice farmers here in the Philippines and those
F other rice growing countries have been plant-
ig many of the varieties resistant to blast,
rus diseases and other bacterial or fungal
athogens. All these varieties are the results of
painstaking work by plant breeders and plant
athologiests mostly from the International
ice Research Institute.
Crops or plant populations undergo selec-
on, hybrization, nutrition, medication, and
iccination. Selection involves merely the
etection of tolerant, resistant or immune
ants within a plant population and propaga-
ng them later through ordinary means or
rough the method of cloning as what is being
one or practiced in rust-resistant high yielding
)ffee varieties. This is also true with the Giant
avendish banana found to be resistant to the
isarium wilt organism and are presently multi-
led through the tissue culture method.
Hybrization involves the crossing of sus-
eptible but desirable plants with less desirable
it resistant sources. Although the method is
me-consuming, it has been relatively success-
11 in producing hybrids resistant to many
ithogens.
The nutrition of plants involves the use
Fertilizers or plant nutrients to correct ex-
sses or deficiencies, although its application is
united when it comes to pathogens.
Medication involves the introduction of
ibstances toxic to the pathogen within the
ant. It has very little prospect of being effect-
P and fnr oenrnal annuliratinn


In Plant Disease Managemen


3






Philiopine Phytopathology


V a%,ul.aLUvn Ju. J - --. -n m
mals, has very little prospect of its prac
ability though it offers interesting possil
lities.
The introduction of new varieties of annt
and perennial plants resistant or otherwise
some diseases, invariably takes along oth
plant pathogens that may cause other disea
problems many of us have not observed befoi
The presence of the pathogens may be ol
cured at first, but may appear a few years lati
This was true with the golden cyst nematoc
the club root of crucifers, and the vascul
streak dieback of cacao. It is just hoped th
the apple scab fungus may not find its way in
the apple growing areas, the black or stem ru
and leaf rust into the wheat areas of the Ioc


LU-- A bVa.^ **
ti-
With the foregoing enumeration of pla
i-
disease control practices and the examples
al disease occurrences probably unknown to sor
of us, the farmer has all the options to sele
e the practices applicable to his farming system
se without necessarily ending up with a big dr
from his pocket. What is important is to di
nose the plant disease accurately and apl
the appropriate control measure to save t]
e, crop.
ar Whetzel, a renowned plant pathologist on
it said, "For what will it benefit mankind if
:o the ills and diseases of the human race
st banished and yet face starvation due to t
)s diseases and pests in our food plants?"


A


__ _





IN THE PH]

R. G. I



Keynote address of Session 2 during a symposium
hilippine Phytopathological Society, Inc., held on
Associate Dean and Professor of Plant Patholog3
lines at Los Baflos, College, Laguna, Philippines.


Fellow Members of the Philippine Phytopa-
)logical Society, Ladies and Gentlemen:
It is indeed an honor and a rare privilege for
to be given the opportunity to deliver one
the symposium papers to mark the 25th
liversary of our Society, the Philippine Phy-
>athological Society, Incorporated. Speci-
ally, I am assigned to give an address on


PINES

ide



commemoratingg the 25th Anniversary of the
y 7, 1988 in Cebu City, Philippines.
)Ilege of Agriculture, University of the Philip-



still wanting or lacking. This may also indi-
e lack of technology transfer to and utiliza-
n by our farmers of the many known control
!asures that our plant pathologists have al-
dy developed. For instance, a few weeks ago
ny of us have probably read a news report in
; Manila Bulletin under the headline "First
nmercial wheat harvest ruined by fungus."






6 Philippine Phytopathology VoL


Ilocos region were seriously damaged by the campaign will be successful; if it fails our blool
mosaic disease. Dr. Santiago Obien, formerly ing banana industry may collapse or become
Director of the Philippine Tobacco Research sagging industry.
and Training Center, in a report to the Depart- likewise in the abaca industry, for mc
ment of Agriculture Secretary Carlos Domin- than 40 years now, we have been losing
guez "attributed the destruction of the tobacco much due to the attack of abaca mosaic a
plants to any of the following viruses; cucum- bunchy-top diseases. I understand the curre
ber mosaic, tobacco, potato, leaf curl of wild
cucumber." 1he most likely culprit is the administration is embarking on a progr
cucumber, mosaic virus, he said. On the other worth millions of pesos to develop virus-fr
hand, the National Tobacco Administration abaca seedlings through tissue culture to rel
(NTA) suspected that the use of adulterated bilitate the abaca industry in the Bicol regic
fertilizers could have indirectly influenced the Still in the Bicol region, the Cadang-cala
outbreak of the disease. This angle is now being disease of coconut which was the most d
investigated by the agency's evaluation team. I tructive disease in the 1950's and '60's, wh(


quaiuea ana expenencea tobacco plant paun
logists. Personally, I am more inclined to t
lieve that the recent massive growing of toma
and the introduction of potato growing in tl
region aside from tobacco could have a dire
effect on the build up of the insect vectors
the mosaic virus. In addition, the farmers their
selves who are directly handling these cro
could easily transmit the virus, mechanical]
I am suggesting therefore that our tobac
pathologists should consider these possibility
in studying the spread of the disease.
Another virus disease that we have not dol
much to control is the ring spot virus
papaya that practically wiped out the papa:
industry in 1984 in Cavite especially in Silan
area where 200 hectares were initially affect,
with a yield loss of $300,000. According
Dr. Oscar S. Opina of the Department of Pla
Pathology, UP Los Bafios, the virus is transm
ted by four species of aphids. Because of tl
lack of research funds it is unfortunate that E
Opina could not continue his study to develk
effective control measures against. the disease
Now the disease has already spread to oth
provinces particularly in Laguna, Batangas ai
Quezon. If not properly controlled, the disea
could destroy'our papaya industry.
Still another virus disease that is now threat
ening our banana industry in Mindanao is tl
bunchy-top which is seriously attacking n(
only the Cavendish variety but also many (
our native varieties such as saba, lakatan, bi
ngulan and others. Banana companies in Dava
are now joining hands with the government an
the farmers to eradicate the infected plants an
prevent the spread of the disease. I hope th


etiology and control, is still a problem,
though the cause is now known as viroids a:
the disease can be easily detected.
Outside the Bicol region, our coconuts
being threatened by a number of disea
against which we have not done much in ten
of control. Today the most destructive disc
of coconut whose cause is still unknown, is t
"Socorro wilt' occurring mainly in the muni
pality of Socorro, Oriental Mindoro, hence t
name. Since 1977 the disease has already d
troyed 24,000 hectares of coconuts. Unfi
tunately, unlike the Cadang-cadang disea
there is no continuous research support
study the cause and control of the disea
There is a minor disease of coconut whi
we have known during our student days and
is now becoming a major problem on new
developed coconut hybrids particularly on t
imported Mawa hybrid from Ivory Coast. T
is the stem bleeding disease. It is seriously
fecting the hybrids grown in PCA farms
Zamboanga and Davao. The coconut indusl
would have suffered so much had the gove:
ment not stop the importation of. Mawa I
brids in 1979. The exact cause of the disease
still not known although there are indicatic
that this may be caused by a fungus. In ad
tion, these hybrids are also susceptible to t
bud rot and leaf spot diseases. I hope our g(
emment will not insist on using these disea
susceptible hybrids for the replanting program
Otherwise, we will have more disease problem
which could result to more losses than wh
using our own native varieties.
We are still giving more attention and su






d For An Effective Plant Dis 7


)rt to the study of the rice and corn diseases
st like during the Marcos administration.
being our staple crops, rice and corn must be
own successfully in our land and at all cost.
ur plant pathologists especially those at
IRI have contributed a lot in the study of rice
seases and their control. However, tungro is
ill the most destructive disease on rice. In
>m, the downy mildew disease was well stu-
ed by Dr. Ofelio R. Exconde and his staff at
Le UPLB Plant Pathology Department and
)w it can easily be controlled by seed treat-
ent with the fungicide Ridomil. Despite these
gnificant advances in rice and cor pathology,
ir farmers still have some losses due to pests
Id diseases mainly due to the failure to apply
fective control measures.
Because we focused so much attention and
ipport on rice and corn diseases, disease prqb-
ms on many of our economic crops have prac-
,ally remained unsolved. For instance, in vege-
ble crops, the bacterial wilt of tomato, egg-
ant and pepper has remained a limiting factor
maximum production of these crops. Like-
ise, the fusarium wilt and bacterial wilt
seases are becoming more of a problem on
mana particularly on the Cavendish variety
Ad also in tobacco and other crops. Many fruit,
iliage and root rot and bulb rot diseases on
any crops are still not being effectively con-
)lled mainly because our farmers fail to
Oply adequate control measure before the
sease becomes severe.
On the diseases caused by nematodes such as
ot knot, root rot, stubby root, root lesions
id others, there are still no adequate control
measures available. The nematicides for nema-
de control are only available for the use of
antation companies where laborers are given
equate medical attention. Being a first class
oison to man and animals, nematicides are
stricted for use by individual farmers in this
untry. However, our recent discovery of
me soil fungi, particularly Paecilomyces lila-
zus, which are highly effective against most
ant parasitic nematodes, presents a bright pro-
ise that biological control of nematodes can
effectively and safely used by the farmers. If
)t adequately controlled, nematodes can cause
serious problem in crop production. For


stance, in Cavendish banana in Davao, despite
- application of nematicides, banana compa-
es still suffer substantial losses due to blow
wn or tip-over due to weak root system re-
Iting from infection by nematodes Radopho-
s similis and other species. Blow-down is
ought about by sudden occurrence of a
ong wind. Two weeks ago, I was at the Mars-
m Banana Plantation in Davao and I saw the
struction of 56,000 plants equivalent to 29
ctares of banana. Similar or even higher blow-
iwn damage which could reach a thousand
ctares has been reported in other banana
stations. This means that the nematode
ntrol is still inadequate. We hope our fungal
)control can reduce the damage in the future.
Although the science of plant pathology.has
eatly advanced during the last 25 years, appa-
ntly not much has been done in the applica-
)n and utilization of developed disease con.
)1 technologies at farmer's fields. Either
e technology has not reached the end-user or
is just not practical to use. It appears that it
in the transfer of new knowledge that we
ally bog down because of lack of financial
pport. I hope the Society can find means to
nedy this situation.
The scenario of disease problems in the next
to 20 years may be entirely different from
Last 25 years. With the full implementation
the land reform program, the country, may
ve more lands under cultivation and as our
man population increases, this will definitely
iult in the intensification of food production.
cause of the demand for more food, our
ople may be introducing more high yielding
brids of various food crops which are suscep-
le to different diseases. Most likely, many
nor diseases today may become major prob-
ns on these new hybrids in the long run.
Furthermore, there may be more forest
Ids destroyed by loggers and kaingeros up-
ting the ecological balance between the
thogens and beneficial microorganisms and
ich could favor the former. With the intro-
ction of more susceptible crops in these
mas, there will be more disease problems
rich we may not be able to control effectively.
In the coming years the society will indeed
ve a great opportunity to meet the challenge
more disease outbreaks affecting our crops.
us, it must prepare to respond positively to


d For An Effective Plant Disl


7







2 Phlppn PhyopthooI


e times and act as the vanguard more effective disease management in thu


[try. The PPS must take the lead role in the professional responsibility to see
voting research and extension services in knowledge gained through research
t pathology. To prepare for this role, the lopment are transferred and gainfull
ty must intensify its recruitment of young by the end-users. We are here to e
bright students to major in plant pathology health of our food crops. If our crops
fferine them more scholarships, still being destroyed subtantiallv by


kewise, the :
in the forr
nt introduce
s. Our quarai
illy and mus
'e all, the so,
irmulating g
tive manager
0 this, we cai
ig our plant ]
closing, I
a pivotal ro


assist 1
)und
disea
t be i
I by t
ve a si
)licies
dises
effecti
robler
ety v
camp,


t
t
s
i:
r
t
I
i




1


iat we
hope
ievemi
)pmen
1 to ii
done
SLet 1
the S
order
ang
ppy ai
ank yo


R


Phirivvine Phvtovatholmrv










EVALUATION OF POTATO CI
TO BACTERL

Lucia M. Borines, Marina P. P


Portion of MS thesis of the Senior Author s
mnos (UPLB).
Respectively, Instructor, Dept. of Crop Pr
tybay, Leyte; Assistant Professor, Dept. of Plar
iuos; Regional Director, International Potato (
office, PCARRD Complex, Los Banos, Laguna, Phi


ABSTI

Three inoculation methods were compared for
their effectiveness in evaluating for soft rot resist-
ance in potato tubers. Dipping the tubers in bacter-
ial suspension for one hour was found to be the
best method resulting in 83% tuber soft rotting
after 7 days of inoculation. Based on the number
of tubers infected and soft rot lesion diameter, no
difference was observed whether tubers were


TIVARS FOR RESISTANCE
I SOFT ROT

tural and P. Vander Zaag


mitted to University of the Philippines at Los

action, Visayas State College of Agriculture,
Pathology, University of the Philippines, Los
iter, Far East and Southeast Asia Regional
,pines.


CT

control tubers.
The 40 and 11 cultivars in the first and second
latches, respectively, showed significantly differ-
nt levels of disease in terms of number of tubers
infected and lesion diameter. Cruza 148, BR
i3.74,378597.1 and BL -2.9 were considered re-
istant while F79002, F79021 and Kennebec were


both conditions of inoculated tubers resulted in lated to softrot resistance. Cultivars with higher
significantly higher infections and larger diameter calcium content were found to be more resistant to
of soft rot lesions as compared with uninoculated the disease.


INTRODUCTION
to soft rot in tht Philippines has not beer
Advancement in the agrotechnology ofe undertaken in the past. One reason could be the
>tato production in the Philippines has lack of a reliable inoculation technique to
potato production in the Philippines has
iticed farmers to produce this crop for local properly evaluate resistance. Another reason
mnsumption. Mass production of potato, how- could be the pre-conceived notion that resist-
er, is still insignificant to ensure a steady sup- ance is not available against storage diseases
y of potatoes in the market. High losses are like soft rot because Erwinia spp. could attack
curred after potatoes arg harvested in the a wide range of hosts that no potato cultivar
:ld. These postharvest losses occur either in can withstand the effects of these bacteria.
ansit or in storage caused by pests, diseases and This study was therefore conducted to dev-
iproper handling and storage. One of the elop a technique of screening potato cultivars
ost serious postharvest problems is bacterial for soft rot resistance in storage, evaluate resist-
ft rot caused by Erwinia species. The patho- ance of cultivars maintained at the International
ns associated with the disease are Erwinia Potato Center (CIP), Los Banos, Laguna, and
rotovora pv. carotovora, E.C. pv. atroseptica correlate calcium content and resistance of
id E. chrysanthemi. Erwinia carotovora pv. potato tubers to bacterial soft rot. Except for
rotovora is widely distributed and is the most calcium content analysis, all experiments were
mmon soft rot organism. In general terms, conducted in the Plant Pathology laboratory,
C. pv. atroseptica may be regarded as a cool CIP Regional Germplasm and Training Center
mperature variant of pv. carotovora, restrict- at Mt. Banahaw, Dolores, Quezon from October
largely to potatoes, It causes also the black- 1985 to June 1986. Calcium content of tubers


Rcreenina of potato cultivarm fo reqlatdnce







Philippine Phytopathology Vol. 24.


MATERIALS AND METHODS

Test Cultivais

Two batches of cultivars were screened for
resistance to bacterial soft rot. The first batch
of tubers composed of 40 cultivars were har-
vested in Canlubang, Laguna while the second
batch of 11 cultivars were harvested in Mt.
Banahaw, Sta. Lucia, Quezon. They were
stored under diffused light in Sta. Lucia,
Quezon until being used for the experiments.
Tubers that were relatively free from skin in-
juries were selected, washed in running tap
water and soaked in 2.5% calcium hypochlorite
for 15 min to remove surface contaminants.

Test Isolates

Isolates of Erwinia carotovora were freshly
isolated from tubers showing bacterial soft rot
to ensure their virulence. The isolated bacteria
were inoculated to healthy tubers and reisolat-
ed from tubers that were severely Pliseased.
These isolates served as stock cultures for
subsequent screening work.

Comparison of Inoculation Methods

Three methods of inoculating Erwinia caro-
tovora, namely: injection, drop and dip methods
were compared. In .each inoculation method
twelve tubers of Russet Burbank, a known
susceptible cultivar, were used to compared the
efficiency of the inoculation methods. Bacterial
inoculum was standardized at 109 colony
forming units (CFU) per ml with the use of a
spectrophotometer. In the injection method,
0.1 ml bacterial suspension was injected into
tubers to a depth of 1 cm. In the drop method,
a hole about 3 mm deep was made in each
tuber using a 6 mm dia cork borer and the hole
was filled with bacterial suspension. In the dip
method, a hole was similarly prepared as in the
drop method and the holed or wounded tubers
were dipped into a bacterial suspension for one
hour.
The inoculated tubers were placed inside 10
x 28 cm plastic bags, laid in trays and incubated
under room temperature. The number of in-
fected tubers were recorded at 3, 4 and 5 days
after inoculation (DAI). The method that gave


the highest number of infection was used in the
actual evaluation of potato cultivars for resist-
ance against soft rot.

Screening for Soft Rot Resistance

The experiment was laid out in a split plot
design with three replicates. There were three
main plots to represent the condition of tubers,
namely: inoculated intact, inoculated wounded
and uninoculated control. Each main plot
had 40 subplots in the first batch and 11 sub-
plots in the second batch of tubers representing
the cultivars that were screened for resistance.
Six tubers per replicate per treatment were
used.
Inoculation was done by dipping the intact
and wounded tubers in bacterial suspension for
one hour. Uninocualted control tubers were
dipped for one hour in sterile rain water.
Bacterial inoculum was prepared by suspending
48 hour old bacteria, grown on potato dextrose
peptone agar (PDPA), in sterile rain water and
standardized to about 109 CFU/ml. After
dipping, the tubers were drained, the cultivars
kept separately in plastic bags and arranged in
trays. They were placed in a big wire shelf at
room temperature for incubation.
The number of infected tubers and diameter
of lesions were recorded at 3, 4 and 7 days
after inoculation. From the data on lesion
diameter, the rate of increase in lesion diameter
was computed.

Calcium Analysis of Tubers

Tuber samples from representative cultivars
used in soft rot screening were analyzed for
calcium content and was correlated to resist-
ance of cultivars to soft rot.
Ten tubers per sample were sliced into 1 mm
thickness. These were oven dried for 3 days at
80 C in paper bags, ground in Wiley Mill and
oven dried again for 1 day. One gram per
sample was placed in a crucible and ashed in a
muffle furnace. They were heated for 2 hours
at 80 C. The ash was mixed in 10 ml water and
another 10 ml was used to rinse the crucible
making a total of 20 ml suspension. Calcium
content in parts per million was determined
using atomic absorption based on prepared
standards.


Philippine Phytopathology


Vol. 24







ian. a June i~ea L.vaau.uuII Un ruts.,, tutu,...


LTS AND DISCUSSION change through me lenucels and the itemal
tissues were under oxygen stress (Burton and


are very susceptible to soft rot bacteria as well
Preliminary tests to determine the best ino- as to the pectolytic enzymes they excrete
PrelimiA naA Utests to d'etem. the best J1 f.A-l+I"-


ior resistance


I - /-
section method, v
tuber infection 3,
tion, respectively.
the tubers inoculat
The injection a
ion resulted in kl
pectively, because
were exposed to
unount of bacter
points of inoculat
method of inocul;
tuber infection be
nletelv surrounded


itato cuiuvars ..,
ift rot showed 1983; Bartz and Kelman, 1984a).
-ft ro showed 1 --


itroge.
n str(
id Ke.
iese i
Id to 1
The
our
e mc
timber
period ,
imber
'ft rot


method


e usec
Lind(
Bour
t alw;
ling.
oculal
ecauso
qr less
be inc
deal f
rPQiei


have access to suitable entry points. Further- Resistance to Soft Rot
more, a low oxygen tension was created on the Three different parameters were used in
dipped tubers because they were not air dried evaluating resistance of potato cultivars to Er-
before placing in plastic bags such that a conti- winia carotovora causing soft rot. These were 1)
nuous film of the suspension covered the tuber average number of tubers infected, 2) average
surface for an extended period of time. This lesion diameter, and 3) rate of increase in lesion
water fPm- prevented adequal oxygen ex- diameter with time (b).


Table 1. Percentage tubers infected with Erwinia carotovora using three inoculation methods at 3,
4 and 5 days after inoculation of the vathoeen


INOCULATION
METHOD



Injection

Drop

Dip


1 Based on the average of 12 tubers per treatment.


PERCENT TUBER INFECTION'

Days After Inoculation

3 4 5


8.3 16.7 16.7

0 0 0

0.0 60.0 83.0


#an. t June I uS


jmuiuuuiL ui rUomtu .UIuvia







hilippine Phytopathology


Table 2 shows the average number of tubers
infected with soft rot in the first batch of cul-
tivars evaluated at 3, 4 and 7 days after inocula-
tion. The data are average of intact and wound-
ed tubers using 6 tubers per replicate per treat-
ment. The treatment means were compared
using the least significant difference (LSD) at


ant, moderately susceptible and susceptible
based on the number of infected tubers 7 days
after inoculation. Three cultivars, BR 63.74,
378597.1 and BL-2.9, fall under the resistant
category (Table 2). Eleven cultivars such as P-3,
Cosima, F79101, etc., were considered moder-
ately resistant. Examples of moderately sus-


The 40 cultivars showed significantly dif- Red Pontiac. F79002, F79021 and Kennebec
ferent levels of disease in terms of number of fall under the susceptible category.
tubers infected at 7 days after inoculation. The The soft rot lesion diameter in each cultivar
cultivars were grouped arbitrarily into four and the computed rate of increase in lesion
categories, namely; resistant, moderately resist- diameter are shown in Table 3. Using these two

Table 2. Number of tubers infected with Erwinia carotovora in the first batch of potato cultivars it
intact and wounded tubers observed at different time intervals


NUMBER OF TUBERS INFECTED1

CULTIVARS Days After Inoculation
3 4 7

BR 63.74 2.3 2.5 2.8
378597.1 2.5 2.5 2.8
BL-2.9 2.3 2.8 3.0

P-3 2.0 3.3 3.5
Cosima 2.5 3.0 3.3
F79101 2.5 3.3 3.5
F79070 2.5 3.3 3.3
382053.11 2.8 3.0 3.5
LT-1 2.3 3.0 3.3
LT-5 2.3 3.0 3.3
ASN 69.1 2.5 3.3 3.8
LT-2 1.8 2.8 3.3
F79060 2.0 3.3 3.8
F79072 2.8 3.3 4.0

A. Russet 3.0 3.8 4.5
DTO 28 3.3 3.8 4.8
R. Pontiac 3.5 4.0 4.3
MS-IC-2 3.0 3.5 4.5
CGN69-1 4.0 4.3 4.8
Sequoia 4.3 4.8 5.0
Raritan 3.3 3.5 5.0
67015-11RY 3.8 4.0 4.5
Fundy 4.3 5.0 5.3
F79078 4.5 4.8 5.0
Jeniseg 4.5 4.8 5.0
Spunta 3.8 4.5 5.5
65-ZA-5 3.3 4.0 5.3
F79094 4.5 5.0 5.3
BR-69-84 4.3 4.8 5.3

Utatlan 3.8 4.5 5.5
F67128 4.5 4.5 5.3
R. Burbank 4.5 5.5 5.5
Wauseon 5.0 5.3 5.8
Desiree 3.8 4.8 5.8
F79055 4.5 5.3 6.0
F79092 4.5 5.3 5.5
Bintje 4.3 5.0 5.5
F79021 5.5 5.8 5.8
Kennebec 6.0 6.0 6.0
F79002 5.8 6.0 6.0

CV 37.5 27.7 2.0
LSD .05 1.8 1.6 1.5
.01 2.4 2.1 2.1


All+t nf f t 4,+nl +f-f h 4lli.j, .n __ m


VoL 24










Table 3. Soft rot lesion diameter of the different potato cultivars at different time interval
and rate of increase in lesion diameter with time (b)


LESION DIAMETER (mm)1
b2
CULTIVARS Days After Inoculation (mm/day)

3 4 7

BR 63.74 3.5 5.9 12.1 .09
BL-2.9 3.9 6.8 12.1 .09
378597.1 6.8 9.8 15.1 .09
P-3 3.2 6.8 13.3 .11
382053.11 4.0 6.9 13.4 .10
Cosima 5.8 9.9 16.7 .12
LT-5 4.6 8.1 15.2 .12
ASN 69.1 4.8 9.7 17.6 .13
F79101 5.3 9.4 18.8 .14
F79072 6.3 10.8 19.5 .15
LT-2 4.3 9.9 19.2 .15
F79060 5.1 11.6 23.4 .18
LT-1 4.1 8.7 20.5 .16
F79070 5.3 12.5 22.8 .18
MS-IC-2 6.6 12.4 22.6 .18
67015011RY 8.8 14.9 26.6 .19
R Pontiac 10.6 19.3 29.5 .21
A. Russet 7.0 15.1 30.3 .24
CGN69-1 10.9 18.3 31.3 .23
Spunta 9.5 17.1 33.5 .24
65-ZA-5 6.1 12.7 29.2 .23
DTO 28 10.6 17.0 31.0 .23
Raritan 9.4 17.7 35.3 .27
Jemseg 11.3 20.7 37.1 .28
F79078 13.8 23.9 39.2 .28
Sequoia 13.5 23.9 38.9 .28
F79092 14.1 23.7 37.8 .27
Wauseon 17.1 28.3 41.2 .28
Utatlan 8.7 17.1 36.6 .29
F67128 15.1 24.1 39.9 .16
Desiree 9.9 18.1 39.7 .30
F79055 11.3 24.4 42.0 .32
F79094 15.1 27.0 41.9 .30
R Burbank 14.2 26.9 45.1 .34
Bintje 12.5 23.8 41.25 .30
F79021 18.9 34.4 48.3 .33
Fundy 9.4 21.1 43.6 .35
BR-69-84 11.6 26.2 45.6 .35
F79002 18.5 32.5 47.6 .34


CV 56.0

LSD .05 7.6
.01 10


Computed from the averages a
2b= Rate of increase in lesion
= a + b X where Y represent the slope of the linear r
and time (days after incubation independent variable).


39.9 28.3 26.4

9.9 12.2
13.0 16.1


ubers per replicate per treatment.
eter computed from the simple linear regression formula Y
ssion between lesion diameter values (dependent variable)


Evaluation of Potato rultivars


Jan. & June 1981






doL 24


hilippine Phytopathology


parameters, cultivars BR 63.74, BL-2.9,
378597.1, P-3 and 382053.11 are considered
resistant witt lesion diameterranging from 8.0 to
10.1 mm 7 days after inoculation. The suscep-
tible cultivars, F79021, BR-69.84, F79002 and
Kennebec had lesion dimaters ranging from 32.0
to 44.0 mm. As expected, the rate of increase
in lesion diameter was much slower in the
resistant cultivars (b = 0.09-0.10 mm/day) as
comparedd to the susceptible ones (b = 0.3 -
).41 mm/day).
Results of the evaluation of the second set
of cultivars are shown in Tables 4 and 5. Based
on the number of tubers infected at 7 days
after inoculation, only Cruza 148 exhibited
resistance to the disease (Table 4). Using lesion
diameter and rate of increase in lesion diameter
as parameters, however, three more cultivars
had significantly lower levels of disease. They
were 1-1062, P55.7 and GLKS 58-1642.4.
Tl'h main 1-ille rf thpe ultivarc Pvalnated


ivars or
Durir
nean m
anged f
while m
: to 2c
ind soil
through
tubers \
atent s4
highest
-uarv (!


lubang, Laguna. Most of the cul-
d from Agriculture Canada.
growing period of these cultivars,
m air temperatures in Canlubang
8.7 in January to 21.6 C in March
m temperatures ranged from 27.7
Rainfall which enhances blackleg
infection in the field was minimal
ie growing period such that the
assumed to be relatively free from
: infection. Relative humidity was
,-1- i.t0\ --nA in...1frt in V.'k


ine expenment was conaucreu at nme ran
'athology laboratory at CIP's Regional Germ-
alasm and Training Center at Mt. Banahaw,
Dolores, Quezon. The experiment site is at mid-
elevation (800 m ASL). The temperature was
generally low or cool during the night and
^ -A- +- +/ia *rvin A th ..4 +1- l A n m-ini1


Table 4. Number of tubers in the second set of cultivars infected with Erwinia carotovora in
intact and wounded tubers observed at different time intervals

NUMBER OF TUBERS INFECTED1

CULTIVAR Days After Inoculation

3 4 7


Cruza 148 1.5 2.2 2.3
BR 63.76 1.8 3.2 3.8
CFS 69.1 2.8 3.5 3.8
GLKS-58-1642.4 2.8 3.7 3.8
P-55.7 2.2 3.5 4.0
1-1062 2.5 3.5 4.0
MS-35-9 3.0 3.7 4.0
1-931 2.3 3.3 4.2
DTO 2 3.2 3.7 4.5
BR 63.15 3.5 4.2 4.5
6947-2 4.0 4.3 5.2

CV 50.3 28.8 19.7

LSD .05 1.5 1.1 0.8
.01 1.9 1.5 1.1


10ut of a total of 6 tubers per replicate per treatment.







Jan. & June 1988 Evaluation of Potato Cultivars


Soft rot lesion diameter in the second set of cultivars at different time intervals and
rate of increase in lesion diameter with time (b)


LESION DIAMETER (mm)1


Days After Inoculation
-------------------------------


CULTIVAR


Cruza 148
1-1062
P-55.7
GLKS 58-1642.4
BR 63.76
MS-35-9
CFS 69.1
BR 63.15
1-931
DTO 2
69-47-2


3.7
7.5
7.1
7.8
7.1
8.4
7.6
10.8
8.8
9.4
13.5


8.1
16.7
16.8
17.6
18.5
19.0
20.7
22.5
23.6


CV 58.6 44.9 30.4 30.2


LSD .05 2.9 4.1 6.6 .04
.01 3.9 5.4 8.7 .06


IComputed from the averages of 6 tubers per replicate per treatment.
b= rate of increase in lesion diameter computed from the simple linear regression formula Y =
a + b X where Y represents the slope of the linear regression between lesion diameter values (dependent variables)
and time (days after incubation independent variable).


October to 19.8 C in June, while maximum was
from 27.9 C to 30.5 C. The relait.e humidity
was generally high or approaching saturation
because of its location in the mountain. In
other words, the environmental conditions
during the conduct of the study were favorable
for soft rot development.
Some cultivars, although found resistant to
soft rot were not good in terms of adaptability
under our condition and in terms of yield.
The cultivar found most resistant to soft rot was
BR 63.74, but it was not adapted under Philip-
pine conditions (Pangilinan, et al., 1985) be-
cause the tubers exhibited heat stress symptoms
and were very small which made them unac-


ceptable to consumers. F79101 showed mode-
rate resistance to soft rot but was also poor in
terms of yield.
Cosima; LT-2, LT-5, LT-1 and F79070 are
good examples of high yielding cultivars with
moderate resistance to soft rot. High yielding
cultivars such: as CGN69-1, Spunta and Red
Pontiac were moderately susceptible to soft rot.
Desiree and F79055, on the other hand, are
examples of high yielding varieties which were
found susceptible to soft rot.
Using the three parameters to evaluate the
difference between the mainplot treatments, it
was observed that the level of disease in the
inoculated tubers (wounded and intact) was


Table 5.


b2
(mm/day)


Jan. & June 1988


Evaluation of Potato Cultivars







Philippine Phytopathology VoL 24


significantly different from the uninoculated
tubers (control) (Tables 6, 7, 8 and 9). In the
first set of cultivars, there was no significant
difference in the number of tubers infected,
lesion diameter and rate of increase in lesion
diameter between the intact and wounded
.ubers (Tables 6 and 7). Unlike the first set, the


second set of cultivars had a different result.
There were significant differences in the num-
ber of tubers infected, lesion diameter and rate
of increase in lesion diameter with time, be-
tween the intact and the wounded tubers
/Tables 8 and 9).
The second set of cultivars or the Sta. Lucia


Table 6. Number of intact, wounded and control tubers infected with Erwinia carotovora
at different time intervals


'NUMBER OF TUBERS INFECTED'
MAINPLOT
TREATMENT 3 4 7

Wounded 4.4 a2 4.8 a 5.0 a
Intact 4.7 ab 3.4 ab 4.1 ab
Control 0.3 c 0.6 c 0.7 c



1Average of 6 tubers per replicate per treatment.
2Any two means within a column having a common letter are not significantly different from
each other using DMRT at the 5% level of significance.



Table 7. Soft rot lesion diameter in each mainplot treatment at different time intervals and
rate of increase in lesion diameter (b)


LESION DIAMETER (mm)1
b
MAINPLOT Days After Inoculation (mm/day)
TREATMENT
3 4 7


Wounded 12.5 a2 21.8 a. 35.5 a .26 a


Intact 7.1 ab 13.8 ab 25.3 ab .19 ab


Control 0.7 c 1.8 c 3.4 c .03 c


CV 52.3 47.1 14.2 18.3


1Averages of 6 tubers per replicate per treatment.
2 Any two means within a column having a common letter are not significantly different from
each other using DMRT at the 5% level of significance.


Philippine Phytopathology


VoL 24














NUMBMK Uk TUBES INFECTED'

Days After Inoculation

4 7

a2 5.2 a 5.5 a


b 1.9 b 2.5 b


c 0 c 0 c

ment.
a common letter are not significantly different from




ot treatment (second set) at different time inter-
er (b)


Jan....... ..... .. . of P t i


. naJ & June 1988


Evaluation of ent~tn ~a~~~


and control tubers infeli


MAINPLOT

TREATMENT

Wounded 4


Intact 1


Control 0


Averages of 6 tubers per replicate per tj
Any two means within a column hav:
each other at the 5% level of significance.



Table 9. Soft rot lesion diameter in each maih
vals and rate of increase in lesion dian







Philippine Phytopathology VoL 24~


samples from these two areas also confirmed
that Canlubang soil has a lower calcium content
than Sta. Lucia soil. Thus calcium content of
soils from these two areas may also reflect the
calcium content of the cultivars harvested from
them and calcium content is said to affect sus-
ceptibility of tubers to soft rot.

Relationship Between Calcium Content
of Tubers and Resistance to Soft Rot

Calcium content of tubers was inversely
related to the rate of increase in lesion diameter
(Table 10 & Fig. 1). Cultivars with relatively
high calcium content like BL-2.9, 378597.1 and
BR-63.71 had the lowest rates of increase in
lesion diameter. A negative linear relationship
was obtained with a correlation coefficient of
0.758. This study provided additional proof
that calcium content plays a role in the resist-
ance of cultivars to soft rot.


0.22
0.20
0.18
0.16
0.14
(r)
0.12
0.10
0.08
0.06
0.04
0.02


Legend:
a-- regression line
Y 0.1985-0.0015X
ra-0.7584








^.


10 20 30 40 50 60 70 8o 90 00
Relative Calcium Contnt (ppm)

Fig. I. Relationship between calcium content
of tubers and resistance to soft rot in
terms of rate of increase in lesion
diameter (r)


Table 10. Relative calcium content of potato cultivars (ppm) and disease severity in terms of rate
of increase in soft rot lesion diameter (b)


RELATIVE CALCIUM CONTENT
CULTIVAR (ppm) (b)'


F67128 20.0 .16
F79078 20.0 .28
65-ZA-5 40.0 .23
DTO 28 60.0 .23
CGN69-1 20.0 .23
A. Russet 20.0 .23
Red Pontiac 20.0 .21
67015-11RY 40.0 .19
MS-IC-2 60.0 .18
F79070 60.0 .18
LT-1 60.0 .16
LT-2 60.0 .15
F79072 40.0 .15
F79101 60.0 .14
Cosima 80.0 .12
P-3 60.0 .11
378597.1 60.0 .09
BL-2.9 60.0 .09
BR-63.74 100.0 .09


1 Taken from the computed rate of increase in lesion diameter of the different cultivars (Table 3).


VoL 24,


Philippine Phytopathology






n. & June 1988 Evaluation of Potato Cultivars ,19



LITERATURE CITED



ARTZ, J.A. and A. KELMAN, 1984a. Inoculation of FRENCH, E.R. and L. DE LINDO. 1979. The Erwi-
potato tubers with Erwinia carotovora during simu- nias of potato in Peru. Pages 88-93 in: Develop-
lated commercial washing and fluming practices. ments in control of potato bacterial diseases. Re-
Am. Potato J. 61: 495-507. port of a planning conference. Int Potato Center,
Lima, Peru.
LRTZ, J.A. and A. KELMAN. 1984b. Bacterial soft
rot potential in washed potato tubers in relation to LUND, B.M. and G.M. WYATT. 1972. The effect of
temperatures of tubers and water during simulated oxygen and carbon chloride concentrations on


IURNE, W.F., D.C. MC CALMONT and R.L.
WASTIE. 1982. Assessing potato tubers for suscep-
tibility to bacterial soft rot ((Erwina carotovora
subsp. atroseptica). Potato Res. 24: 409-415.

RTON, W.G. and M.J. WIGGINTON. 1970. The
effect of a film of water upon the oxygen status
of potato tuber. Potato Res. 13: 180-186.

SBOER, SH. and A. KELMAN. 1978. Evaluation
of procedures for detection of pectolytic Erwinia
spp. on potato tubers. Am. Potato J. 52: 117-123.


Potato Res. 15: 174-179.

AHER, E.A. and A. KELMAN. 1983. Oxygen status
effects on maceration of potato tuber tissue by
pectin enzymes produced by Erwinia carotovora.
Phytopathology 73: 536-639.

LNGILINAN, I., P. VANDER ZAAG and A. DEMA-
GANTE. 1985. Potato (Solanum spp.) in an isohy-
perthermic environment of the Philippines; Germ-
plasm evaluation during the 1984-85 season.. The
Potato in Southeast Asia and the Pacific Region
Research Results Presented in a Series of Working
Papers. International Potato Center. 304 pp.





Philippine Phytopathological Society, Inc.
1988 Phil Phytopath. 24: 20 28


EVALUATION OF DRENCHING TRIADIMENOL FOR EFFICACY
AGAINST THE BLACK LEAF STREAK AND SIGATOKA
DISEASES IN GIANT CAVENDISH BANANA

M. O. San Juan and G. Atabug

Former Research Division Head and Associate Plant Pathologist, Twin Rivers Research Center
Madaum, Tagum, Davao del Norte.


ABSTRACT


Three rates of triadimenol (Bayfidan 250 EC)
were drenched unto the base of the mother plant
pseudostem at three application frequencies and
evaluated for efficacy in controlling the black leaf
streak and sigatoka disease in Giant Cavendish
banana. All the triadimenol treatments provided
significantly longer disease incubation and transi-
tion periods and more functional leaves per plant
than the untreated control. Application of triadi-



INTRODUCTION


Black leaf streak (BLS) caused by Mycos-
phaerella fijiensis Morelet and sigatoka disease
caused by Mycosphaerella musicola Leach are
the most important leaf diseases of triploid
AAA types of banana in the Philippines. Black
leaf streak symptoms on the leaves are initially
small, barely visible yellow or brown specks
which soon turn into brownish-black streaks.
The streaks later become elliptical spotshaving
a brown margin, gray center and yellow halo.
Excessive leaf spotting hastens leaf senescence,
causes premature ripening of fruits (Stover,
1974) and reduces bunch weight (Leach, 1946).
Aerial spraying using fixed-wing aircraft is
the most convenient method of applying fungi-
cides with or without oil to control the BLS
and sigatoka diseases in large banana planta-
tions. In small fragmented farms, bananas are
sprayed with fungicides using tractor-mounted
turbine-driven sprayers. Both aerial and ground
spraying of fungicides generally provide ade-
quate control of the leaf diseases. However, the
high cost of fungicides and their application as
well as the continued existence of disease "hot
spots" in the plantation justify the search for
cheaper, more effective fungicides and alterna-
tive or complementary application methods.
SApplication of fungicides through the soil is
a simple method that does not require expen-
sive requirement. Only systemic fungicides that


menol at 1.0 g and 0.75 g active ingredient per mat
once every 2 and 3 months were most effective
against the disease with residual efficacy extending
several months after the last application of the
fungicide. The most effective triadimenol treat-
ments were two to three times costlier than the
standard aerial spray scheme used in the plantation
due to the high cost of the fungicide at the time of
the experiment.



can be absorbed by the roots and trdnslocated
to the leaves can be applied. A granular formu-
lation of triadimefon (Bayleton IGR, Bayer)
applied on the soil near the base of the pseu-
dostem has been reported by Mourichon (1982)
to have provided effective protection of banana
from sigatoka leaf spot caused by M. musicola
in the Ivory Coast. In this experiment triadi-
menol (Bayfidan 250 EC, Bayer), a new syste-
mic fungicide, was evaluated for efficacy against
the BLS and sigatoka diseases in Giant Caven-
dish banana by drenching it unto the base of the
pseudostem.

MATERIALS AND METHODS

The experimental area consisted of thirty
separate plots. Each plot was approximately
66 m2 containing 20 Giant Cavendish banana
mats spaced at 2.35 x 2.85 meters. Only 10
mats at the center of the plots were used as
indicator plants and each mat was made-up of 1
mother plant and 1 follower. The nine triadi-
menol treatments and the untreated control
were randomly assigned to the plots and were
replicated three times.
Triadimenol was evaluated at 1.0 g, 0.75 g
and 0.5 g active ingredient per mat, mixed in
310 ml water. Each of the three rates were'ap-
plied only six times at three different frequen-
cies of application i.e. once every 2 months,
once every 3 months and once every 4 months.
rhe triadimenol emulsion was applied by pour-






Jan. & June 1988 Evaluation of Drenching Triadimenol For Efficacy


ing it unto the base of the pseudostem of the
mother plant. Table 1 shows the schedule of
triadimenol applications from April, 1984 to
December, 1985.
Efficacy of the different treatments in con-
trolling the BLS and sigatoka diseases was based
on three parameters, namely; the disease incu-
bation period or the number of days it takes for
visible streaks to appear on the youngest ba-
nana leaf; the transition period or the length
of time for the streaks to turn into first-stage


spots; and the number of functional leaves on
the plant. The leaves of non-bearing bananas
were counted and examined once a week for
BLS and sigatoka streak and spot symptoms
starting from the first open leaf as leaf number
1 down to the succeeding older leaves. The
number of the youngest leaf on which the
streaks and the spots appeared was recorded
and the data were transformed into incubation
and transition periods using the following
formula:


Table 1. Scheme of application of the different dosages of triadimenol and check plot treatments


Dosages Frequency of Dates of Application
g.a.i./mat application


every 2 months



every 2 months


every 2 months


every 3 months



every 3 months


every 3 months
every 4 months



every 4 months


every 4 months


Plantation-
aerial spray-
ing w/fungi-
cide cocktails


10-15 days
interval


(4/10/84) (6/11/84) (8/10/84) (10/10/84)
(12/10/84) (2/11/85)


same as above


same as above


(4/10/84) (7/10/84) (10/10/84) (1/10/85)
(4/10/85) (7/10/85)

same as above


same as above
(4/10/84) (8/10/84) (12/10/84) (4/10/85)
(8/10/85) (12/10/85)


same as above


same as above


32 cycles in one year (April, 1984 to
March, 1985)
25 cycles from April to December, 1985.


0.75


0.5


0.75


0.75


Untreated
control


Jan. & June 1988


Evaluation of Drenching Triadimenol For Efficacy






Phlppn Phtvthlg Vo 24I


1. Incubation period (days) = number of the
youngest leaf with visible streaks multi-
plied by 7, since on the average, the Giant
Cavendish banana produces 1 opened
leaf every 7 days.
2. Transition period (days) = number of the
youngest leaf with first-stage spots minus
the number of youngest leaf with streaks
multiplied by 7. The transition period
was then rated poor = 14-20 days; fair =
21-27 days; good = 28-34 days; very good
= 35-41 days; and excellent = 42 days and
above.
Due to circumstances beyond control, only
40 data readifigs were accomplished from April,
1984 to March, 1985. The one-year data were
summarized and analyzed statistically. Treat-
ment means were compared using Duncan's
multiple range test (DMRT).


RESULTS AND DISCUSSION

Before the application of the various triadi-
menol treatments, there were no significant dif-
ferences in the incubation and transition
periods of the BLS and sigatoka diseases as well
as in the number of functional leaves of banana
in the different plots. When application of the
treatments began in April, 1984, the mean di-
sease incubation periods of the different treat-
ments from April to July, 1984 were shorter
than the pre-application incubation period of
16.43 days. However, in August, 1984, it in-
creased to 20.56 days and thereafter ranged
from 21.15 to 24.01 days. The mean transition
period for the streaks to turn into spots steadily
increased from 22.63 days before application of
the treatments to 28.15 days by July, 1984.
Then it ranged from 26.51 to 32.03 days'from
August, 1984 to September, 1985 before gra-
dually decreasing during the last three months
of the experiment. The average number of
leaves retained per plant also gradually increas-
ed from 7.24 leaves/plant before the applica-
tion of the treatments to 9.29 leaves/plant,
three months later in July, 1984. Thereafter,
it ranged from 8.5 to 10.1 leaves/plant.
The unfurling heart leaf and the first fully
open leaf are the major infection courts for
conidia and ascospores ofM. fiiensis and M.
musicola (Stover and Fulton, 1966). After a
few weeks, early disease symptoms consisting
of brownish-black streaks are initially exhibited
on the second, third or fourth leaf. The older


the leaf on which the streaks appear, the longer
will be the incubation period of the disease.
Streaks on the leaves develop into first stage
spots after several weeks. The older the leaf on
which the spots appear or the longer the transi-
tion period for streaks to turn into first-stage
spots is an indication of the relative efficacy of
a treatment since the length of time for spots to
appear and the number of spotting are known
to be correlated (Stover and Dickson, 1970).
Leaf spotting increases the rate of leaf
senescence and the life of a leaf can be
shortened by as much as 25% (Stover, 1974).
This effect makes the number of healthy or
functional leaves retained on the plant a useful
gauge for the disease control efficacy of a parti-
cular treatment.

Comparative Efficacy of the Treatments

All the triadimenol treatments provided
significantly longer disease incubation and
transition periods, and more functional leaves
than the untreated control.
During the one year period from April,
1984 to March, 1985, bananas drenched with
1.0 g triadimenol/mat once every three
months had the longest average disease incu-
bation period of 20.63 days (Table 2). This
was significantly better than the incubation
period of bananas applied with triadimenol at
1.0 g and 0.75 g once every four months and
0.5 g once every two months but it was not
significantly longer than those drenched with
the other rates and frequencies of triadimenol.
There were no significant differences inthe
transition periods for streak to become spots
in most of the triadimenol treated bananas.
Only those treated with 0.5 g/mat once every
four months had a significantly shorter transi-
tion period of 25.39 days (Table 3). The tran-
sition periods in all of the treatments indicated
fair control of the leaf diseases. Bananas
drenched with tridimenol at 1 g/mat once
every two months and once every three months
had a one-year average of 9.16 and 9.13 func-
tional leaves/plant, respectively. Their number
of leaves were significantly higher than those
treated with 0.75 g and 0.5 g triadimenol once
every four months but they were not signifi-
cantly different when compared with the
other rates and frequencies of triadimenol
(Table 4).
The different triadimenol treatments pro-


Vol. 24


Philippine Phytopathology






ulav ation of Drenchin
g T y


Table 2. Average incubation period (days) of the Sigatoka and Black Leaf-Streak diseases in the
different treated plants


AVERAGE INCUBATION PERIOD (DAYS)2/


Fungicide Rate Interval 1/ Post 1985
(g.ai/ ofappli- Pre application June Aug. Oct. Dec.
mat) cation appli- (Apr., 1984-
(months) cation (Mar., 1985)


Triadimenol 1.0 2 14.93a 20.32ab 24.55a 25.85a 24.03bc 21.23cd
Triadimenol 1.0 3 16.33a 20.6:a 24.55a 25.57a 27.18a 22.98a
Triadimenol 1.0 4 16.33a 19.76b 23.80ab 24.08abc 24.85ab 22.40ab
Triadimenol 0.75 2 16.80a 20.16 ab 24.27a 23.05bc 22.98bc 21.00d
Triadimenol 0.75 3 15.87a 20.04 ab 23.15ab 25.1lab 24.73b 21.93 be
Triadimenol 0.75 4 1633a 19.81b 22.96ab 23.15bc 23.80bc 21.82b
Triadimenol 0.5 2 14.47a 19.90b 23.52ab 22.77bc 21.58c 21.00d
Triadimenol 0.5 3 18.67a 20.16ab 2296ab 23.15bc 22.98bc 21.23cd
Triadimenol 0.5 4 17.27a 19.97ab 21.75b 22.49c 22.52bc 21.00d
Untreated control 17.27a 18.48c 17.92c 19.79d 17.85d 16.92e
MEAN 16.43 19.92 22.94 23.50 23.25 21.15



1/All treatments applied every 2, 3, and 4 months were started on April 4, 1984 and respectively terminated on
February 11, July 10, and December 10, 1985

2/ Means followed by the same letter are not significantly different at 5% level according to Duncan's multiple
range test.


vided only fair control of the BLS and siga- Residual Efficacy of Triadimenol
toka diseases during the one-year period from


tion periods were comparatively longer and
the number of leaves retained on the plants
were higher in the different treatments com-
pared with the control (Tables 2, 3 and 4).
Good control of the leaf diseases was par-
ticularly obtained in bananas treated with
1.0 g and 0.75 g triadimenol once every 2 and
Smnonths However higher dliease nrntrol


IUlOIlul anIu Iour monins were termmany
applied in February, July and December,
1985, respectively (Table 1). However, effi-
cacy of some triadimenol treatments against
the BLS and sigatoka diseases persisted
several months after the last application.
Triadimenol applied at 1.0 g/mat once
every three months provided significantly


Jan. & June 1981






Philippine Phytopathology


Table 3. Average transition period (days) of Sigatoka and Black Leaf Streak development


AVERAGE TRANSITION PERIOD(DAYS)2/


Fungicide Rate
(g.ai/
Mat)


Aug Oct Dec


Triadimenol 1.0 2 21.47a 27.88a 30.52a 30.52a 28.00ab
Triadimenol 1.0 3 22.40a 27.32ab 30.43a 29.49ab 30.22a


Triadimenol 1.0
Triadimenol 0.75
Triadimenol 0.75
Triadimenol 0.75
Triadimenol 0.5
Triadimenol 0.5
Triadimenol 0.5
Untreated control
MEAN


4 22.40a 26.62ab 29.96a 27.53ab 28.82ab 28,82a


2 22.40a 27.11ab 32.11a 27.53ab 27.42ab
3 21.93a 27.25ab 27.91a 30.15ab 28.12ab


25.55c
24.50c


4 21.93a 26.20ab 29.49a 27.07b 27.53ab 26.37bc
2 21.93a 26.79ab 29.87a 26.88b 25.90b 21.12d
3 26.13a 26.88ab 30.43a 27.16ab 25.67b 25.20c
4 22.40a 25.39b 28.56a 26.88b 26.72b 26.13bc


2333a 23.05c 16.80b
22.63 26.45 28.61


17.73c
27.09'


14.99c
26.34


14.35e
24.51


1 AIL treatments applied every 2, 3 and 4 months were started on April 4, 1984 and respectively terminated on
February 11, July 10 and December 10, 1985.

Means followed by the same letter are not significantly different at 5% level according to Duncan's multiple
range test.


of its last application in July, 1985 (Tables
3 and 4). Comparably long transition periods,
and more number of leaves were obtained
from the application oftriadimenol at 1 g/mat
once every two months until November, 1985
thereby indicating that its residual efficacy
lasts up to nine months since its final applica-
tion was in February 1985. Triadimenol at
0.75 g/mat once every two months and once
every three months remained effective for
eight and five months, respectively. Residual
action of triadimenol applied at the other
rates and frequencies was not clearly mani-
fested.


Cost Analysis and Recommendation

The fungicide applications used in the
standard spray scheme of Hijo Plantation Inc.
during 1985 cost P8,133.46/ha/yr. and the
aerial application fee amounted to P1,232.00
for the 32 cycles/yr. (Table 5), Among the
nine triadimenol treatments, only drenching
of 0.5 g/mat once every 4 months was less
expensive than the standard spray scheme
(Table 6). The most effective triadimenol
treatments, i.e. 1.0 g/mat and 0.75 g/mat
drenched once every 2 or 3 months, were two
to three times costlier than the standard spray


Interval 1/
of applica-
cation
(months)a


Pre-
appli-
cation


Post
application
(Apr., 1984-
Mar., 1985)


1985


June


24.62c
28.47ab


Vol. 24









fable 4. Effects of the different treatments on the number of functional leaves per plant.




AVERAGE NUMBER OF FUNCTIONAL LEAVES/



Interval 1/ Post 1985
Fungicide. (g.ai/ ofappli- Pre- Application
mat) cation appli- (Apr., 1984-
(months) cation Mar., 1985) June Aug. Oct. Dec.




rriadimenol 1.0 2 7.07a 9.16a 10.37ab 10.07a 9.97ab 9.00bc
rriadimenol 1.0 3 7.53a 9.13a 10.76a 9.47ab 10.95a 10.28a
rriadimenol 1.0 4 6.73a 8.72ab 9.95abc 8.87b 10.40ab 10.37a
rriadimenol 0.75 2 7.53a 9.04ab 10.75a 8.97ab 9.98ab 9.30b
rriadimenol 0.75 3 7.73a 8.98ab 10.09ab 9.85ab 10.45ab 9.13bc
Tr..-_nk It /n '7C A 7n @ o "I'.,. n AOL^ M O- nno n -oo,1


1a. June 1988 Evaluation of Drenching Triadimenol For Eff








Table 5. Fungicide formulation cost of the 32-cycles/year standard aerial spray scheme at Hijo Plantation, Inc.


Price/ kg
Quantity/ha (December, 1985)
(P)


Cost/ha/
cycle
(P)


No. of Formulation
cycles cost/ha/yr
per year (P)


Aerial spraying Total cost of formulation
fee/ha/year and aerial spraying/yr
(P) (P)


I Dithane M45

Banana Oil

Triton X45

II Calixin

Banana Oil

Lutensol

III Dithane F

IV Daconl

V Dithane M-45

Topsin M

Banana Oil

Triton X45


2.0 K

6.0 L

0.12 L

0.75 L

5.0 L

0.05 L

5.0 L

1.75 K

2.0K

032 K

5.0 L

0.05 L


62.8083

14.20

71.48

201.46

14.20

68.0295

48.5840

145.83

62.8083

390.00

14.20

71.48

TOTAL


Formulation


219.40





225.50

24292

255.20







325.00


2,852.2





676.50

728.76

1,276.00







2,600.00

8,133.46


500.50





115.50

115.50

192.50







308.00

1.232.00


-

3,352.70





792.00

844.26

1,468.50







2,908.00

9,365.46


8

32





ua. ilIUO IJV -JU L- IJIII


, ^ INllmlmr nf


6 5,292 31,752
4 5,292 21,168
3 5,292 15,876
6 3,969 23,814


1.0 2 4
1.0 3 4
1.0 4 4
3.75 2 3
3.75 3 3







Uf


LITERATURE CITED



LEACH, R. 1946. Banana leaf spot (Mycosphaerella STOVER, R.H. and J.D. DICKSON. 1970. Leaf spot
musicola) on the Gros Michel variety in Jamaica. of bananas caused by Mycosphaerella musicola:
118 pp., Kingston, Jaimaca, Government Printer. methods of measuring spotting prevalence and
severity. Trop. Agric. (Trinidad) 47: 289-302.
MOURICHON, X. 1982. Efficacite du Bayleton IGR
sur 1 evolution de la cercosporiose du bananier STOVER, R.H. and R. H. FULTON. 1966. Leaf
on Cote d'Ivoire. Fruits d'outre er 37: 291-293. spot of bananas caused by Mycosphaerella musi-
cola: the relation of infection sites to leaf devel-
STOVER, R.H. 1974. Effect of measured levels of opment and spore type. Trop. Agric. (Trinidad)
* sigatoka disease of bananas on fruit quality and 43: 117-129.
leaf senescence.. Trop. Agric. (Trinidad) 51: 531-
542.










ETIOLOGY OF
IN TH

Teodora O. Dizon, T. T. Reyes,

This study was supported by Institute of
rity (Project No. IPB-NSTA-UPS B 6603 Ag).
Respectively, Science Research Specialist,
Department of Plant Pathology, Research Asso
Professor, Department of Agronomy, University
Philippines.

ABS'

A new stem rot disease of ramie was observed
and reported for the first time. The disease is
caused by a fungus, Corticium rolfsii Curzi.
Symptoms of the disease were water-soaking
and browning of the basal portion of the stem fol-
lowed by wilting and defoliation of the plant.
Severely infected, plant turned brown and ulti-
mately died. Profuse growth of the mycelia of the
fungus covered the infected stem.
The fungus produced abundant mycelia on va-
rious agar media except on pechay agar, glycerine



INTRODUCTION



Ramie (Boehmeria nivea (L) Gaudich.) is
one of the most important fiber crops grown in
the country specifically in Mindanao areas
where it has been grown as early as 1909. In
1986, the total land area planted to ramie in
the Philippines was 6,478 ha which produced
72,941 bales of ramie fiber. The total hectar-
age grown to ramie reached 10,000 ha in 1987
due to the increased demand of ramie fiber in
other countries (FiDA, 1987).
In 1986, a survey of diseases of ramie was
conducted in Tranca, Bay, Laguna and Davao
provinces. In Davao, the predominant disease
was root knot while in Tranca, Bay, Laguna
the diseases observed were Cercospora leaf spot
and stem rot (Dizon, 1986). The stem rot di-
sease resembled that of seedling rot caused by
Rhizoctonia solani Kuhn (Summers, 1960) and
white rot caused by Sclerotium rolfsii (Sawada,
1931). However, closer examination of the


TEM ROT OF RAMIE
PHILIPPINES

,. San Pedro and R.P. Cabangbang

nt Breeding-National Science Technology Auth -

stitute of Plant Breeding, Associate Professor,
te, Institute of.Plant Breeding, and Associate
the Philippines at Los Banos, College, Laguna,


ACT

agar, sweet potato agar, and water agar. Good my-
celial growth was noted at 25, 30 and 35 C, with
maximum growth at 30C. At 40 C, mycelial
growth was completely inhibited. Continuous light,
continuous darkness and alternate light and dark
enhanced mycelial growth of the fungus. Longer
exposures to ultraviolet light (16 hrs. and 24 hrs.)
suppressed growth. The fungus did not produce
any fruiting Structures on agar media but formed
basidiocarps on the surface of inoculated, ramie
stem tissues. The fungus can infect many other
crops.



disease revealed that the symptoms were quite
different from those of the above mentioned
diseases. The disease was severe during moist
and cool conditions.
This study was conducted to identify the
causal organism of the disease, to study the cul-
tural and morphological characteristic of the
fungus and to determine its host range.



MATERIALS AND METHODS

Isolation and Purification of the Fungus

Stems of ramie infected with the disease
were brought to the laboratory for isolation.
White, profusely growing mycelia on the sur-
face of infected stem were aseptically scraped
with flame sterilized wire needle and placed on
potato dextrose agar (PDA) plate. The seeded
plate was incubated at 30 C under continuous
light until growth of the fungus was observed.
The isolated fungus was purified by subsequent
transfers to PDA slants.






30 Philippine Phytopathology VoL 24


Pathogenicity Test placed at the center of the plate. Seeded plate
was incubated at 30 C under continuous light.
Mycelial growth of the fungus on PDA plate Six temperature levels, namely, 15, 20, 25,
was placed at the base of 2 week old stem of 30, 35, and 40 C, were used. After seeding with
susceptible ramie variety, Seikeiseishin, grown mycelial disc, each PDA plate was inverted and
in the greenhouse. The symptoms produced on exposed at specified temperature level.
inoculated plants were described and compared Four light conditions were tested. These
with those of naturally-infected plants. were: continuous light (CL), continuous dark-
ness (CD) and alternate light and dark, 16 hr
Morphological Characteristics light 8 hr dark (ALDI), 16 hr dark 8 hr
light (ALD2) The effect of ultraviolet light
The characteristics of the mycelial growth of (UV) at various time exposures, namely 3, 5,
the fungus on PDA plate were described. Mor- 8, 16, and 24 hrs, was also studied. After expo-
phology of the hyphae from agar plate was ob- sure to UV light, the plate was incubated at
served under the microscope. Since the fungus 30 C under continuous light for 3 days at light
did not produce any fruiting structure on agar intensity of 18 foot-candle.
plate or slant, inoculation on healthy, detached In all tests, the size (mm) of the colony and
stems of susceptible variety was done. Mycelia the characteristics of the mycelial growth were
of the fungus were placed aseptically on the in- recorded 3 days after seeding. Three to 4 repli-
jured distal portion of surface-sterilized stem. cates were used for each treatment. The data
Inoculated stems were placed in sterile glass were statistically analyzed and the treatment
bottle with moistened filter paper and incuba- means were compared using Duncan's Multi-
ted at 30 C under continuous light. pie Range Test (DMRT).
The characteristics of the mycelial growth of
the fungus on stems were likewise described. Host Range Test
The morphology of the basidia, basidiospores
and sterigmata were examined under the mi- Different crops species were used in the
croscope and described. Moreover, the size of study (Table 1). The seeds of each species were


Cultural Characteristics

Mycelia of the pure culture of the fungus
were transferred to PDA plate and incubated
under continuous light at 30 C for 4 days. A
1.5 mm dia. mycelial agar disc was placed at the
center of the agar plate and used in subsequent
studies.
The effects of the various agar media, tempe-
rature and light conditions on the growth of the
fungus were studied. Fourteen media, namely,
Mycophil agar, Czapek dox agar, potato dex-
trose agar, sweet potato agar, carrot agar, pe-
chay agar, oatmeal agar, onion agar, yeast ex-
tract agar, coconut water agar, glycerine agar,
malt agar, water agar and V-8 juice agar, were
used. All the media were sterilized in the auto-
clave at 121 C for 15 min. About 10 ml of the
melted medium (50C) were poured aseptically
into sterile plate. A mycelial agar disc was


The early symptoms of the disease was the
Production of water-soaked lesions on the stem






jology Of Stem Rot Of Ram 31


f Corticium rolfsii


Peanut Arachis hy
Mungbean Vigna radi
Cowpea V. unquici
Soybean Glycine m
Cotton Gossypiun
Tomato Lycopersi
Corn Zea mays
Sorghum Sorghum I
Cucumber Cucumis s
Squash Cucurbita
Hot pepper Capsicum
Sweet pepper C annuun


Papaya Caricapac
Pole sitao V. sesquip






close to the soil surface or point of inoculation.
As the lesion enlarged it encircled the stem and
spread upward. In the advanced stage of infec-
tion, the infected stem turned brown, and the
plant wilted and defoliated. The fibers of
severely infected portion of the stem disinte-
grated. Later on, the surface of the infected
stem became covered with white mycelial
growth of the fungus which started from the
soil surface and progressed upward (Fig. 1).
Infected plants remained standing even if the
stems were already dead. The symptoms of the
disease differed from that of seedling rot caused
by R. solani in that the brown lesion in seedling
rot occurred only at the basal portion of the
stem which caused bending and death of the
plant (Summers, 1960). The disease also dif-
fered from white rot caused by Sclerotium
rolfsii in that with white rot, the fungus first
attack the root system which caused wilting
and vellowin nf leaves and bending of infected


I Variety/Line



)gaea L UPL-Pn-4
i L. Wilzeck. NCM-53
'ta Walp. CPH-6
(L.) Merr. TK-5
rirsutum L Deltapine 16
i esculentum Mill. C-108
Super sweet
olor Moench. SG-5
vus L Panorama
axima L San Puso
psici L. HP -86-124
L. California
Wonder
,a L Cavite Special
Wal is (L.) Fruw. WIR 487


























Fig. 1. Stems of ramie infected with Cor-
ticium rolfsii. Note the profuse white mycelial
growth of the fungus on infected stems.


able 1. Crops u


iology Of Stem Rot Of Ramn


31






32 rniippine rnyxopaimoogy v Tu.


plant (Sawada, 1931). Cultural Characterisrics

The effect of various agar media on myceli;
growth of the fungus is shown in Table 2. Their
Morphological Characteristics were significant differences among the differer
agar media used. The widest fungal colony wi
observed on pechay agar (7.80 mm) while tlI
The fungus grew rapidly on PDA plate. The narrowest was on gylcerine agar (5.32 mm
mycelia were white, abundant, appressed or Very abundant mycelial growth was found on]
aerial. Four to 5 days after plating, the mycelia on yeast extract agar, and abundant on Myc,
covered the surface of the agar medium and in phil agar, oatmeal agar and V-8 juice agar. C
other media, growth was sparse to very spars
some cases, mycelial growth extended into the In al media usd, th wa s spse to vy spsf
cover of the plate. The fungus did not produce aerial or appressed mycelia.
any fruiting structure on agar plate or slant.
The fungus produced the widest color
The hyphae were septated, broad, multi- (8.60 mm) at 30 C and narrowest (1.58 mm)
nucleated, hyaline and with clamp connec- 15 C (Table 3). Mycelial growth was abundai
tion.Hyphal fusions or anastomoses were com- at 25, 30 and 35 C but sparse at 15 and 20 i
only observed. The fungus did not grow at 40 C. Differenc
among temperature levels were highly signi:
The fungus formed white mycelia covering cant.
the surface of inoculated stem segments. It
The different light conditions caused sigr
produced basidiocarps on the surface 4 to 5
ficant differences in mycelial growth of tl
days after inoculation. Basidiocarps were ini- f
fungus (Table 4). The widest colony diamet<
tially pure white turning yellow buff with age.
When examined under the microscope, the was noted in cultures exposed to continuol
When examined under the microscope, the
ng med hmenium shoin numerous light (6.47 cm) and to 16 hr dark and 8 hr lig]
fungus formed hymeniu showing numerous (6.13 cm) duration. Longer exposures to U
basidia, each basidium bearing 4 basidiospores (3 ) duratn L r res
light (16 hrs and 24 hrs).suppressed myceli
attached to sterigmata. The basidia were stout ght hr n hr dressed yeli
single-celled, smooth, hyaline and measured growth of the fungus tremendously whi
3.26 4.06 p x 10.64 13.09 with a mean shorter exposures (3, 5, 8 his) resulted in sligl
of 3.66 x 11.86 p.. The shape varied from inhibition of mycelial growth. In all light cone
ovate, obclavate to clavate. The basidiospores tions, the fungus formed white, aerial ar
abundant mycelia. It was also observed th
were hyaline, smooth and were ovate or reni- abundant mycelia. It was also observed th
r. Thye, sm wi r- there was distinct zonation of the culture aft
form. They were generally small, with measure-
ments ranging from 1.80 4.05 p x 2.92 exposures to u ght regardless of length
4.27 /, and a mean of 2.34 x 3.95 /p. Four exposure. Furthermore, it was observed th
4.2 a d a m of 23 x 3 /1 F u f the fungus did not sporulate at different lgl
sterigmata were generally formed at the tip of the fungus did not sporulate at different lig
each basidium which measured from 3.15 condition
4.50 p in length, with a mean of 3.98 p

Based on the growth characteristics of the Host Rage Test
mucelia on PDA, characteristics and measure-
ments of basidia, and sterigmata, the fungus is Of the 14 crops inoculated, 12 were infec
tentatively identified as Corticium rolfsii Curzi ed, viz. peanut, mungbean, cowpea, soybea
(Sclerotium rolfsii Sacc.). Measurements of cotton, tomato, cucumber, squash, hot peppe
basidia were within the range reported by sweet pepper, papaya and pole sitao. Corn ar
Curzi (1932) as cited by Aycock (1966). How- sorghum were not infected. Initial symptom i
ever, the measurements of basidiospores were water-soaking of inoculated stem was observe
smaller. The morphology of the spores are more 3 to 5 days after inoculation. This was follo\
or less the same with that described by Curzi ed by wilting and girdling of the affected ste:
(1932). tissues.






& June 1988 Etiology Of Stem Rot Of Ramie 33


)le 2. Effect of the different agar media on mycelial growth of Corticium rolfsii'


SSize of Colony2 Characteristic of
(mm) Mycelial Growth

'echay 7.80 a white, sparse, aerial
)atmeal 7.47 ab white, abundant, aerial


tato dextrose
lion
ycophil
.rrot
8 juice
:apek dox


'eet potato


ast extract


ite r


ycerine


1Data taken 3 days after
2Each figure is the mean
different at 5% level with



e 3. Effect of diff

perature
(C)


7.00 bc
6.85 bcd
6.85 bcd
6.60 cde
6.05 def
5.92 def


5.90 ef


5.47 f


5.35 f


5.32 f




Means folio




e levels or

F Colony2
mm)


8d
<-i I


a abudaI L, aerial
Abundant, aerial
Abundant, aerial
Abundant, aerial
Abundant, aerial
Abundant, aerial
Sparse, slightly
aerial
, very sparse
appressed
, very abundant,
aerial
, very sparse,
oppressed
, very sparse,
oppressed


ot significantly




cium rolfsii1

characteristic of
/celial Growth


ite, very sparse, aerial


8.60 a white, abundant, aerial
3.90 c white, abundant, aerial
1.50 d no growth







Philiomine PIMvtopatho


.+ H... --nA;+.-tnn- n." l


Treatment Size,






Continuous light 6.47


Colony2 Characteristic of
m) Mycelial Growth


I A


J..---r- --- u






& June 1988 Etiology Of Stem Rot Of Ramie 35



LITERATURE CITED


COCK, R. 1960. Stem and other diseases caused by SAWADA, K. 1931. List of fungi found in Formosa.
sclerotium rolfsii or The Status of Rolfs Fungus Gov't Res. Inst. Taihokom,Formosa, 103 p.
ifter 70 years. North Carolina Agr. Expt. Stn.
Tech. Bull. No. 174, 202. SUMMERS, T. E. 1960. Diseases of abaca, jute, sisal
and ramie. In McGraw-Hill Encyclopedia of Sci-
ON, TEODORA O. 1986. Ramie Pathology. An- ence and Technology. McGraw-Hill Book Co., Inc.,
aual Report, IPB-NSTA-UPS Project No. B 8603 New York.
Ag, 19 p.

er Industry and Develonment Authority. 1987.




























o exnlDote cnaracterisic varaion wnen Mn&a auu uln wiu m,atc uL n. W auf
i two culture media. Correlation of some three isolates tested, one sorghum is(
cultural and morphological characters to elected from Central Mindanao Univel
Spathogenicity was determined. Bukidnon showed highest toxicity ir
iceptible disease reaction was shown by sistently gave the highest percent infe


INTRODUCTION workers have reported that R. solani produced
in vitro phenylacetic acid and its hydroxylated
Rhizoctonia sheath blight poses potential derivatives. These metabolites posses phyto
threat to sorghum production especially in toxic activity which produce typical blight
areas with light rains of prolonged duration symptoms on seedlings of several crops (Aoki
(Dalmacio, 1980). Normally, the disease starts et al., 1963, Mandowa, et al., 1980; Frank
from the basal leaf sheaths as water-soaked 1976). Akai, et al. (1960) reported the correla
spots with light brown or straw-colored center tion of pathogenicity with some characters or
and reddish to brownish border. The lesions culture media.
enlarge, form a typical banded pattern and This study was conducted to evaluate the
spread upward reaching as high as the panicle. variation in physiological, cultural and morpho
The infection developing on the affected leaf logical characteristics and virulence ofR. solanl
sheath causes wilting of the leaf (Dalmacio, et isolates infecting sorghum plants. An under
al., 1981). The causal fungus, Rhizoctonia standing of the pathogenic variability of R.
solani Kuhn, is soil-borne and survives between solant is essential in developing sorghum varie
cropping season as mycelium on crops like ties with broad spectrum and more stable resist
corn, rice, mungbean, other plants and weeds, ance to Rhizoctonia sheath blight.
and as sclerotial bodies in the soil. It has a
competitiveO saprophytic ability with high
pathogenic potential and wide host range. It is MATERIALS AND METHODS
also widely distributed, highly variable, and has
a wide range of temperature requirements Cultural and Morphological Variation
(Kernkamp, et al., 1952).
One of the contributing factors to the patho- R. solani, isolated from infected parts of
genic potential of R. solani is its ability to pro- sorghum, corn and mungbean were grown on
duce toxic metabolites. Besides tissue macera- two culture media, Potato Dextrose Agar (PDA)


duced by this path


---- ------~ IC----






Jan. & June 1988 Vajialion In Rhizoctonia Solani Kuhn


M, from mungbean were evaluated for their
colony diameter, growth rate, onset of sclero-
tial primordia formation, average size and num-
ber of mature sclerotia and distribution of scle-
rotial bodies. The data were analyzed as com-
pletely Randomized Design CRD with 3 replica-
tions.
Pathogenic Variation

The six isolates of R. solani from sorghum,
corn and mungbean were inoculated on one-
month-old sorghum plants variety UPL Sgo5,
using the leaf sheath-inoculation method
(Pascual and Raymundo, 1988). Incubation
period. % infection at two stages of growth and
disease reaction were determined. Correlation
analysis was used to determine the association
of some cultural and morphological characters
with virulence of the isolates.

Variation in Toxic Metabolite Production and
Percent Infection
The differences in toxic metabolites pro-
duced by R. solani were determined using
sorghum isolates, S1 from UPLB Experiment
Station and S2 from CMU, Musuan, Bukidnon
and corn isolate CI, from Banga, South Cota-
bato. All isolates were cultured in potato dex-
trose broth and incubated for 14 days at room
temperature. The resulting culture broth was
passed through filter paper and half of the
filtrate was autoclaved for 15 minutes at 15 psi.
The presence of toxin was determined thru root
length inhibition bioassay (Pringle and Scheffer,
1964) using the autoclaved and unautoclaved
filtrates.
UPL Sg-5, a susceptible sorghum variety, was
tsed to test the degree of infection caused by
R. solani isolates. One month-old test plants
were artificially inoculated with the three
isolates S1, S2 and CIl 1 using the leaf sheath
inoculation method. Virulence of the isolates
was determined -by measuring the percent in-
fection in each treatment one month after
inoculation in the screenhouse.

RESULTS AND DISCUSSION

Cultural and Morphological Variation
The six isolates differed significantly in
growth rate, onset of sclerotial primordia form-
ation, average size and number of mature
sclerotia, and site of sclerotial production
(Figures 1 & 2 and Table 1). Most of the iso-
lates produced sclerotial primordia on the third


and fourth day on PDA and cut sugarcane
leaves. Sclerotial production by most of the
isolates was of the scattered or dispersed type
which is similar to the findings of Fajardo
(1984) on R. solani isolates from rice. The
number of mature sclerotia produced by the
isolates per plate on PDA ranged from 11.6
to 161.0 while the size of sclerotial bodies
ranged from 1.6 mm to 4.0 mm. Sclerotia pro-
duced by the different isolates were brownish
in color and irregularly shaped but mostly
spherical with flattened bottom.
Isolate CI2 produced the highest number
but smallest size of mature sclerotial bodies, the
earliest to form sclerotial primordia and the
only one with aggregate type of sclerotial pro-
duction. On the other hand, S1 isolate from
sorghum exhibited the biggest colony size and
the fastest mycelial growth rate while the
mungbean isolate showed the slowest growth
rate.
Only a slight difference in size of sclerotial
bodies (0.3 mm) and number of days to sclero-
tial primordia formation (0.66 day) was observ-
ed on the two culture media used. This suggests
that sugarcane leaf is a good substrate for
inoculum production.
According to Kernkamp (1952), cultural
and morphological characteristics of R. solani
isolates are highly influenced by environment
such that only a slight environmental deviation
will produce variants.


-* / M1





LEGEND:


S20 / // / 0-o s SORGHUM ISOLATE
0A '----, CII2 CORN ISOLATE 12
: 15 /
- CIj CORN ISOLATE 11
10 --- CI4 CORN ISOLATE I1
5 ^-- C2 CORN ISOLATE 2
SMI MUNGBEAN ISOLATE
6 12 24 48
Hours After Inoculation
Fig. 1. Colony size and growth of R. solani
isolates at different periods after inoculation.


Jan. & June 1988


Variation In Rhizoctonia Solani Kuhn

















Rs -14 Corn RS .IZ Corn Rs.-l Corn


Philippine Phytopathology


vl0. Z4


B I


m


m


R R S;Serhul RS.Mur
Fig. 2. Morphological character
corn, sorghum and mungbean on PI




Table I. Cultural and morphological variation in

Days to sclerotial No. of mature
primordial sclerotia on
formation plated PDA

Isolate' PDA Sugarcane
Leaves



S, 4 3 77.6c

CIl 2.5 2.5 161.0a


uneter size Distribution of
m) of mature sclerotial bodies
erotia on plated PDA
'A Sugarcane Type of Site of
Leaves sclerotial sclerotial
production production

33ab 3.56a dispersed edge and
side






ian.&Junel988 Variation In Rhizoctonia Solon! Kuirn


Pathogenic Variation


Sorghum variety UPL Sg-5 exhibited a sus-
ceptible reaction to isolates Si, Cl2, Cli and
CIl4with percent infection ranging from 69.6 -
78.7% (Table 2). It took only one day for UPL
Sg-5 to develop lesions when noculated with the
sorghum and corn isolates. The mungbean
isolate caused lowest percent infection and the
longest incubation period. The response of UPL
Sg-5 to inoculation with different isolates of
R. solani from different crops revealed that this
fungus showed a level of specificity which is
restricted to a certain host range.

The correlation coefficients of some of the
cultural and morphological characters of the
isolates and their virulence are shown in Table
3. The degree of pathogenicity of the isolates
was not correlated with the number of sclerotia
and colony size. However, the weakly virulent
isolate (Ml) consistently gave the smallest
colony size and lesser number of sclerotial
bodies formed while the highly virulent sor-
ghum and corn isolates produced bigger colo-


nies and higher number of sclerotia. Size and
number of sclerotia are highly negatively cor-
related. These findings are in agreement with
previous studies on Pillicularia where pathoge-
nicity was found related to some morphologi-
cal characters of the isolates (Akai, et al.,
1960). Iacobellis (1987), also found that the
fast-growing Rhizoctonia isolates from beans
were more virulent than the slow-growing ones.
Similar results were also observed by Fajardo
(1984) on rice isolates ofR. solani.

Variation in Toxic Metabolite Production and
Percent Infection
The presence of toxin resulted in drastic re-
duction in growth of roots and the develop-
mett of the characteristic disease symptom
caused by R. solani (Table 4 and Fig. 3). Re-
sults showed further that isolate S2 produced
more toxic material that isolate S1 and CI11
although the difference between S, and Sz are
not significant. However, the difference in viru-
lence between S1 and S2 in terms of percent
infection was significant (Table 5). 'These dif-
ferences in toxicity of the toxin produced and


Table 2. Pathogenic variation of six Rhizoctonia solani isolates under screenhouse
condition using UPL Sg-5 sorghum variety

Isolates Incubation Ave. Lesion % Infection Host
Period length (cm) 30 DAI Reaction 2
(DAI)' 4 DAI

S1 1 8.2a 69.6a 5
CI2 1 8.6a 73.8a 5
CI11 1 8.2a 78.7 5
CII2 1 6.6b 44.3b 4
CI14 1 5.2c 71.6a 5
M1 3 3.0d 8.3c 2


1 DAI = Days After Inoculation

2 1 = Highly resistant
2 = Resistant


3 = Moderately Resistant
4 = moderately Susceptible
5 = Highly Susceptible


Note: Means followed by a common letter are not significantly different at 5% level.


Jan. & June 1988


Vaziation In Rhizoctonial Soldni Kuhn










Table 3. Correlation coefficients of some cultural and morphological characters of Rhizoctonia
solani isolates and their virulence




Computed r-value


Colony No. of mature Size of
size sclerotia sclerotia


Degree of pathogenicity


0.76


0.60


0.08


No. of mature sclerotia



Note: tabular r-value at 5% = 0.811, at 1% = 0.917
** highly significant



pathogenicity of the isolates on the test cultivar
UPL Sg-5 indicate physiologic specialization in
R. soiani isolates that were evaluated.
Many reports showed that blighting or wilt-
ing acitvity of R. solani is due to macerating
action of the enzymes it produces (Bateman,
1967). In this study, autoclaving did not affect
toxicity of the filtrate suggesting that toxic
activity is not only due to enzymatic action of
the fungus but also due to a non-proteinaceous
metabolite. The result agrees with the findings
of Kohmoto and Nishimura (1974). Since the
toxin is heat stable, it may also be used for in


-0.94**


vitro research of sorghum resistance to Rhizoc-
tonia sheath blight.
Toxic activity is not only due to the capabi-
lity of fungal isolate to produce toxin but also
on culture medium composition (Kernkamp,
1952). Furthermore, according to Kerkamp
(1952), Strobel (1974) and Wood (1972), the
toxin produced by the fungus generally
damages cell permeability resulting to inhibi-
tion of nutrient uptake and loss of electrolytes
of the host cells. As a consequence, the cells die
causing blight and wilts in the affected area.


Philippine Phytopathology


Vol. 24






Rhizoctonia Solani Kuhn


e 4. Root length of UPL Sg-5 at different concentrations of culture filtrate of three isolates of
Rhizoctonia solani and its corresponding toxicity index 48 hours after incubation.


ites1 Filtrate Mean Toxicity
concentration (%) Root Index3
Length (mm)2


0 47.3** 230.9ab
10 21.3*
50 7.2ns
100 4.0ns
100 (autoclaved) 3.8

0 53.6** 255.0a


100
100 (autocla

11 0
10
50
100
100 (autocla


= R. solani isolate from sorghum collected at Experimc
= R.solani isolates from sorghum collected at CMU, Bu
I = R. solani isolate from corn
ans followed by a common letter are not significantly
mmation of percent reduction in root length at different
= not significant, = significant,
** = highly significant (LSD).


2.5ns
d) 3.0

48.0** 211.3b
19.6*
14.0*
8.6ns
d) 9.1


Station, UPLB
Inon

ferent at 5% level. Toxicity index is the
ncentrations of culture filtrate.









.P .^


[1






42 Philippine Phytopathology Vol.



Table 5. Percent infection of UPL Sg-5 one month after inoculation with three of R. solani isolates



Isolate Mean percent infection 1


S1 68.3b
S2 93.0a
CI 1 65.0b


IMeans followed by a common letter are not significantly different at 5% level


LI 1



AKAI, S., H. OGURA and T. SATO., 1960. Studies
Pellicularia filamentosa (Pat.) Rogers 1. On re
tion between the pathogenicity and some chara
ers on culture media. Ann. Phytopathol. S
Japan 25:125-130.

AOKI, H., SASSA, T. and TAMURA, T. 1963. Phy
toxic metabolites of Rhizoctonia solani. Nati
(London) 200: 575.

BATEMAN, D.F. 1967. Alteration of cell wall co
ponents during pathogenesis by Rhizoctonia solar
In The Dynamic Role of Molecular Constituent
Plant Parasite Interaction. C.J. and I. Bruce-i
blishing Co., St. Paul. p. 58-79.

DALMACIO, S.C. 1980. Sorghum diseases in the PI
ippines. In Proc. International Workshop on S
ghum Diseases. ICRISAT, 1978,439 p.

DALMACIO, S.C., M. P. DAYAN and C.B. PASCU.
1981. Identification of sources of resistance
some major diseases of sorghum in the Philippin
Philipp. Phytopathol. 17: 38-46.

FAJARDO, J. 1984. Cultural and physiological vai
tion in Rhizoctonia solani Kuhn, causal organi
of rice sheath blight disease in the Philippines.
thesis, University of the Philippines at Los Ban

FRANK, S.A. and S.K. FRANCIS. 1976. The effect
Rhizoctonia solani phytotoxins on potatoes. C:
J. Bot. 54: 2536-2540.


ATURE CITED



IACOBELLIS, N.S. and J.E. DEVAY. 1987. Rhiz
S tonia solani pathogenesis in beans. Physiol. a
S Mol. P1.Pathol. 30: 421431.

KERNKAMP, M.F.D., S.M. CHEN and B.C. ORTEG
1952. Investigation on physiologic specializati
and parasitism of Rhizoctonia solani. Minnesa
Agr. Expt. Sta. Tech. Bull 200:36 p.
KOHMOTO,, K. and S. NISHIMURA. 1974. Patl
chemical studies on Rhizoctonia diseases. Ar
Phytopathol. Soc. Japan. 40: 79-85.

MANDAVA, N.B., R.G. ORELLANA, J.D. WA
THEN and J.F. WORLEY 1980. Phytotoxins in
solani: isolation and biological activity of
hydroxy and m-methoxyphenylacetic acids.
Agric. Food Chem. 28: 71-75.

PASCUAL, C.B. and A. D. RAYMUNDO. 1988.Inc
lation techniques used in sorghum diseases. Phil-
ippine Plant Breeding. 3(1): 9-10.

PRINGLE, R.B. and SCHEFFFER, R.P. 1964. Hi
specific plant toxins. Ann. Rev. Phytopathol.
133-156.
STROBEL, G. A. 1974. Phytotoxins produced
plant parasites. Ann. Rev.P1. Physiol. 25: 541-5(

WOOD, R.K.S. 1972. Phytotoxins in Plant Diseas
Acad. Pres. London.
YODER, 0. C. 1980. Toxins in pathogenesis. Aj
Rev. of Phytopathol. 18: 103-129.









IDENTIFICATION OF
SCREENING F(


Lolita M. Dolores a

Respectively, Research Assistant, Institute of I
aos Bafios, and Professor, Department of Plant Pal
hilippines at Los Banos, College, Laguna, Philippir
The authors wish to thank Miss Araceli L Alcac
manuscript.

ABSTR

Three distinct plant viruses were isolated from
squash fields at the CES, UPLB and in Putho
area in 1985. They were distinguished from one
another by mechanical or insect transmission, ex-
perimental host range and particle morphology.
Two of the viruses were mechanically transmissible
(SqMV, WMV). The third and the most destructive,
Squash Leaf Curl Virus (SLCV), is exclusively
whitefly transmissible. This virus was transmitted
to squash only which responded with severe leaf
curl, stunting, leaf nations and little leaf. Both
SqMV and WMV induced necrotic local lesions on
Chenopodium amaranticolor and C. quinoa while
Citrullus vulgaris responded positively with severe
mosaic and stunting to WMV isolate only. The




INTRODUCTION

Squash (Cucurbita spp.) is a popular vegeta-
le crop in the Philippines. It is grown mainly
s food on account of its nutritive value. As a
ash crop, it generates a sizeable income for the
farmers. However, squash production is limited
ly a number of factors and among these are the
diseases caused by viruses. They have been ob-
erved to be very severe during the last few
'ears and are believed to be responsible for the
educed quantity and quality of yield.
The current control measures include cultu-
al practices such as altering the planting dates,
veed control and chemical protection against
nsect vectors. These methods offer some hope
if suppressing plant viruses and their vectors
nd will supplement other control practices.
however, these are only partially effective and
ieed to be repeated yearly which add to the
:ost of production. The use of resistant varie-


)UASH VIRUSES AND
RESISTANCE


R. B. Valdez

nt Breeding, University of the Philippines at'
)logy, College of Agriculture, University of the

ipas for technical assistance and for typing this



,T

her plant species belonging to Aizoceae and
alanaceae were immune to all the three viruses.
electron microscopic examinations of infected
af samples in both leaf squash and leaf dip
reparations revealed long flexuous rod-shaped
rus particles of WMV and few spherical-shaped
rus particles of SqMV. Infected SLCV leaf
ip samples showed no virus particle under the
M requiring a specialr technique for prepara-
ons and examination.
Of the 72 squash accesions, lines and cultivars
;reened for resistance to WMV and SLCV, only
cc. 2Q6 showed moderate resistance to both viru-
!s. Six other lines were moderately resistant to
fMV but susceptible to SLCV.




ies is the least expensive control measure and
Lad been proven in the past as a reliable answer
o problems where pesticides and other control
measures fail. It must be emphasized though,
hat the integrated control approach will
provide more permanent solutions to most crop
protectionn problems (Nameth, et al., 1986).
An important factor that determines the suc-
ess in breeding for disease resistance is the
availabilityy of sources of resistance. While genes
hat confer resistance to viral infections have
)een shown to be generally stable, in some
:ases, resistance is strain-specific. Thus, a resist-
nce gene may confer resistance only to a speci-
ic strain of a given virus requiring an accumula-
ion of genes for the control of all known
>athotypes (Provvidenti, 1986).
More than 25 viruses including seven that
belong to the potyvirus group were reported to
)ccur naturally in cucurbits (Lovisolo, 1981;
'urcifull, et al., 1984). Of these, the best







44 t'Iulippine I'bytopatbology


known, most widespread and most important
are cucumber mosaic virus (CMV), squas
mosaic virus (SqMV), watermelon mosaic virus-
WMV-1), watermelon mosaic virus-2 (WMV-2
and tobacco ringspot virus (TRSV) (Salama an
Sill, 1968). The relatively new ones are squash
leaf curl virus (SLCV), lettuce infectious ye:
low virus (LIYV) and Zucchini yellow mosai
virus (ZYMV).
Provvidenti (1986) reviewed the resistance
of cucurbits to various viral diseases. Include,
in his report were important viruses of squash
together .with their corresponding sources o
resistance. CMV and SqMV are spherical
WMV-1, WMV-2 and ZYMV are flexuou
rods, while SLCV are geminate. Except fo
SqMV and SLCV, which are transmitted b,
beetles and whiteflies respectively, all the othe
viruses are aphid transmissible.

In the Philippines, very limited studies an
available on viruses affecting squash. In a surve,
of virus and virus-like diseases of cucurbits
Bonus (1981) found CMV to be the most natu
rally occurring virus in squash fields. The othe
reported viruses were WMV (Protacio and Pa
cumbaba, 1958; IBP Annual Report, 1979
Marges,- 1976) SqMV (Roxas, 1986). The oc
currency of squash leaf curl disease was re
ported by Benigno in 1979.

Although these squash viruses occur in th<
field, their identity and their relationships witl
the other common cucurbit viruses have no
been well studied. The occurrence of one or
mixture of these viruses poses serious problem:
to squash growers.
An outbreak of virus diseases was observed
on squash fields in March, 1985 at the UPLI
Central Experiment Station and other areas ii
the Southern Tagalog Region. Affected plant:
showed symptoms of severe mosaic, chlorosi:
and leaf distortion, mottling, vein banding, lea
curling, stunting and little leaf that resulted ir
reduced yield. There was also a high incident(
and vigorous activity of aphids, squash beetle:
and whiteflies in these places (Dolores, et al.
1988).

This study reports on the isolation and iden
tification of viruses infecting squash and screen
ing for sources of resistance to these viruses


MATERIALS AND METHODS

Isolation and virus detection. Isolatil
was made by mechanical and/or insect transit
sion to both the local lesion host, Chenop
dium amaranticolor, Coste et Reyn. and tl
original systemic host, Cucurbita moscha
Duch. cv. Batac. Each virus isolate was purified
and maintained by a series of transfers froi
C amaranticolor to squash using mechanic
and/or insect transmission tests. Grouping (
the virus isolates was made based on sympton
exhibited on C amaranticolor and squas]
Three virus isolates were obtained from ii
fected squash plants exhibiting symptoms <
severe mosaic, severe blistered mottle, market
chlorosis and leaf curl, veinbanding and lei
rugosity, leaf nations, leaf distortion, little le;
and stunting. The virus isolates were distill
guished from one another by mechanical ini
culations onto Chenopodium anaranticolor an
Cucurbita moschata cv. Batac. and/or by inse<
transmission tests.
Virus isolate numbers 1 & 2 were purified b
repeated alternate inoculations onto C. am
ranticolor and squash cv. Batac. The oth(
virus isolate (SqV-3), which was not sap-tran
missile, was maintained on squash by a serif
of transfer from infected to healthy squas
plants using whiteflies as vectors.
Transmission. In the sap-inoculation test:
each virus inoculum was prepared by macer,
ting infected leaves in 0.05 M phosphal
buffer, pH 7.5 in heat sterilized mortar an
pestle. A 1% celite was added as an abrasive an
then rubbed lightly using the finger tip on full
expanded and succulent leaves of the te!
plants. Inoculated plants were rinsed imm(
diately with tap water.
In the insect transmission tests, aphic
(Aphis gossypii Glover) and whiteflies (Bemisi
tabaci Genn) were used as insect vectors for th
different virus isolates.
Virus-free aphids were first allowed to fee
on plants infected with each virus for 10 m
nutes. Then, 10 viruliferous aphids were tran:
ferred to each test plant for an overnight inc
culation feeding period. Later, the plants wei
sprayed with Malathion insecticide to kill th
aphids.
Similarly, non-viruliferous whiteflies wer


44


Prnlippme rnytopatnology







nuncanon in ~quaan virus 45


ce: Isolation and virus detection
vim-r ieMlatN MTn 1 (/nV.l in


Both the SqV-1 and SqV-2
... the SnV-3. induced necrotic In


first and second The other plant species tested,
succeeding leaves alobosa. Datura metel L. Tet


45


nuncanon uI squasn virus






Vnl 74


P 1.1; D Jlk Ur tf5 I


Fig. 1. Clcurbita moschatu
leaf distortion and ,



















Fig. 2. Chenopodium amn
lesions induced by 1



















Fig. 3. Squash accession e:
and leaf distortion ,


lowing severe blistered mottle,
nting to SqMV isolate.



















nticolor with necrotic local
IV isolate.



















biting severe mosaic, rugosity
linst WMV isolate.


Ilhili~;nn D1r~rrln~1-l^^-










Table 1. Reactions of three Philippine squash virus isolates on selected indicator hosted.


VIRUS REACTION

INDICATOR HOST SqMV WMV SLCV


Chenopodiaceae:
Chenopodium amaranticolor


C. quinoa
Aizoceae:
Tetragonia expansa
Gomphrena globosa

Cucurbitaceae:
Cucumis melo


C sativus


Cucurbita moschata cv.
cv. Batac
C. moschata
cv. Sampuso
Citrullus vulgaris cv.
cv. Charleston Gray
Luffa acutangula

Solanaceae:
Nicotiana glutinosa
N. tabacum
Lycopersicon esculentum
Datura metel
D. stramonium


pinpoint
nil; ns
nll; ns


NR
NR


mo; mos;
chl sp
vc; mo
ys
sb mo;
Ic; st
sm; st


NR


NR


big nil;
ns
nil; ns


NR
NR


sm; chl; NR


vb; sld;
st
vb; sld
st
sm; sld
st
sm; vb


NR


NR


Ic; chl
11; Ic
Ic; chl


NR


NR


Legend:


- necrotic local lesions. not systemic
- vein clearing
- chlorotic spots
- chlorosis
- severe blistered mottle
- mottling
- mosaic
- yellow spots


- severe mosaic
- leaf nations
- vein banding
- severe leaf distortion
- leaf curl
- stunting
little leaf
- No reaction


nll; ns
vc
chl sp
chl
sb mo
mo
mos
ys


Jan. & June 1988


Identification Of Squash Viruses






Philippine Phytopathology


Thunb., and Lycopersicon esculentum Mill. DISCUSSION
were immune to the three virus isolates.
Summary of results obtained on the identi
In the insect transmission tests, only the cation of these three squash virus isolates a
SqV-2 isolate was transmitted by Aphis gossy- shown in Table 2. The spherical SqV-1 isola
pii in a non-persistent manner. Provvidenti resembled squash mosaic virus (SqMV) iden
(1986) reported CMV, WMV and ZYMV to be fled by Freigtag (1941). While CMV has sphe
transmitted by a number of aphid species inclu- cal virus particles and is transmitted by aphi
ding Aphis gossypi. SqV-3 was transmitted by in a non-persistent manner, our results in tl
B. tabaci after a 1-hr acquisition/24-hr inocula- study showed that Aphis gossypii failed
tion access feeding periods suggesting that transmit SqV-1. Furthermore, N. glutinoi
tion accession s fee persistent type. On the which was reported to be a diagnostic host f
transmission was of a persistent type. On the CMV, remained immune to this virus isolai
CMV, remained immune to this virus isolal
otherhand, SqV-1 was not transmitted by any The symptoms produced on squash and oth
of the insect vectors used. These insect vectors cucurbitaceous species consisting of seven
were observed to be the most prevalent in blistered mottle, mosaic, and stunting conform
squash fields and are believed to be largely res- ed with the reports of Freitag (1941) a
ponsible for the spread of these viruses in the Campbell (1971) for squash mosaic vin
field. The presence of squash beetles was also In the case of SqV-2, which was distinguish
highly noted, but the difficulty of handling this from the two other virus isolates by its lo
insect vector made it impossible for use in flexuous rod-shaped particles, was identify
transmission tests. as watermelon mosaic virus (WMV). T
distinct reaction caused by this isolate diff
entiated it further from the two other isolat
Morphological charactenistics.-- Leaf dip Watermelon was reported to be resistant
preparations of the three virus isolates from in- CMV and SqMV by Smith (1972). Campb
fected squash leaves showed few spherical virus (1971) mentioned watermelon to be the
particles of SqV-1. and long flexuous particles mary host of WMV but was generally immu
of SqV-2. No virus particle was seen on samples to CMV. On the otherhand, CMV produce
infectedd with the SqV-3 isolate which required marked symptoms on Nicotiana species.
a special method of purification and prepara- 1979, Talens obtained positive results usi
tion for election microscopy. N. glutihosa L. as systemic host for CMV t
,. ....- ..1 . .


lu. a S,1sCV I IoLU
and SLCV are to
A - 'lrtz4 '


only but susceptible to SLCV. Accessions
276, 11-294, 82038 and 5019 K 7 were moc
ately resistant to SLCV only. La Preciosa i
81017, which were found by Roxas (1984)
be moderately resistant to SqMV only w
susceptible to both WMV and SLCV. None
the 72 accessions tested was rated resistant
the two viruses. The rest of the accessic


the isolate were also similar to the leat c
virus disease described by Bonus (1981). 1
disease was distinguished from the leaf c
without nations having aphids as vectors i
flexible rod particles (Clark, et al, 1980)unl
the whitefly-bore leaf curl with enatii
having geminate virus particles (Yamachi, el
1976). On the other hand, symptoms such
^ ^^c .... i.:. -.- -; .-I ^ . i:r.. *^^ .rt.as


48










ie 2. Summary of results on the identification of three Philippine squash virus isolates.





TRANSMISSION


(SqMV) +






;(WMV) +







(SLCV)













iated with plants se
rus especially when it
lermore, plants fail t
fruits and some
no virus particles
on microscope using
.ip methods, techniqt
and EM preparation
i, et. al (1983) will


+




lesions

+







+






with symptoms
)- no symptoms





:d with logical s
d early. confirmE
illy, set The (
) death viruses c
der the the dynm
eaf and is consta
iurifica- product
hied by infection
id sero-


49


illertion OI Saush VIruer






50 Identification Of Squash Viruses Vol. 24


Table 3. Results of screening 72 squash lines/accessions, and cultivars for resistance to WMV a
SLCV


LUUSJNEEEChTL.
ACC/CULTIVAR SOURCE WMV SLCV



A-206 NPGRLa MR MR
11-214-1 x Veg. Breedingb MR MS
11-28 Veg. Breeding MR S
11-296 Veg. Breeding MR S
11-297 Veg. Breeding MR S


11-306 Veg. Breed
11-276 Veg. Breed
11-294 Veg. Breed
5019 #7 x East-West
La Preciosa East-West
81017 East-West
82038 East-West
A-202 NPGRL
A-215 NPGRL
11-2 Veg. Breed
114 Veg. Breed
81014 East-West!
*A-225 Veg. Breed
11-14-2-10 Veg. Breed
11-286 Veg. Breed
11-292 Veg. Breed
!-304 Veg. Breed
11-312 Veg. Breed
11-25-2-2 X BPI 7 Veg. Breed
A-110 NPGRL
A-205 Veg. Breed
11-25-1-6 x Veg. Breed
A-227 NPGRL
11-299 Veg. Breed
11-316 Veg. Breed
11-211-3x11-211-9 Veg. Breed
11-25-2-9 Veg. Breed
A-203 Veg. Breed
A-211 Veg. Breed
A-212 Veg. Breed
A-214 Veg. Breed
11-210 Veg. Breed
BPI Golden Veg. Breed


g MR S
g MS MR
7 MS MR
,d Co. S MR
-d Co. HS MS
ed Co. S HS
-d Co. S MR
MS MS
MS S
g MS S
7 MS S
ed Co. MS S
g MS HS
3 MS HS
g MS HS
g MS HS
SMS
g MS HS
SMS HS
MS HS
g S MS
g HS MS
HS MS
I S S
SS HS
g S HS
SS -
g S S
g S S
g HS S
g S S
g HS S
g HS S






Jan. & June i~va rnmppine rnytopainoiogy 31


cont of Table 3.

VIRUS INFECTION
ACC/CULTIVAR SOURCERUS INFECTION
WMV SLVC

Dolores Veg. Breeding HS S
11-277 Veg. Breeding S HS
11-314 Veg. Breeding S
82036 East-West Seed Co. S -
A- 9 NPGRL HS -
A-56 NPGRL HS
A-74 NPGRL HS -
A-75 NPGRL HS -
A-84 NPGRL HS -
A-86 NPGRL HS HS
A-88 NPGRL HS HS
A-90 NPGRL HS HS
A-102 NPGRL HS HS
A-108 NPGRL HS HS
A-112 NPGRL HS HS
A-122 NPGRL HS HS
A-199 NPGRL HS S
A-200 NPGRL HS HS
11-25-2-9 Veg. Breeding HS HS
11-26-14 Veg. Breeding HS HS
11-210 Veg. Breeding HS HS
11-211-10 Veg. Breeding HS HS
11-25-1-6 x Veg. Breeding HS HS
11-25-1-7 x Veg. Breeding HS HS
11-211-10 x Veg. Breeding HS HS
11-315 Veg. Breeding HS -
82039 East-West Seed Co. HS -
A-219 Veg. Breeding HS HS
11-272 Veg. Breeding HS HS
11-14-2-10 Veg. Breeding HS
Sampuso Veg. Breeding HS HS
Batac Veg. Breeding HS HS
82039 East-West Seed Co. S MR




aNational Plant Genetic Resource Laboratory Institute of Plant Breedng, UPLB, College, Laguna
bVegetable Breeding
Institute of Plant Breeding, UPLB, Philippines
CEast-West Seed; Co., Lipa, Batangas, Philippines
- not tested due to lack of seeds







Phlppn Phtpthlg Vol.2


LITERATURE CITED


BENIGNO, D.A. 1979' Note: Leaf curl disease of
Squash. Philipp. Agr. 61:304-305.

BONUS, M. 1981. A survey of virus and virus-like
diseases of cucurbits in the Philippines. M.S.
Thesis, UPLB, College, Laguna. 71 p.

CAMPBELL, R.N. 1971. Squash Mosaic Virus, In
Descriptions of Plant Viruses, No. 43. Common-
wealth Mycological Institute and Association of
Applied Biologists, Kew, Surrey, England.

CLARK, R.L., J. HILL and M.O. ELLIS. 1980.
Tomato scorch, a new virus disease of tomatoes.
Phytopathology 70: 131-134.

COHEN, S., J.E. DUFFUS, R.C. LARSEN, H.Y. LIU,
and R.A. FLOCK. 1983. Squash leaf curl virus:
Purification, serology and vector relationships of
the whitefly transmitted gemini virus. Phytopatho-
logy 73: 1669-1673.

DOLORES, L.M., R.B. VALDEZ and V. P. ROXAS.
1988. Viral diseases of Squash (Cucurbita spp.) in
the Philippines and sources of resistance. Paper
presented at the 4th FCSSP Annual Scientific
Conference held in Davao City on April 27-29,
1988.

FREITAG, G.H. 1941. Insect transmission, host range
and properties of squash mosaic virus. Phytopa-
thology 31:8. (Abstr.)

GREEN, S.K. 1984. Guidelines for diagnostic work in
plant virology. Techical Bulletin No. 15 AVRDC,
39 p.

INSTITUTE OF PLANT BREEDING 1979 Annual
Report. UP Los Bafios, Collage, Laguna.

LOVISOLO, O. 1981, Virus and viroid-diseases of
cucurbits, Acta Horticulture 88:33-71.

MARGES, C.E. 1976. Investigations on the mosaic
diseases of watermelon, muskmelon and cucumber.
B.S. Thesis, UPLB, College, Laguna. 44 p.


NAMETH, S. T., J. A. DODDS and A. O. PAULUS.
1986. Cucurbit viruses of California: An Ever
Changing Problem. Plant Disease 70 (1).

PROTACIO, D.B. and E.P. PACUMBABA. 1970.
Watermelon mosaic in Bicol Region (Abstr.)
Philipp. Phytopathol. 6:10.

PROVVIDENTI,, R., R.W. ROBINSON and H.M.
MUNGER. 1978. Resistance in several species of
six viruses infecting Cucurbita. Pit. Dis. Reptr.
62:326-329.

PROWIDENTI, R. 1986. Viral diseases of cucurbits
and sources of resistance. In Plant Virus Disease
of Horticultural Crops in the Tropics and Sub-
tropics. FFTC Book Series No. 33 pp. 221-36.

PURCIFULL, D.E., W.C. ADLERZ, G.C. SIMON, E.E.
HIEBERT and S.R. CHRISTIE. 1984. Serological
relationships and partial characterization of Zuc-
chini Yellow Mosaic Virus isolated squash in Flo-
rida. Pit. Dis. Reptr. 68:230-233.

ROXAS, V.P. 1986. Screening for resistance to squash
mosaic virus and selection for hosticultural traits
in squash (Cucurbita moschata Duch.). B.S. Thesis
University of the Philippines at Los Banos, College
Laguna.

SALAMA, E.A. and W.H. SILL. 1968. Distribution of
cucurbit viruses in Kansas. Pit. Dis. Reptr. 52:11-
14.

SMITH, K.M. 1972. A textbook of plant virus diseases.
Longman, London 670 p.

WEBB, R.E. 1965. Luffa acutangula for separation
and maintenance of watermelon mosaic virus-i
Tree of watermelon mosaic virus-2. Phytopatho-
logy 55:1379-1380.

YAMACHI, A., A. IMOTO, T. HIBI and Y. KUMURO,
1976. Trialeurodes vaproriorum (Westwood) tobac-
co leaf curl virus. Ann. Phytopathol. Soc. Japan
42:424-430.


Vol. 24


Philippine Phytopathlology




Philippine Phytopathological Society, Inc.
1988 Phil Phytopath. 24: 53 56


NOTE: SOURCES OF RESISTANCE TO STEM ROT IN RAMIE

Teodora O. Dizon, T. T. Reyes, J. L.
San Pedro and R. P. Cabangbang

This study was supported by Institute of Plant Breeding-National Science Technology Authority
(Project NO. IPB-NSTA-UPS B 6603 Ag).

Respectively, Science Research Specialist, Institute of Plant Breeding (IPB), Associate Professor,-,
Department of Plant Pathology, Research Associate, IPB and Associate Professor, Department of
Agronomy, UP at Los Bafios, College, Laguna, Philippines.


ABSTRACT


Of six methods evaluated, inoculation at the
base of the stem, inoculation of the injured stem,
50 mm and 100 mm above soil surface produced
symptoms of stem rot.

INTRODUCTION
Stem rot caused by Corticium rolfsii Curti
(Sclerotium rolfsii Sacc) is a new disease of
ramie in the Philippines (Dizon, 1986). The
disease can be a serious threat to ramie produc-
tion due to the soil-borne nature of the pathogen.
Normally, natural field inoculation is a good
method of evaluating disease resistance. How-
ever, due to several difficulties encountered in
the field, such as antagonistic or synergistic
effect of other pathogens and other factors
influencing disease development, a rapid but
reliable and effective method must be develop-
ed. This is a more logical approach especially
when one is evaluating large number of materials.
One of the main components of breeding for
disease resistance is the identification of resist-
ant sources as these constitute the materials
upon which programs must be based. Since soil-
borne pathogens are widely distributed and
have a wide host range, an intensive search for
resistant materials to stem rot in ramie must be
done. This study therefore was conducted to
develop an effective and reliable inoculation
method for use in screening and to identify
sources of resistance to stem rot.

-MATERIALS AND METHODS

Source of Inoculum

Pure culture of Corticium rolfsii was grown
in potato dextrose agar plate for 5 days. Two
sources of inoculum, namely, mycelial agar


Of 48 introduced and local lines and varieties of
ramie screened against the disease, one was found
resistant and two were moderately resistant.


growth fragments of the fungus and rice: rice
hull (1:3 v/v ratio) with mycelial growth of the
fungus (cultured substrate), were used.

Inoculation Methods Evaluated

Six inoculation methods were evaluated.
These were (1) rice: rice hull with mycelia
placed at the base of the plant, (2) mycelial
agar growth mixed with the potted soil and
planted to ramie seedlings, (3) mycelial agar
growth taped at injured stem, 50 mm above
soil surface, (4) mycelial agar growth taped at
injured stem, 100 mm above soil surface, (5)
mycelial agar growth taped at uninjured stem,
50 mm above soil surface, and (6) mycelial agar
growth taped at uninjured stem, 100 mm above
soil surface. Plain PDA agar taped on stem of
ramie seedlings served as control.
The characteristic symptoms that develop-
ed on the inoculated plant and the incubation
period were recorded.

Test Variety Used

A susceptible ramie variety, Seikeiseishin,
was used as test plant. Seeds were sown in seed-
boxes containing sterile soil covered with ash
and then enclosed with rice hull. When the
seedlings were at about 3 to 4 leaf stage, they
were transplanted individually into No. 7 clay
pots with sterile soil. One week after transplant-
ing the seedlings were inoculated using the
methods described above. Three pots with three






Philippine Phytopathology


seedlings each were used for each inoculation
method.

Evaluation of sources of resistance to stem rot

Forty-eight introduced and local ramie lines
and varieties were screened for stem rot resist-
ance in the greenhouse. Rhizomes were used
instead of seedlings from seeds. These were col-
lected from plants maintained in pots and
allowed to produce plantlets by incubating
them in moistened jute sack. Plantlets of about
50 mm length were transferred to seedboxes
containing sterile soil. Ten plantlets were used
for each line or variety.

Inoculation and Gathering of Data

The method employed was inoculation at
the base of the plant which was the most effec-
tive and reliable method found earlier. About
35 grams of the cultured substrate with mycelia
were inoculated into the base of one week old
ramie plantlets. The number of plants that
wilted were counted 20 days after inoculation.
The different lines and varieties were classified
using the following rating index:


Percent Wilted Plant


1 15
16 30
31 -45


Reaction


Highly resistant
Resistant
Moderately resistant
Moderately susceptible


46 -60
61 100


Susceptible
Highly susceptible


RESULTS

Development of Inoculation Method

Of the six methods evaluated, application of
the cultured substrate with fungal mycelia at
the base of the plant and inoculation of injured
stems, 50 mm and 100 mm above soil surface
showed positive results. Symptoms of the
disease, such as initial water-soaking and brown-
ing of inoculated portion of the stem followed
by wilting and defoliation, were observed 5 to6
days after inoculation. When the point of ino-
culation was 100 mm above soil surface, the
leaves above the point of inoculation wilted.
However, there was profuse lateral leaf growth
below the point of inoculation. Plants inocu-
lated at the base of the stem and at 50 mm
above soil surface did not recover. The other
inoculation methods failed to elicit symptoms
of the disease.

Sources of Resistance

Of the 48 introduced and local ramie lines
and varieties screened against stem rot, shira-
ginu was found resistant while American and
Koshin-shu 2 were moderately resistant. Other
lines and varieties were rated either susceptible
or highly susceptible (Table 1).


VoL 24










Table 1. Reaction of the different ramie lines and varieties to stem rot caused by Corticium rolfsii


Line/Variety % Wilted Planta Reactionsb

Shiraginu 10 R
American 20 MR
Koshin-shu 2 30 MR
Tatsutayama 50 S
Hilshoro 50 S
Kawaminami 3 60 S
Seikeiseishin-shu 3 60 S
Kumamoto Zairal 60 S
Hakuni 16 60 S
Muri kami 70 HS
Seedling Selection 70 HS
Miyazaki 112 70 HS
Hakuhi-shu 70 HS
Koshin-shu 70 HS
Kogai 80 HS
Yilan 80 HS
Kagi-sei 80 HS
Shirakawa 80 HS
Seikeiseishin-shu 5 80 HS
Yamagata Zairai 1 80 HS
Seikeiseishin 90 HS
Seikeiseishin-shu 6 90 HS
Seishu 90 HS
Yamagata Zairai 2 90 HS
Okinawashu 90 HS
Seishun-shu 3 90 HS
Ishikawa-Zairai 90 HS
Kagoshima-Zairal 2 90 HS
Aokaze (Kawaminami 2) 100 HS
Seikeiseishin-shu 4 100 HS
Seikeiseishin-shu 2 100 HS
Seishu 3 100 HS
Leyte 1 100 HS
Hakuhi 80 100 HS
Seishinshu 100 HS
Seishin 1 100 HS
Kagisanshu 1 100 HS
Benibanashu 1 100 HS
Benibanashu 3 100 HS
Hosobenibanashu 100 HS
Shirobanashu 2 100 HS
Shirobanashu 2 100 HS
Aomori-Zairai 100 HS
Fukushima-Zairai 1 100 HS
Fukushima-Zairai 2 100 HS
Yamagata Shirohashu 100 HS
Kimotsuki-Zairai 100 HS
Kimotsuki-Zairai 100 HS
Teraploid Hakuhi 1 100 HS

Number of plant that wilted X 100
a% Wilted Plant =
total number of plants inoculated
bRating index: 0% wilted plant, highly resistant (HR); 1-15% resistant (R); 16-30%, moderately resist-
ant (MR); 31-50%, moderately susceptible (MS); 51-60%, susceptible (S); 61-100% highly susceptible (HS).


Jan. & June 1988


Note: Sources Of Resistance To Stem Rot In Ramie






56 Philippine Phytopathology Vol. 2


LITERATURE CITED

0. 1986. Ramie Pathology Annual Report, IPB-NSTA-










THE TWENTY-FIFTH Ai%
PHILIPPINE PHYTOPA'
CEBU CITY, 1


Suppressiveness of High Nitrogen Against Scle-
rotium Wilt of Tobacco. P.N. Dipon and S.G.
Sugui. Philippine Tobacco Authority (PTA)

An inverse relationship between Sclerotium
wilt incidence and nitrogen in the soil was'
observed. The disease was significantly lower at
60 to 120 kg N/ha than at 30 kg N. Highest
degree of suppression of disease incidence was
attained at 120 kg of N/ha, where the infection
rate was r= 0.01 per unit per week. The infection
rate, at 30 kg N was 0.05 per unit per week.
Disease was most serious near the end ofprim-
ing which coincided with the period of hot
weather.
Although the disease progressed faster near
the end of priming, there was minimal effect
on yield since disease incidence was low during
the early part of the season. Good leaf yield
nd .quality were obtained at the early part of
the growing season wl.en tobacco plants were at
their mid-vegetative growth.
Increasing level of nitrogen increased yield
but reduced quality of cured leaf. Cured leaves
were dark brown in color and of poor quality at
ligh nitrogen. Good quality was attained at low
nitrogen level.

Identification of Major Seed Potato Storage
Diseases in Benguet and Mountain Province,
Philippines. J.S. Luis and A. J. Quimio. Benguet
State University (BSU) and University of the
?hilippine at Los Banos (UPLB)

A four year survey (1983-1986) was under-
:aken to identify major seed potato storage
)athogens in Benguet and Mountain Province.
Fusarium sambunicum, F, solani. Rhizoctonia
olani, Pseudomonas solanacearum (Biovars I
nd II) and a complex of F. solani + R. solani
nd occasionally F. solani + Streptomyces
cables were isolated from diseased tubers. Ex-
ept for F. sambunicum, all pathogens were
consistently present in all survey sites through-
ut the survey seasons. F. solani was more viru-
ent than E. sambunicum. All pathogens caused
extensive rotting in inoculation experiments.
atent infections of these major storage patho-
ens were also observed. Disease incidence was


UAL MEETING OF THE
LOGICALL SOCIETY
YY 3-7, 1988


generally higher during the wet season.
Commonly associated fungi which did not
cause rotting when inoculated alone in intact
tubers included Asperqillus sp., and Penicil-
lium sp. Streptomyces scabies, although fre-
quently observed, was not considered as storage
pathogen since it affects only the skin.

Seaweed (Eucheuma sp.), Sweet Potato (Ipo-
mea batatas Lam.) and Gabi (Colocasiaesculenta
Schott) as Culture Medium Ingredients for
Some Fungal Pathogens. L.B. Montesclaros.
Visayas State College of Agriculture (VISCA)


The suitability of seaweed or "gozo" carra-
geenan as a substitute for commercial agar in
the preparation of culture media for Sclerotium
rolfsii Sacc., Helminthosporium maydis Nish.
Miy., Pestalotiopsis sp., Cercospora henningsii
Allescher, and Sphaceloma batatas Saw. was
examined. The potential of sweet potato and
gabi as substitutes for white potato in PDA with
selected "gozo" carrageenan concentrations was
also determined.
Seaweed carrageenan was found to be an
excellent substitute for commercial agar in the
preparation of PDA and Onion Agar. S. rolfsii,.
fH. maydis, C. henningsii, S. batatas and Pesta-
lotiopsis sp., exhibited the best mycelial
growth in 30, 45, 25, 20 and 45 g/li "gozo"
carrageenan respectively. For good sporulation/
iclerotial formation and high percent spore
germination, 30 g/li "gozo" carrageenan was
superior for S. rolfsii and H. maydis; for S.
batatas, 20 g/li; and for Pestalotiopsis spp.,
40 g/li. C. henningsii, grown in PDA and in
medium with "gozo" carrageenan substitute,
lid not sporulate.
Sweet potato at 300 g/li can replace white
potato in PDA for culturing S. rolfsii while
gabi at 500 g/li can be used for Pestalotiopsis sp.


effect of Nitrogen Application on Rice Blast,
mnd Yield in Upland Rice. E. Kuerschner, M.M.
ramisin, B.A. Estrada, J.M. Bonman, D.P.
'arrity. International Rice Research Institute
IRRI)






Philinnine PhvtoDatI


An experiment at Cavinti, Laguna was cot
ducted to study the effect of timing nitroge
(N) application on blast (Pyricularia oryzae
and yield in upland rice during the 198-7 we
season. The cultivar UPL Ri5 was used to con
pare splits of 90 kg N/ha (early, late, three an
five equal splits) with a control (no N) as sul
plots at two main plot levels (protected, unpr(
tected/inoculated) with four replications. I
unprotected plots, infection on leaves average
9.6% diseased leaf area (DLA) 44 days aftc
seeding,, the peak of the epidemic, and 43'
severe neck blast (SNB) occurred on panicle
Early application, and three or five equally
distributed splits caused high leaf blast infei
tion (11.5, 18.7 and 13.3% DLA). Late applic;
tion of nitrogen resulted in disease leve
(1.4% DLA) comparable to control ploi
(3.2% DLA). Panicle blast (% SNB) was slightly
affected by the treatments. Total dry matt(
reached 5.1 t/ha in unprotected and 5.8 t/ha i
protected plots. Grain yield was significantly
reduced in unprotected plots (1.0 t/ha) con
pared to protected (1.6 t/ha). Nitrogen timing
had a significant effect on % unfilled grair
while number of panicles/m2 and 1000 grai
weight were not affected by the treatment


Effect of Vesicular-Arbuscular Mycorrhia
Fungal Inoculation on Corn and Mungbean. I
R Khadge, L.L. lag and T.W. Mew. IRRI an
UPLB

Field evaluation of vesicular-arbuscula
mycorrhizal (VAM) fungus, Glomus mossea
for crop growth and yield was done in fum
gated and natural soils at IRRI. Corn, IPB Va
1 and mungbean, Var. Pagasa 1 were grown ,
first and second crops, respectively, in fum
gated and natural soils inoculated with Glomz
mosseae. Mycorrhizal inoculation increase
corn yield by 28% and 12% over the uninoci
lated check in natural and fumigated soil
respectively. The inoculation of first crop ha
no significant effect on the yield of the sui
ceeding mungbean crop. Inoculation of tl
mungbean crop with the fungus increased yiel
by 20% over the uninoculated check. The VA]
fungal population in the inoculated corn plo
increased from 12 to 279 propagules per 10
g dry soil in natural soil and from 1 to 221 pri
pagules in fumigated soil. The highest VA]
population recorded in the inoculated mun
bean plot was 188 propagules per 100 g soi
Th* hiohpt nrripntroPy nf rnnt onlnni7~tinn 1


VAM fungus at harvest were 41 and 34 i
mungbean and corn, respectively.


Path Coefficient Analysis on the Effects of
Blast on Rice Growth, Yield and Yield Compe
nents. C.Q. Torres and P.S. Teng. IRRI

Two trials were conducted to determine th
effects of blast on rice growth, yield and yiel,
components. Different levels of epidemics wer
induced by covering some of the plots wit)
plastic sheets at night, applying different
amounts of inoculum, timing of inoculation
and spraying with tricyclazole. Tillers wer
sampled weekly to measure leaf blast severity
plant height and biomass. At harvest, panic
blast incidence was determined and yield corm
ponents were measured. Different epidemi
patterns were obtained in both trials. Path coel
ficient analysis showed that leaf blast has relh
tively stronger negative effect on plant high
than on leaf, stem and panicle biomass. Panicl
blast on the other hand, had a stronger effec
on panicle biomass than leaf blast. Number o
filled grain (NOFG) and 1000 grain weigh
were the yield components almost equally
affected by leaf blast. Percent unfilled grain ((
UG) was affected more by panicle blast than b'
leaf blast. The NOFG and %UG has the highest
direct effect on yield loss in the first and second
trials, respectively. Two equations that woul
predict yield loss (%) at any observed leaf blast
severity (maximum) and panicle blast incident
were developed.


The Effect of Multistress Factors on Diseas
Development in Lowland Transplanted Rici
P.S. Teng, N. Fabellar, T. Woodhead, B.M. ShE
pard, K. Moody, K.A. Gomez, H.U. Neue, K.1
Ingram, L. Estorninos, R. Lantin, E. Pasuquir
E. Rubia, E. Salire, E. Yambao, J. Zamora, an
I. Pangga. IRRI


Potential interactions among water, zinm
stem borer, pathogen, and weed stresses, an
their effects on yield of rice, cv. IR62, wei
studied in a multidisciplinary experimer
during the 1987 wet season. Water stress an
stem borer damage significantly affected th
incidence of some diseases at different growth
stages. Irrigated plots had an average leaf blaj
incidenrp of ?7 4f% which was higher tha


_ ________~__r_______


SO






Jan.& June 1988 Abstracts of Papers


water-stressed plots with 6.14%. Average sheath
rot incidence was 27.01% in plots with simu-
lated stem borer damage which was higher than
plots with stem borer control with 1.31%. Stem
rot incidence of 45.99% was highest in irrigated
plots with stem borer control. The effect of
pathogens decreased the yield by 14%. The
interaction among irrigation, stem borer con-
trol, and pathogen control was significant;
simultaneous implementation of these treat-
ments increased the yield by 4.5 t/ha. Pathogen
control increased the yield both in plots with
stem borer damage and stem borer control, but
there was no significant difference between the
two. However, pathogen control increased the
yield of water-stressed plots by 24 8% and irri-
gated plots by 9 5%. Consequently, water-
stressed plots had 115.0 discolored filled grains/
hill which was higher than irrigated plots with
55.0, while plots with stem.borer damage had
91.0 which was higher than plots with stem
borer control with 79.0


Survival of Rhizoctonia solani Kuhn in Infected
Rice Straws. B.L. Candole and T.W. Mew. IRRI


The saprophytic survival of R. solani, the
sheath blight pathogen, from infected host
tissues of rice varieties with known levels of
resistance to sheath blight, namely: IR64, IR62,
IR58 and IR36 was studied. IR64 and IR62 are
moderately resistant while IR58 and IR36 are
susceptible to sheath blight. Straw pieces mea-
suring 1'inch in length were buried in upland
soils at 50 pcs per treatment. At 2-week interval
for a total of 8 weeks the straws were sampled,
and placed in acidified PDA.
Varietal differences in sustaining the survival
of R. solani were noted. Generally, recovery of
R. solani was negatively correlated, (coefficient
correlation r = 0.48**) with the increase in
T7ichoderma. Such correlation was higher (r =
0.80**) in IR36. Apparently, the straw of IR36
decomposed faster than other cultivars. This
indicates that mycelium survival of R. solani in
infected IR36, which is more susceptible than
others, may not serve as important source of
inoculum. In contrast, IR64 and IR62, which
are less susceptible than IR36 may serve as
more important sources of inoculum due to
slower rate of decomposition. The presence of
Trichoderma in the soil can play an important
rqle in determining the inoculum potential of
R. solani due to its ability to decompose straw.


Effect of Cropping Sequences on Field Popula-
tions of Pratylenchus zeae, Tylenchorhynchus
annulatus and Helicotylenchus crenacauda. T.
Aung, D.M. Matias and T.W. Mew. IRRI

Experimental plots were established from
April 1987 through February 1988 for differ-
ent cropping patterns to investigate the influence
of cropping sequences on field population
dynamics of nematodes associated with upland
cropping patterns. The experimental area was
left fallowed for eight months prior to the start
of the experiment. The first cropping patterns
consisted of;i) sorghum (Sg), ii) Rice (Rc),
iii) control continuous rice (CRc), iv) corn
(Co). In the second cropping patterns, Sg was
substituted with mungbean (Mb), Re was subs-
tituted with Sg, Co was substituted with cow-
pea (Cp), and CRc was repeated as control.
Sorghum, rice and corn after fallow significant-
ly increased the population of P. zeae. T.
annulatus population increased in all cropping
patterns except Co after fallow and Cp after
Co. H. crenacauda population was favored only
by Re or when rice has been a previous crop
but the population increment was not signifi-
cant. "Mb planted after Sg and Cp after Co
significantly suppressed P. zeae and R. annula-
tus population build-up whereas CRc and Sg
after Rc significantly increased their popula-
tion. None of the crops grown favored signifi-
cant increase of H. crenacauda The cowpea and
mungbean cropping patterns were the most
effective for suppressing population build-up
of these nematodes. Corn and rice planted as
mono crop favored rapid increase in population

ofP. zeae.


Simulation of Blast Epidemics Using an Ex-
panded Logistic Model. C.Q. Torres, A.J.P.
Magnaye, P.S. Teng and J.M. Bonman. IRRI

A model that simulates leaf and panicle
blast epidemics was developed by adding in-
creasing complexity to logistic growth function.
It is written in BASIC computer language, made
up of subroutines and a main program. The
components, initial amount of inoculum, plant
age, temperature, dew period, row spacing and
nitrogen applied, "were added to the basic
logistic function (dy/dt = ry (1-y). Results from
the model showed a sigmoid curve which depicts
the different phases of blast epidemic. The
model also estimates the expected yield loss (%)


Jan. & Jine 1988


Abstracts of Papers





Jtj iA


Z ppne yapa oogy *o


based on the simulated leaf blast severity.
(maximum) and panicle blast incidence. The
model will be validated and coupled with the
CERES-RICE model. It will help scientists
understand the interactions of blast with other
production constraints in the field.

SRelationship Among Inoculum Placement,
Type and Density And Their Effect on Inci-
dence and Severity of Sclerotium Foot Rot of
Wheat. D.L. Adorada and A.M. Sinohin, UPLB

Combinations of inoculum placements (sur-
face and mixed), inoculum types (sclerotia,
mycelia and sclerotia + mycelia) and inoculum
densities (2/5, 4/10, 6/15 and 8/20 percent by
weight/sclerotial count) were tested on their
effect on the incidence and severity of Sclero-
tium foot rot of wheat.
Pre-emergence incidence was highest with
mixed inoculum while post-emergence inci-
dence and severity were highest with surface
applied inoculum. In both cases, mycelia alone
were best in initiating infection followed by
sclerotia + mycelia and sclerotia alone.
Inoculum density was significantly corre-
lated with both incidence and severity of
disease.
Among the treatment combinations, 8% by
weight of mycelia alone mixed with the upper
two cm layer of the soil gave the highest pre-
emergence incidence values while placing them
on the soil surface gave the highest post-emerg-
ence incidence and severity values.


Biological Control of Rice Blast Disease by
Seed Coating with Chaetomium. K. Soytong
and T.H. Quimio. UPLB

Chaetomium trilaterale Chivers, C. globo-
sum Kunze and C. cochliodes Pall. isolated
from rice field soils were found to be antago-
nistic to Pyricularia oryzae Cav. on dual agar
culture based either on competition growth or
antibiotic activity.
In greenhouse tests, P. oryzae was grown for
7 days in potato dextrose broth at room
temperature and transferred to sterilized sand-
commeal culture medium (1:10 ratio). After 10
days, it was mixed with either sterilized or non-
sterilized soil before planting. Treatments used
were grouped into sterilized and unsterilized
parts and each further divided into inoculated
--, A -".'- -h-141k.. Un.* A


different seed treatments namely: seed treated
Nith spore suspension of antagonist, culture
iltrate, Captan, and the non-treated. Seeds of
ice variety IR 442-2-58 were used. Treatment
involved five-minute soaking before planting.
Coating the rice seeds with either spore
suspensions or culture filtrate of Chaetomium
spp. and sowing them in soil with P. oryzae re-
sulted in control of early infection, which
otherwise often results in aborted seeds. This
indicates that an antibiotic substance that
effectively hampers development of the
pathogen may be produced by Chaetomium.
The antagonist-coated seeds also had increased
shoot emergence which resulted in better plant
height and root growth, and gave greater fresh
weight of plants. All these were also observed
when the seeds were treated with Captan.
The above preliminary trials suggest that
once certain strains of Chaetomium are esta-
blished in the soil, rice seedlings may be pro-
tected from early infection by P. oryzae.


Bacterization of Rice for Biological Control of
Fungal Pathogens. S.S. Gnanamanickam, B.L.
Candole, A.M. Rosales and T.W. Mew. IRRI

Twelve fluorescent and 7 nonfluorescent
bacterial strains that exhibited in vitro anti-
biosis towards Sclerotium oryzae, the stem !rot
pathogen, were evaluated in field experiment
during wet season 1987 in lowland rice fields
at IRRI farm. IR20 seeds were bacterized by
soaking in bacterial cell suspension (107 cfu/
ml) for 12 h at 25 C. After incubation for 24 h,
bacterized and non-bacterized seeds were sown
in seedbeds. Twenty-one-day-old seedlings were
transplanted in 8 replicate plots (3 x 3 m) each.
Four plots received 5 additional ,bacterial
sprays at 20, 25, 40, 55 and 70 days after
transplanting. IR20 plants, that received addi-
tional bacterial sprays yielded an average of
2.53 t/ha in comparison with 1.45 t/ha of non-
treated plots, while grain yield of plants raised
from bacterized and non-bacterized seeds were
1.39 and 1.00 t/ha, respectively. Grain yields
were not significantly different for the various
strains used. Significant stem rot suppression
was observed between treated and non-treated
plants. Five sprays of isolate In-b-104 provided
the most effective control of stem rot, while
seed treatment alone with isolate In-b-1753
effectively reduced sheath rot incidence. Seed
treatment combined with bacterial sprays re-
__1- -1- 1 - A *'_- 1L -r L -


ilih i Ph t th l






An k IT.- 1QOO


and narrow brown spot severity. Thus, this
study shows the potential of bacteria as biocon-
trol agents of rice fungal diseases in field con-
dition.


Potential of Solarization and Surface Firing in
the Control of Plant Parasitic Nematodes. E.B.
Orolfo and R.G. Davide. UPLB

A study was conducted to evaluate the effi-
ciency of solarization (covering pre-irrigated
soil with clear polyethylene plastic sheet and
exposing it to the sun's radiation) and surface
firing (burning of rice straw on the soil surface)
to control plant parasitic nematodes, mainly
Rotylenchulus reniformis, Meloidogyne incog-
nita, Hemicycliophora sp. and Helicotylenchus
sp. Results showed that 20-day solarization
significantly reduced the nematode population
(88.7% 1 month after treatment and 52.8% at
harvest). This was comparable with the nemati-
cide treatment (Nemacur 10G) which reduced
nematode population by 75% 1 month after
treatment and 58.8% at harvest time. It was
further observed that solarization effectively
controlled weeds while surface firing improved
the physical and chemical properties of the soil
as indicated by increased amount of organic
matter (OM) and NPK resulting in a 54.7%
increase in yield over the control.


Efficacy of Fungicides on Hybrid Rice Seed
Discloration and Seed Infection. S. Merca, D.
Matias, C. Huelma, T.W. Mew and S.S. Virmani.
IRRI

Daconil, Bas 346 and Benlate plus Dithane
M-45 were used at recommended rates in 2
spray schedules in hybrid rice plants to evaluate
their effects on seed infection and seed discolo-
ration using 2-factor RCBD. IR54752A and
ARC 11353R were used during the regular wet
season planting in June 1987. The 2-spray sche-
dules were a) application of sprays 2 weeks
before booting, and b) application at booting,
both followed by weekly sprays thereafter. The
second spray schedule significantly reduced
seed discoloration on R lines but not on A
lines. Based on standard blotter test results for
seed borne organisms, the 2-spray schedules
were not significant, but the fungicides lowered
significantly the incidence of the following seed-
borne organisms; Trichoconis padwickii,


Mn A and R lines. The fungicides were observed
:o increase significantly the incidence of Curvu-
aria spp. Bas 346 was observed more effective
against the majority of the seed borne fungi
encountered in the tests than Benlate plus
Dithane M-45, while Daconil had the least
effect.


reaction of Ten Corn Cultivars/Lines to Five
solates of Erwinia carmotvora var. chrysan-
hemi causing Stalk Rot. G.N. Bastasa and R.
4..Gapasin. ViSCA

This study was conducted to determine the
action of ten corn cultivars/lines, namely,
'amotes Tiniguib, Native Pilit, Population 25,
populationn 30, IPB Var 2, Tropical Early White
Flint, MIT Var 2, Improved Tiniguib, ViSCA
Composite and Super Sweet Corn, to isolates of
.rwinia carotovora var. chrysanthemi causing
talk rot obtained from Tranca, IPB-UPLB,
JSM, Banga and ViSCA.
Of the ten cultivars/lines tested, Population
10 was found to be resistant while the rest were
susceptible with Improved Tiniguib being the
nost susceptible. Among the isolates used, the
langa isolate was found to be the most virulent
>ased on infection and toppling of the cultivars
mnd lines. The ViSCA isolate was the least
'irulent.

lace-Specific Partial Resistance to Blast in
'emperate Japonica Rice Cultivars. J.M. Bon-
nan, Y.H. Lee, E.J. Lee, B. Valent and J.M.
landong. IRRI

The resistance of Korean indica and japonica
ice cultivars to rice blast was assessed in field
rials in Korea and in the Philippines. Indica
ultivars were completely resistant in the Korea
rial, but showed varying levels of disease in the
'hilippines. Many of the japonica cultivars
vere qualitatively susceptible in both countries
nd most showed higher degree of disease in
Lorea. Tests with Korean and Philippine isolates
if Pyricularia oryzae indicated that the dif-
erential response between trial sites of these
aponica cultivars was due to race-
pecific partial resistance.


:valuation of Resistance of Selected Rice
varietiess to Bacterial Leaf Streak. E.S. Medalla,


. .





Philippine Phytopathology


Screening and evaluation studies were done
to determine the resistance of rice vageties to
bacterial leaf streak. Among the 303 naturally-
infected upland rice varieties, 27 have 5% or
less leaf area infection, while 3 varieties, name-
ly: Agulinha Branco, Iniap 415 and Bolibod
Natural were found to be highly susceptible at
seedling than at maximum tillering stage.
Variety CNA 4206 on the other hand, showed
the lowest infection except with isolate 127 at
the seedling stage.


Disease Reaction of Philippine Traditional Rice
Varieties. T.U. Dalisay, A.M. Sinohin and D.B.
Lapis. UPLB

Forty-three upland and 577 lowland tradi-
tional varieties were screened against rice
diseases during the 1987 dry season and 1988
wet season.
Induced method of evaluating upland
varieties showed that Palikero, Buluhan, Sang-
lay, Awot, Macan, Kumpol, Wagwag, Binikol,
Kinandang Pula, Sinaging and Malagkit Tagalog
were consistently resistant to rice blast and
sheath blight while Ninakar, Binanar, Enito,
Initlog, Malagkit, Dinorado, Pinursige (Puti),
Binabae, Benzer and Wagwag were rated resist-
ant to bacterial blight. Palikero and Initlog
Dalag were intermediate to ragged stunt virus.
Only B-10 showed resistant reaction to
tungro virus complex. Variety Azucena exhibit-
ed resistance to rice blast and sheath blight and
intermediate to ragged stunt virus.


Two Types of Inclusions in Grassy Stunt Virus-
Infected Rice Cells. F.C. Sta. Cruz, H. Hibino
and V. M. Aguiero. IRRI

Ultrathin sections of grassy stunt virus
(GSV) -infected rice leaves were
examined under the transmission electron
microscope. Two types of inclusion bodies were
observed. A filamentous inclusion was observed
in the mesophyll and vascular bundle cells but
not in similar cells of healthy and rice tungro-
infected plants. The inclusion consisted of fine
filaments arranged in a paracrystalline array. It
was either free in the nucleus or cytoplasm, or
bounded with membrane in the cytoplasm.
Similar inclusions were also found within the
vacuole in sieve tubes and consisted of tubules
associated with particles about 18 nm in


diameter. Similar structures were not observed
in healthy and tungro-infected plants. The
occurrence of tubular inclusions was less
frequent than the filamentous inclusion in
GSV-infected plants.


Stem Rot of Ramie Boehmeria nivea (L.) Gau-
dich) in the Philippines. T.O. Dizon, TT.T
Reyes, J. San Pedro and R.P. Cabangbang.
UPLB

A new disease of ramie, named stem rot, was
observed and reported for the first time in the
Philippines. The disease is caused by a fungus,
Corticium rolfsii Cursi.
Symptoms of the disease were wilting and
watersoaking of the basal portion of the plant.
Severely infected plant turned brown, defoliat-
ed and ultimately died. Profuse white mycelia
of the fungus covered the infected stem.
The fungus produced abundant mycelia on
various agar media except on glycerine agar,
sweet potato agar, pechay agar and water agar.
Good mycelial growth was noted at 25, 30 and
35 C, with maximum growth at 30 C. At 40 C,
mycelial growth was completely inhibited.
Continuous light, continuous dark and alternate
light and dark supported abundant mycelial
growth of the fungus. Longer exposures to
ultraviolet light (16 hours and 24 hrs) sup-
pressed growth. The fungus did not produce
fruiting structures on agar medium but formed
basidiocarp on sterilized inoculated stem
tissues. The fungus has a wide host range.
Of the six inoculation methods evaluated,
inoculation at the base of the stem, inoculation
of the injured stem 5 cm and 10 cm above soil
surface showed the symptoms of the disease. Of
the 48 ramie lines and varieties screened against
the disease, 1 was found resistant and 2 were
moderately resistant.


Occurrence, Symptoms and Host Range of Pea-
nut Stripe Virus. F.L Mangaban and M.P.
Natural. UPLB

The occurrence of peanut stripe virus (PStV)
in the Philippines was first reported in 1984.
Recent surveys showed that PStV is no longer
confined to experimental areas. The disease is
observed in farmer's fields, particularly in
Southern and Northern Luzon.
The disease is characterized by continuous
striping, presence of green islands or blotches,


Vol. 24






Abstracts of Iapeu b3


nd/or oak-leaf pattern in peanut. Host range
studies revealed that it can systemically infect
Wlycine max and induce local lesions in
'henopodium amaranticolor and C quinoa but
iot in Phaseolus vulgaris. PstV is observed to be
transmittedd by the black bean aphid, Aphis
:raccivora, in a non-persistent manner.

rin Selection Methods for Plant Growth-
'romoting Rhizobacteria. A.M. Rosales and
r.W. Mew. IRRI.

A blotter method was developed and its
efficiency was compared with 2 other methods
- inhibition of mycelial growth and reduction
f sclerotial germination tests, for screening of
)lant growth-promoting rhizobacteria (PGPR)
n vitro. Twenty-three bacterial strains and four
R rice cultivars IR36, IR42, IR58 and IR64
vere used. Seeds were bacterized by soaking in
bacterial cell suspension (107 cfu/ml) for 10
nin. Twenty-five: seeds were arranged in each
if four petri. plates with moistened filter paper
n incubated for five days at 28 C with conti-
uous fluorescent light. Varietal differences in
:rms of percent germination, radicle and shoot
measurements in response to seed bacterization
ras observed by blotter method. Germination
f IR58 and IR64 was enhanced from 78 to
3% and from 89 to 97%, respectively, when
acterized with species of Bacillus and Entero-
acteriaceae. These strains also induced strong-
r inhibition of mycelial growth and reduction
if sclerotial germination of R. solani, indi-
ating that blotter method when used in com-
ination with other techniques is an efficient
method for selection of PGPR strains.


Jse of Biotin-Labelled Probes in the Analysis of
Canthomonas campestris pv. oryzae Genomes.
I.T. Chua, E.Y. Ardales, and H. Leung. IRRJ.

Radioactive labelling of DNA probe is an
indispensable tool for the identification of
specific DNA sequences in the genomes of plant
pathogens. Due to difficulty in obtaining a reli-
ble supply of 32p-labelled nucleotides (with a
hort half-life of 2 wk), the use of a non-
adioactive labelling technique with biotiny-
ited nucleotides was explored. This technique
xploited the high affinity between biotin and
vidin (or streptavidin) such that biotinylated
)NA molecules could be coupled to biotiny-
ited alkaline phosphatase using avidin/strepta-
idin as an intermediate. Hybridized DNA


equences were revealed by a color reaction
betweenn alkaline phosphatase and chromogenic
ubstrates. Using nick-translation, DNA
equences from X. campestris pv. oryzae (Xco)
vere labelled with biotinylated deoxyribo-
nucleotides and used to hydridize with genomic
)NA digested with restriction endonucleases.
Southern blot analysis showed that biotinylated-
'robes could detect DNA polymorphism in
various X. campestris pathovars. The same
liotin-labelled probe was found to be sensitive
enough to differentiate Xco from other patho-
ars of X. campestris in dot blot analysis.
Results suggest that biotin-labelling can serve as
n alternative to radioactive labelling in mole-
ular analysis of pathogen genomes.

enzyme Polymorphism Among Pyricularia
ryzae Isolates from Rice and Weed Hosts in
he Philippines. M.A. Bemardo, E.S. Borromeo
nd H. Leung. IRRI

Enzyme polymorphism of P. oryzae isolates
rom rice and grass hosts using starch gel
lectrophoresis was examined to understand the
enetic structure of P. oryze population in the
hilippines. Fifty rice isolates from Tarlac,
Wueva Ecija, Camarines Sur, Palawan, Misamis
rentala, Cavinti, Pampanga, Zamboanga and
'avite and 13 nonrice isolates from grass hosts
rere analyzed for electrophoretic variation in 8
nzymes: phosphoglucomutase (Pgm), phos-
hoglucose isomerase (Pgi), malate dehydroge-
ase (Mdh). lactate dehydrogenase (Ldh)
lutamic dehydrogenase (Gdh) glycerate-2-
ehydrogenase (G2dh), xanthine dehydroge-
ase (Xdh), and 6-phosphogluconic dehydroge-
ase (6 Pghd). All 50 rice isolates were mono-
iorphic at all enzymes tested. Of the 13 non-
ice isolates, 7 had a functional allele and 6 had
null allele at the Ldh 1 locus. At Ldh3, 9 had
fast allele and 3 had a slow allelel. One isolate
rom Panicum repens L had a new fast variant
t Ldh3 and a slow variant at G2dh. The differ-
nt alleles found in rice and nonrice isolates can
e used as natural markers for studying mecha-
isms of variation of the fungus.


cultural Physiological and Pathogenic Varia-
ions in Cercospora Canescens, Causal 'Orga-
ism of Mungbean Leaf Spot in the Philippines.
.L. Mangaban ang M. P. Natural. UPLB

Eight isolates of Cercospor canescens,


Abstracts of Papers


63









a auzcu iu51.5 Us slIUiusMA a,& OW yv.* w .
collected from different mungbean *growing
areas of the country.
Differences in colony size and color, in vitro
sporulation capacity and discoloration of
potato dextrose agar (PDA) were noted. Uke-
wise, the differential effects of these isolates on
resistant and susceptible mungbean lines were
determined based on the following parameters;
latent period, size and growth of lesion, infec-
tious period and sporulation capacity. Culture
filtrates were extracted and bioassay test was
conducted to determine their effect on seed
germination and root elongation of mungbean.
Isolate MCO exhibited the biggest colony
size but isolate MCS produced the highest
number of spores per ml of fungal suspension at
7 and 14 days after incubation.
Differential aggressiveness was noted among
isolates. Isolate MCB produced the earliest
lesion on susceptible and resistant lines at 2 and
7 days after inoculation, respectively. MCPS
produced the biggest lesion on susceptible and
resistant lines.
Based on root growth bioassay, MSDB did
not adversely affect root growth of mungbean
but culture filtrates of MCPS inhibited seed
termination and root elongation of mungbean


or wav ... ..ut & u Meta uj w T. V TVW.W
after storage at moisture contents of 9.3 -
18.33%. The percentage germination of paddy
remained higher when stored at moisture
contents of 9.3-14.0% but decreased with
storage time at 14.5-18.3% moisture content.
The percent germination of paddy reached i
peak at 10-15 weeks of storage and decreased
gradually thereafter. A significant negative cor-
relation between percent germination and
moisture content was observed.


Leaf Blast Development and Leaf Wetness in
Two Upland Rice Cultivars. I. Schloesser, J.M,
onman and J. Kranz,

Aside from host resistance, the plant type ol
a cultivar may influence blast development by
affecting the micro-climate. To determine the
effect of plant type on leaf wetness and devel.
opment of blast caused by Pyricularla oryzae,
field experiments were conducted in the dry
and wet season 1987 using Lubang, a tradition.
al, droppy-leaved cultivar, and C22, an improve.
ed cultivar with erect leaves.
I of CIl Pt inCratin .I.. me I,.ar in thl ,A4i


wetness durat


Paderes, L.L. Ilag and T.W. Mew. IRRI

The relationship of moisture content and
storage period to fungal population and seed
germination was studied.
Various fungal species predominated at dif-
ferent moisture conditions and storage periods.
The fungi observed were Aspergillus flavus-
oryzae, A. glaucus, A. nidulans, A. candidus, A.
versicolor, A. terreits, A. niger and unidentified
species of Penicillium, Tichoconiella, Curvu-
laria, Fusarium, Syncephalastrum, Verticillium,
Cladosporium and Rhynchosporium. The
predominant storage fungi were A. flavus-
oryzae, A. glaucus and A. candidus whereas the
predominant field fungi were Trichoconiella
sp., Cunularia sp. and Syncephalastrum sp.
A decrease in the number of field fungi and
an increase in the number of storage fungi with
storage time was observed.
Storage fungi from the wet and dry season


caused.


Effect of NPK and their Combinations on the
Occurrence and Severity of Stalk Rot on Corn.
T.B. Bayaron. USM

The highest percentage infection of stalk rol
on corn in single element application waj
observed in plots treated with nitrogen at the
rate of 120 kg/ha. This was followed by potas.
sium. but at its lower rate of 30 kg/ha. The
addition of phosphorus decreased infection
which was comparable to untreated plots.
For two elements combined such as NP, NK,
and PK, severe infection of stalk rot was
observed in plants treated with the NK combi.
nations. In the NP combinations, stalk rol
infection was low compared with the NK bul
higher if compared with the PK combinations,
The lowest infection of stalk rot was obtained


__









JLJnl1 UIL rt l. %uIIumIUiaUI uI. UIUI s l lnt ratu uI
90-90 kg/ha.
In the N,P, and K combinations, the infec-
tion of stalk rot was low when nitrogen was
applied at the rates, of 60 and 90 kg/ha but not
when the rate was increased to 120 kg/ha.
Increasing the rate of phosphorus, however, to
90 kg/ha gave a lower infection. From these
results, it could be deduced that maintaining a
high level of P with medium levels of N and K
would minimize stalk rot in corn fields.
Significant increase in yield was observed
from plots applied with N and more so when
combined with P and/or K. The highest yield,
however, was obtained from NPK-applied
plots. Further, increasing N from 60 to 120
kg/ha had correspondingly increased the yield
of corn.
Yield loss due to stalk rot infection ranged
from 15 to 49%. The application of N alone or
in combination with P and/or K increased stalk
rot infection but likewise increased yield of
corn thus losses due to stalk was reduced.
However, no significant differences were
observed among the treatment combinations.


Feeding Mode and Tungro Transmission Effi-
ciency of Green Leafhopper Colonies Selected
on Resistant Cultivars. G. Dahal, V. M. Aguiero,
and H. Hibino. IRRI

A green leafhopper (GLH) Nephotettix
virescens population collected from South
Cotabato was reared on GLH-resistant cultivar
IR64 for 7-9 generations. Thereafter the IR64
colony was maintained for 6-12 generations on
GLH-susceptible TN1; moderately resistant IR-
26 and IR36, and resistant IR54 and IR 64. A
GLH colony maintained on TN1 for many
years served as the control These colonies were
tested for their tungro transmission efficiency
and feeding behavior. Tungro-viruliferous adult
GLH were allowed to feed individually for one
day on 7-10 day-old seedlings of IR26, IR36,
IR54, IR62, IR64, and TN1. Their mode
of feeding was monitored by color reaction of
honeydew spots excreted during the feeding on
bromocresol green-treated paper discs placed at
the bottom of seedlings. Blue spot indicates
phloem feeding and brown or orange spot
indicates xylem feeding. Seedlings were indexed
by latex serology or ELISA for the presence of
rice tungro bacilliform virus (RTBV) and rice
tungro spherical virus (RTSV).


S Mode of feeding and virus transmission on
test cultivars varied depending on GLH colonies
used. Original IR64 colony transmitted pre-
dominantly both RTBV and RTSV on IR64
and TN1, while TN1 colony transmitted pre-
dominantly RTBV alone on IR64 but both
RTBV and RTSV on TN1. During the inocula-
tion feeding on IR64, IR64 colony fed more on
phloem than TN1 colony did. IR64 colon)
maintained on IR26, IR36, IR54, and IR64
transmitted more efficiently both RTBV and
RTSV on all cultivars; except on IR62. The
four colonies did not show much difference in
their feeding mode and virus transmission
efficiency on the test cultivars. IR64 colony
maintained on TN1 fed more on xylem and
transmitted predominantly RTBV alone on
resistant cultivars as did TN1 colony. On
IR26, all colonies tested transmitted RTBV
alone. On IR62, all colonies predominantly
transmitted RTBV alone and fed mostly on
xylem. These results indicate that GLH colonies
quickly change their transmission efficiency
when maintained on susceptible cultivar but
not on GLH-resistant cultivars.


Comparison of Methods for Monitoring Green
Leafhopper, Nephotettix virescens (Distant),
Feeding During Tungro Transmission. G. Dahal,
H. Hibino and R.C. Saxena. IRRI


Honeydew tests using bromocresol,
ninhydrin, or safranin dye and an electronic
device for monitoring feeding of
S viruliferous N. virescens adult during inocula-
tion access and transmission of rice tungro
bacilliform (RTBV) and rice tungro spherical
(RTSV) viruses in seedlings of susceptible and/
or disease-resistant rice cultivars were com-
pared. Inoculated seedlings were indexed for
virus infection by ELISA. Electronic recording
and bromocresol tests were effective for deter-
mining the relationship between feeding sites
and virus transmission. The ninhydrin test can
be used for monitoring phloem feeding, but not
for non-phloem feeding. The safranin test
accurately determined xylem feeding, but only
one or two individuals could be tested at a time
with one recorder. The bromocresol method
could be used for motoring feeding by many
individuals simultaneously, but it was less
accurate because the honeydew spots excreted
on the filter paper disks overlap occasionally.


Ig U dUUA 1JV


....... , '* wa






Philioine hvtnathnlev -


Detection Method of Aphelenchoides besseyt
for Routine Examination of Rice Seedlots.
E.B. Gergon and T.W. Mew. IRRI

Different methods of detecting Aphelen-
choides besseyi in rice grains were evaluated
for use in routine seed analysis involving
large number of seedlots.
The highest number of A. besseyi was
detected in 24 hours by manually separating
the hulls from the kernel. This technique, how-
ever, is time-consuming. The other methods
which used Baermann funnels or sieves in a dish
gave lower detection rate but their use could be
made feasible for routine examinations by
extending the extraction period. Nematodes
from pre-germinated or dry seeds may be col-
lected after 48 to 72 hours to obtain a higher
nematode recovery.
The highest percentage infestation of 79.3%
was obtained from deformed grains. The
highest nematode count detected was 121 and
the mean was 21 per seed.


Rice Seed and Seedling Inoculation in Relation
to Sheath Rot Transmission. S.P. Milagrosa and
J.M. Bonman. BSU and IRRI

Infection of Sarocladium oryzae was observ-
ed at all stages of rice growth, and as early as 5
days after sowing in untreated and hot water-
treated seeds. Thus, infection by S. oryzae
occurs earlier than the reproductive stage, when
obvious sheath rot symptoms appear. Injection
of spore suspension resulted in leaf sheath
browning 2 weeks after inoculation. However,
both spraying and injection of inoculum gave
the maximum disease incidence at maturity.
In general, at early stages of plant growth there
was less infection of S. oryzae on plants raised
from hot water-treated seeds in a greenhouse
but, as the plants approach maturity, the per-
centage infection between untreated and hot
water-treated seeds did not differ. In field
experiment, a sudden decrease of S. oryzae in-
fection was observed. This was probably due to
senescence of the initially infected leaf sheaths.
The infection of the leaf sheath increased from
seedling stage to maturity.


Evaluation of Species of Saccharum and
Erianthus Against Sugarcane Smut Caused by


Ustilago Scitmninea Sydow. M.M. Guevarra.
SRA

Two hundred sixty-nine accessions of Sac-
charum spp. and Erianthus spp. collected from
different parts of the Philippines were screened
for their reaction to sugarcane smut caused by
Ustilago scitaminea Sydow.
Of the 178 S. spontaneum accessions tested,
104 were susceptible (S) to very highly suscept-
ible (VHS), 27 were intermediate susceptible
(IS) to intermediate resistant (IR) and 47 were
resistant (R) to very highly resistant (VHR). Of
the 59 S. officinarum tested, 22, 11 and 26
exhibited S to VHS, IS to IR and R to VHR
reactions, respectively. All accessions of S.
robustum and Erianthus spp. had VHR reac-
tions.


Evaluation of Species of Saccharum and
Erianthus Against Sugarcane Downy Mildew
Caused by Peronosclerospora philippinensis
[ (Weston) C. G. Shaw]. R.C. Sampang. SRA

Two hundred sixty-three accessions of Sac-
charmn spp. and Erianthus spp. collected from
the different parts of the Philippines were
screened for their reaction to sugarcane downy
mildew caused by Peronosclerospora philip-
pinensis (Weston) C.G. Shaw.
Of the 190 S. spontaneum accessions tested,
173 were resistant (R) to very highly resistant
(VHR), 7 were intermediate susceptible (IS) to
intermediate resistant (IR), and 10 were suscep-
tible (S) to very highly susceptible (VHS). Of
the 53 S. officinarum accessions tested, 41,9
and 3 exhibited R to VHR, IS to IR and S to
VHS reactions, respectively. Three R to VHR
and 1 IS were obtained among S. robustum
accessions. All Erianthus spp. exhibited R to
VHR reactions.


Sclerotium Wilt of Peanut. L.D. Valencia and
M.P. Natural. UPLB

Sclerotium wilt caused by Sclerotium
rolfsii Sacc. in peanut was found to be more
prevalent in the field during wet season. The
diseased plants exhibited yellowing and wilting.
White mycelia and sclerotia were also seen on
affected plant parts.
Preliminary greenhouse screening of 94
Deanut lines showed that three lines did nnt


. ..


PhilinDine Phvtooathnovli






Fan. & June 1988 Abstracts of Papers


succumb to the disease while four exhibited
moderately resistant reactions.

Moderate Resistance of Selected Rice Varieties
to Bacterial Blight. R C. Reyes, S.H. Choi,
K.S. Jin, E.J. Lee and T.W. Mew. IRRI

Selected varieties were tested at seedling,
maximum tillering and flagleaf stages using six
isolates of Xanthomonas campestris oryzae in
Korea. Fourteen varieties showed strong and
weak interactions with six bacterial blight
isolates at three stages. Minor differences were
shown among different variety-isolate combi-
nations especially at later stages. Majority of
the varieties used were japonica type which
probably have adult plant resistance. However,
the differences indicate strong interaction
among fourteen varieties and six isolates in
Korea based on 2 variety-2 isolate combinations
at maximum tillering stage. Inoculation at later
stage, showed decreased lesions indicating
increase in moderate resistance, thus differences
in interaction were no longer apparent. Mode-
rate level of resistance to bacterial blight ap-
peared to be common among the varieties.


A New Mass Screening Method for Rice Sheath
Blight Resistance. RC. De la Pena, S.W. Ahn
and T.W. Mew. IRRI

A new mass screening nursery method under
rainfed upland condition was developed. The
condition enhances inoculum efficiency, uni-
form distribution of inoculum and easy plot
management including manipulations of micro-
climate variables of the nursery. Studies at
IRRI showed that disease severity under upland
condition was highly correlated with that
observed in lowland. However, the incidence of
sheath blight was significantly higher under
upland condition. In the new system, nursery
plots are uniformly prepared and canals are
constructed at the sides for drainage. Each test
entry is directly seeded into two 50 cm rows
with 5 hills per row and spaced 10 cm and 20
cm between hills and rows, respectively. Wind-
hrolre 2orp nrnwvirpcl iieina mndlpratplv rp.citant


Two sorghum lines Ace I and BTx 624 were
used to assess yield components and reduction
in yield due to Rhizoctonia sheath blight. This
disease caused 35% and 42.5% yield loss, re-
duced 100-grain weight by 49 and 57% and
decreased seed size by 20 to 28% in Ace. 1 and
BTx 642, respectively. Number of grains per
panicle was not affected.
Leaf sheath inoculation was the most suit-
able technique in screening sorghum for resist-
ance to Rhizoctonia sheath blight under field
condition. Results from laboratory method
using detached leaf inoculation were similar to
field reaction.
Out of 1443 breeding lines and accessions
screened from 1978-1986, 6 were identified as
resistant to Rhizoctonia sheath blight.


Estimation of Rice Yield Loss Caused by
Tungro Using Modified-Single Tiller Method.
F.L. Nuque, A.J.P. Magnaye, C.S. Salamatin
and P.S. Teng. IRRI

The quantitative relationship between
tungro virus infection and yield components of
rice was evaluated using a modified single tiller
approach. Results showed that yield losses per
hill and per panicle varied depending upon
symptom severity and height reduction of
tungro-infected IR64 plots. Losses ranged from
1.1-99.1% per hill and 1.0-96.1% per penicle.
Losses in 1000 grain-weight ranged from 13.5
to 57.8%. Filled grain percentages were higher
in healthy than in infected plants. Yield loss per
hill and per panicle was positively correlated
with height reduction and symptom severity.
Height reduction and symptom severity were
significantly correlated with biomass. Regres-
sion equations were developed with different
combinations of dependent and independent
variables.


Screening of Different Fungicides Against
Fungal Pathogens of Cotton L. Cantos-Cano.
CRDI

Five fungicides, using the manufacturer's
rpt-nmmpnnlpd ratpq prp c rPrPnped roainct


under greenhouse condition using the seed-
Evaluation of Resistance and Yield Loss in soaking method.
Sorghum Due to Rhizoctonia Sheath Blight. Results showed that percentage damping-
C.B. Pascual and A.D. Raymundo. UPLB off caused by R. solani ranged from 85.3% to


[an. & June 1988


Abstracts of Papers











%. season trial.
amping-off infection caused by S. rolfsij in The rate of increase in lesion length/w
treated with different fungicides at various was significant in 7 cultivars in the dry sea
entrations ranged from 16.3% to 49.3%. trial and in all cultivars in the wet season ti
ocide 50 WP at levels 0.5 g/li and below, It differed among cultivars and between seas
sate 200 at 2.0 g/li and 1.0 g/li and Cobox where the rate during the wet season was hig
at 2.0 g/li were likewise effective against than during the dry season in each cult:
pathogen with a percent control of 49.4% which was positively correlated with les
t.5%. length. The rate of disease increase was p
tively correlated with lesion length in b
seasons.
nation of Corn Cultivars and Assessment Percent loss in grain yield, based on 20
fieldd Loss Due to Banded Leaf and Sheatl fected plants/plot in the wet season tl
it. I.B. Pangga and M.P. Natural. UPLB ranged from 4.9-18.2%. Cargill 5402, SMC
VISCA 8341, and SMC E2 had high perc
twenty corn cultivars were evaluated for yield losses. These were the only culti,
:ance to banded leaf and sheath blight where significant difference between the c
:d by Rhizoctonia solani f. sp. sasakii. trol and inoculated treatments were obser
g lesion length as basis, some cultivars Percent loss in grain yield was not correlh
identified as resistant. Pioneer hybrids with lesion length and rate of disease incrn
istenly produced the shortest lesion lengths in the wet season trial.
te dry and wet season trials. Cargill 5401 Analysis of 1000-kernel weight did
5402 gave long lesions in both trials. Inter- detect significant differences between the c
ate lesion lengths were observed in IPB X trol and inoculated treatments in both seas<
IPB VAR 2, and others. Differences in



POSTER PRESENTATIONS



I Detection of Coconut Cadang Cadang. the disease to the north is in Magsikap, Gen
i. Rodriguez, M.T.R. Ignacio and LP. Nakar, Quezon and to the south in Homon
>ko. PCA Is., Guiuan, Eastern Samar, only 50 km fi
the tip of Dinagat Is., Surigao del Norte. '
rapid, cost-saving and reliable field assay causal organism, coconut cadang-cadang vii
lique was developed and a mobile labora- (CCCV) has been detected in naturally-infec
was constructed for conducting extensive coconut, oil and buri palms in the Philippine
ng-cadang epidemiological surveys, well as in coconut with tinangaja disease
he technique involves a two-step extraction Guam. Recently, CCCV was detected in c<
ie viroid from leaflets and its visualization nut and oil palms from Solomon Is. This is
polyacrylamide gel electrophoresis-silver first report of the viroid outside the Philipp
te staining. Guam region.
The disease is rarely seen on palms be:
ad and Distribution of the Coconut they commence bearing nuts and incide
mg-Cadang. E.P. Pacumbaba, J.C. Orense increases more or less linearly with age.
I.B. Zipagan. PCA rate of increase in the number of diseased pa
range from 0.26% to 1.32% per annum in











ns with CCCV is the reservoir of inoculum. dence gradually increased up to 29 days
transplanting and then decreased as a res
increased infection with both RTBV
Incidence of Phytophthora Disease of RTSV.
onut at the Albay Research Center. E.P.
o and M.B.F. Paloma. PCA ,/Rice Stubbles as a Source of Tungro
7N Z.M. Flores, E.R. Tiongco and H. Hibino.
From 1983-1987, daily monitoring of the
rtophthora disease of coconut was done in Rice stubbles of IR64 and TN1 variety
i areas at the Albay Research Center planted the field infected with both RTBV and 1
Cameron Red Dwarf (CRD), Malayan were used as virus sources two weeks
low Dwarf (MYD) Malayan Red Dwarf harvest. Virus-free male green leafho
ID), Catigan, Tacuman, Malayan Yellow (Nephotettix virescens Distant) reared on
arf x West African Tall (MYD 'x WAT), plants for many generations in the green]
aeron Red Dwarf x West African Tall (CRD were introduced on caged-and uncaged-stul
JAT\ Ci..nr-ii fr.oo, nt.,'rf v Wpr t Afri. The following day. leafhoppers were coll


all (NRM x WAT

e of disease among
significantly dif
t of Catigan, Tact
ll'r AI T Ar'F v II


Laguna and L11"11 iUticULIV1Ly. liallUipplIV pVt,;1 uII..
N. virescens were also collected by swe4
on one and 4-week old stubbles and test
'CRD, MD, their infectivity.
*rent at 1% ., ar ..'. .


1, WAT, EGD A U A IR64. Most leafhoppers transmitted i
T, and Tagnanan was significantly different RTBV and RTSV together or RTBV
5% level. Only Laguna was resistant to the Leafhopper species collected from IR64
!ase with only one palm infected during the bles by sweep net were not infective for
year observation period. The disease was RTBV or RTSV and those from TN1 stA
nd to be highly correlated with rainfall, were infective but at low levels.


igro-Infectivity of Field-Collected Nepho- Expert Systems in Rice Disease Manageme
ix virescens Distant. E.R. Tiongco, Z.M. Computer-Based Decision Aid. N.G. Fabel
res, and H. Hibino. IRRI and P.S. Teng. IRRI

Experiment was conducted in a tungro field A prototype of an expert system, DIS
m September to November 1987. Green- was developed for two (2) major rice dis
hoppers (Nephotettix virescens) were col- tungro and blast. DISMAN is aimed at pi
ed by aspirator in the rice cultivar TN1 at ing the intended end-user a computer-
erent times after transplanting and indivi- decision-aid and a learning experience in d
Uy tested for their infectivity on TN1 seed- management. The intended end-users an


d seedlings we
i and indexed
RTBV and RTS
dence was mor
C. E DrPr


:sence database, knowledge base (Rul
ungro reasoning, while the inferencinj
id the built into the Expert shell called
ed hv ThArp arm thrPe () rdatahames: (i~


A hiohar nerrcntaop of /V vire.cen trans- which include the follow






70 Philippine Phytopathology Vol. 24


ant driving parameters for the tungro module also monitored. Disease progress for both
include the culture types (lowland (irrigated/ planting methods followed the logistic curve.
rainfed) and upland), crop stage, variety, plant. The spatial distribution pattern of diseased
ing method, the number of times the particular plants changed as the disease progressed. A
variety was planted, vector population and random pattern was detected early in the season,
history of tungro epidemics. The blast module followed by a clustered pattern and finally by
includes the following parameters; culture a regular distribution late in the season. The
type, variety, rate of nitrogen application, degree of clumpness decreased as the disease ap-
crop stage, season, rainfall pattern/frequency, preached a regular distribution as indicated by
and amount of disease at particular stage. the increasing k-values. K-value is the clumping
Further versions are envisioned to include yield parameter of the negative binomial distribution.
loss predictions. These changes in the distribution pattern were
most evident in the transplanted rice. Disease
Interfacing Disease Severity to the IBSNAT severity was determined using a pictorial key
Ceres Rice Model: A Computer Simulation of (with 0-8 rating) of increasing severity. Inci-
dence of each severity level was found to
Rice Yield Loss. S.B. Calvero, Jr. and P.S. dence of each severity
Teng. IRRI change with time. The incidence-severity
Teng. IRRI relationship was determined to be a function
of epidemic rate as affected by the vector
Simulation of blast effects on yield was population and the rate of growth of the host
done using the IBSNAT (International Bench- populant. GLH population increased notably
mark Sites Network for Agrotechnology) during the vegetative stage of the crop and
Ceres-Rice model by incorporating different remained high until 75 days after transplanting
disease severities with the potential leaf area and days after seeding.
calculated by the model. Two approaches were
used in the model to determine its ability to
estimate yield loss after incorporation. Firstly, Rice Disease Survey in Bulacan, Pampanga,
one severity level at a time throughout the and Nueva Ecija. F.A. Elazegui, A.J.P. Mag-
emergence and juvenile stages of the crop were naye, G.B. Jonson, P.S. Teng and H. Hibino.
interfaced. Secondly, severity values of 5%, IRRI
50%, and 45% at emergence, juvenile, and floral
initiation stages of rice, respectively, were used.
With the different isoloss curves produced from A disease survey was conducted on 90 rice
the simulation runs of the model, it was observ- farmer's field in three provinces during the
ed that by interfacing severities with leaf area, 1987-88 wet season, as part of the IRRI Inte-
simulated biomass (leaf, stem, root, and panicle grated Pest Survey. In each field of about one
weights) and yield were reduced as compared hectare, a zigzag sampling pattern was used,
with no disease severity. However, simulated with 12 hills/field. Fields were visited at 30-
tiller number showed increasing values with in- day intervals starting from 21-day old seedlings.
creasing severity. This discrepancy in tiller Besides disease data, growth stage and general
values will determine further studies and devel- stand of the crop, water status, inputs applied,
opment of the rice model. and grain yield were also recorded. Data were
summarized using RBASE System V on an
IBM-PC AT computer. Sheath blight was the
most prevalent disease, followed by narrow
,Epidemiology of Rice Tungro in Transplanted brown spot, stem rot, sheath rot, and bacterial
and Direct-seeded Rice. E.R. Ferrer, N.G. leaf streak. Tungro was not observed in the
Fabellar and P.S. Teng. IRRI field and only very minimally detected in the
laboratory using serology. Hirschmaniella sp.
An epidemic of the rice tungro during the was observed in most fields but the population
dry season, 1987, was quantified through a was low. There was no serious disease during
disease progress curve, spatial distribution this cropping season. Spraying against disease
pattern and incidence-severity relationship. A was not a common practice among the
susceptible rice cultivar IR42 and two planting farmers. Most fields in Bulacan and Nueva Ecija
methods, namely transplanting and direct- were planted to IR42 and IR64, respectively.
seeding were used. The green leafhopper The average yield was 4.6 t/ha; low yields were
(GLH), Nephotettix virescens, population was mainly due to drought.






Jan. & June 1988 Abstracts of Papers


Wilt Reaction of Pigeonpea (Cajanus cajan)
Genotypes at SMARC-USM, Kabacan, N.
Cotabato. Naomi G. Tangonan and T.B. Baya-
ron. USM

Forty-six pigeonpea genotypes were screen-
ed for wilt reaction at SMARC-USM, Kabacan,
Cotabato, as part of the 6th International
Pigeonpea Wilt Nursery (IPWN).
Standard cultural practices were followed.
The area used (known to be a "sick plot")
was plowed once and harrowed twice. No
inoculation was done as natural infection was
relied upon. Each genotype was planted in a
5-meter row spaced at 75 cm between hills with
one plant per hill. The set-up was replicated
two times. Wilt ratings were taken weekly until
the plants were about two months old.
Percentage infection of wilt in pigeonpea
ranged from 0 to 9.61. The wilt-susceptible
check (ICP 2376) sustained a mean percentage
infection of 6.53. Twenty genotypes showing
no wilting reaction were classified as resistant.
The other 25 pigeonpea genotypes showed
varied wilting reactions.


Disease Incidence in Seven Jute Accessions al
SMARC-USM, Kabacan, Cotabato. N.G. Tango-
nan and P. Sanico. USM

Four diseases were observed on seven jute
(Corchorus olitorius) accessions planted in
August 1987 at SMARC-USM, Kabacan, Cota-
nato.
Macrophomina phaseoli causing stem and
root rot infected all seven accessions with
percent infection ranging from 1.03 to 1.76;
leafspots caused by Colletotrichum corchori
and Cercospora corchorica likewise infected all
jute accessions with 1.61 to 2.59% infection,
pod molds caused by Macrophomina phaseoli
had percentage infections that ranged from
52.60 to 59.73; while root galls caused by a
species of nematode had severity ratings of
0.71 to 1.65.
In all instances, no significant differences
were noted in the percentage and severity in-
fection of these diseases. Furthermore, the


effect of diseases on the agronomic characters
like days of flowering (20), plant height (119.6
to 228.7 cm), and dry fiber yield (131.16 to
179.20 kg/5 meter row) were not significantly
different from each other.


Survey and Control of Potato Cyst Nematode,
Globodera spp., in the Highlands of Northern
Luzon. T.A. Khayad and E. Ferrer. BPI

A five year nematological survey on the
incidence of potato cyst nematode (PNC) in
the potato production areas of Atok, Maday-
men, Natubleng, Sinipsip, Pactil, Cada, located
in Benguet and Mountain Province was
conducted in 748 farms. Only 49 fields have
infestations with counts of cyst per 100 grams
soil ranging from 1 to 312, an average of 300
egg/larva per cyst.

Results also indicate that harvesting of
potato tubers 70 to 80 days after planting
reduced PCN population densities. In addition,
the reproduction rate of the nematode decreas-
ed to about 30% after a four year crop season
by planting susceptible and resistant potato
varieties alternated with non-host crops such as
cabbage, sweet peas, and carrots.


Survey and Identification of Major Diseases
Affecting Fruit Crops in the Highlands of
Northern Luzon. E.A. Verzola and J. Mangal-
tag. BPI

The areas coveredin this study were Benguet,
Mt. Province and Baguio City which partly
constitute the Cordillera Region of North
Luzon. Expansion in the production of semi-
temperate fruit crops successfully growing in
some areas will greatly depend on pest manage-
ment strategies since these crops are not
exempt from disease attacks. Survey and identi-
fication of such diseases will form the basis of
developing a suitable and effective pest manage-
ment program.
Preliminary results of the study are present-
ed in this report.


List of reviewers of vols 23 & 24
Dr. Delfi B. Lapis, Dr. Rodrigo B. Valdez, Dr. Teresita M. Espino, Dr. Virginia Cuevas, Dr.
Tiburcio T. Reyes, Dr. Samuel C. Dalmacio, Dr. Asuncion K. Raymundo, Dr. Tricita H. Quimio,
and Dr. Marina P. Natural.


Jan. & June 1988


Abstracts of Papers









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