Group Title: Journal of Tropical Plant Pathology
Title: Journal of tropical plant pathology
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Permanent Link: http://ufdc.ufl.edu/UF00090520/00014
 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 1971
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: VID00014
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

Full Text



LkY AMn llIINF 107 D


PHILI PINE

PHYTOPA0Pi

CONTENTS
tracts of Paper Accepted for Presidentation at the Eighth Annual
Meeting of the Philippine Phytopathological Society, Zamboanga
City, 3-5 May 1971 ...........1........................ 1

le Nature of Peanut Resistance to Meloidogyne hapla
SM.B. Castillo, C.C.- Rusell and L.S. Morrison ................ 15
eliminary Study of the Transmission of Philippine Tomato Leaf Curl
Virus by Bemisia Tabaci ... M.L. Retuerma G.O. Pableo and
W.C. Price .... ................ ...... ................. 29

usessment of Yield Loss due to Bactereal Leaf Streak of Rice
O.S. Opina & O.R. Exconde ............................. 35

ant Parasitic Nematodes in Corn-Growing Areas: II. Luzon & Visayas
JJ. Walawala and C.P. Madamba .......................... 40

ithogenicity and Toxicity of Cryptomela acutispora on Black Hulles
Barley
A.C' Pizarro and D.C. Amy .................... ......... 44

semical Control of Downy Mildew of Corn:
1. The Use of Protectant- Fungicides
S.C. Dalmacio and O.R. Exconde ......................... 53
PHYTOPATHOLOGICAL NOTE
uniformm Nematode, Rotylenchulus sp., in Mungo, Soybean and Pea-
nbt Soils at.the UPCA Central Experiment Station
M.Bi Castillo ........................................ 61
: Official Organ of
THE PHILIPPINE PHYTOPATHOLOGICAL SOCIETY
tered as second icasm mail matter at the Manila Post Office on 22 September 1970.


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Ltd., 29QQ Faraday St. corner puth Expressway, Fjzl





















PHILIPPINE PHYTOPATHOLOGY
Official Organ of the Philippine Phytopathological Society


EDITORIAL BOARD

A. N. PORDESIMO, Editor-in-Chief, Department of Plant Pathology
University of the Philippines, College, Laguna
C. A. CALICA, Bureau of Plant Industry, San Andres, Manila
B. P. GABRIEL, University of the Philippines, College, Laguna
M. E. LOPEZ, Philippine Sugar Institute, Quezon City
A. L. MARTINEZ, Bureau of Plant Industry, Lipa City
DOLORES RAMIREZ, University of the Philippines, College, Laguna


BUSINESS MANAGEMENT

Subscriptions: Communications should be addressed to the Treasurer, P.P.S. c/o De
apartment of Plant Pathology, UPCA, College, Laguna E-109. Philippine Phytopatholog.
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be a


ie of contributions of exceptional merit. It may also invite distinguished
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Reprints: Reprints of articles may be ordered upon author's consent to
.,U- IM1


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ABSTRACTS OF PAPERS ACCEPTED FOR PRESENTATION
AT THE EIGHTH ANNUAL MEETING OF THE
PHILIPPINE PHYTOPATHOLOGICAL SOCIETY
ZAMBOANGA CITY, 3-5 MAY 1971

(Arranged alphabetically according to first author's surname)

Reaction of Oryza nivara and Taichung Native 1 to grassy stunt.-
V. M. Aguiero and K. C. Ling. The reactions of different species c
Oryza, rice varieties and selections to grassy stunt were studied using th
mass screening method of inoculation. From 1968 to 1970, a total c
10,106 entries of these were tested; except one line of Oryza nivara, non
showed consistently lower than 30% infection.
In a comparison test using the mass screening method, 2.6% of th
2, 860 0. nivara seedlings and 88.5% of the 2,663 Taichung Native
seedlings were infected. By varying the method of inoculation, viz
lengthening the inoculation feeding time, varying the insect number pe
test seedling, and using different number of infective insects, 0. nivar
showed consistently low percentage of infected seedlings than Taichunr
Native 1. Infected plants of 0. nivara that showed typical symptoms couh
serve as source of inoculum; about 26.5% of the insects became infectiv
after feeding on such infected plants. The incubation period of the grassy
stunt pathogen was 8 to 23 (average 11.4) days; the number of disease
transmitting days ranged from 0.14 to 0.69 (average 0.48). Of the viruli
ferous insects confined on 0. nivara, about 28% became infective, and o
those confined on Taichung Native 1, 29.3% became infective, indicating
that 0. nivara did not alter the infectivity of the insects. The percentage
of grassy-stunt infection, regardless of variety, decreased with plant age
when infected. But the degree of decrease varied among varieties. Plant
that became infected at an older age but remained symptomless before
harvest showed the characteristic grassy-stunt symptoms in the regenerate
growth. Results of recovery test revealed that these symptomless plant:
could serve as inoculum source and that the percentage of infective in
sects is low.
Transmission of tungro by nymphs of Nephotettix impicticeps. -
M. P. Carbonell and K. C. Ling.- The ability of N. impicticeps nymph,
at different instars to transmit tungro was studied. The nymphs were
first fed on diseased leaves for 24 hr and then transferred to young and
healthy Taichung Native 1 seedlings where they were allowed to remain
until they molted. A reacquisition feeding on the inoculum source was
given to the nymphs immediately after each molting.

1









PHILIPPINE PHYTOPATHOLOGY [VOL. 7

All the nymphal instars were able to transmit the disease; the highest
cdentage of transmission (68%) and virus retention period (4 days) were
ained with the 5th instar. The percentage transmission (86%) of adult
ects was still higher than that of the nymphs. At different ages of test
nts, the first-instar nymph transmitted the disease even to 40-day-old
dlings. The percentage of infection decreased with the increase in plant
!. Like the adults, the nymphs were strictly phloem feeders. Cross-
tion of a leaf blade showed that 82% of the total feeding tracks of the
it-instar nymphs terminated at the vascular bundle; 73% of these were
ind at the phloem cells indicating that the nymphs preferred this
;ue. The positive transmission of tunero by the first-instar nymphs











UU~fr/* .,U UL -.v Si J^al" Ji t. W V .a-JA II1'.ALrtt. Va t VV at alim. a L FAA
2.5, 3, and 11. The number of pycnidia and pycnidiospores produced at
a pH range of 4 to 10 follows a normal distribution curve.
Bacterial stripe of corn.- Asuncion D. Karganilla, O. R. Exconde, and
E. Q. Funtanilla. Bacterial stripe is a common disease in corn fields.
In either young or mature plants, it occurs as oil-soaked, translucent
lesions and starts in the form of spots. Physiological tests revealed that the
causal bacterium is Pseudomonas albopricipitans. This bacterium infected
wheat, oat, rice, sorghum and 4 species of weeds with varying degrees of
severity. Of the 93 test corn entries, 8 were rated highly resistant, 39
were resistant, 38 were intermediate, and 8 were susceptible to bacterial
stripe during the dry and wet seasons.
A medium for single-colony growth of Xanthomonas oryzae.--Asuncion
D. Karganilla, S. H. Ou, and Marina Paris. -Wakimoto's medium was mo-
dified for single bacterial colony development. The addition of 0.05%
FeSO4 enhanced single-colony growth. The removal of potato resulted in
the development of bigger colonies. In comparable tests, Silva's, Goto's,
and Suwa's media induced the production of single colony but Tanaka's,
Watanabe's, NIAS's, and Kado's media did not. The modified Wakimoto's
medium gave the highest number of single colonies recovered by surface
plating. Furthermore, it was found to be a suitable medium for the isola-
tion of X. oryzae from infected leaves.
A solution-feeding method for Nephotettix impicticeps.- K. C. Ling.-
A method was developed for testing the effect of chemicals on the life
span of adult N. impicticeps as well as the infectivity of tungro-viruliferous
insects. The method consists of putting about 1.5 ml of solution on the
outside of the base of an inverted 400-ml beaker and then stretching a piece
of Parafilm over the base. A plastic cover, 5.5 cm diam and 1.5 cm high
with openings for ventilation and entrance of insect, is placed over the
membrane. With an aspirator, as many as 40 insects are placed on the
membrane under the cover. The solution and the membrane are changed
every morning, and the dead insects are counted. The following evidence
suggests that the insects can feed on the solution through the membrane:
1) minute pores were apparent on the membrane after the insects had
been confined on it; 2) insertion of insect stylet through the membrane
was observed under a stereoscopic microscope; 3) life span of insect was
longer when fed on sugar solution than on solution without sugar or
water only; 4) insects died early if the solution contained an insecticide or
toxic substance; and 5) incorporation of amino acid from the solution in
the proteins of insect was proven by radioactive tracing technique. N. im-
bhirticrphc when fprl nn tloranr cnhltinnr /(1 9r tn Ino%\ hV1A ., ;f- rn








lLLIrriiNL rI-iI IL~ArftV~IIrLJ.


tons generally increased tne Ite span ot tne insect. A pi- lower tan
4.0 or higher than 8.5 shortened the life span of the insect. When the
concentration of histidine monohydrochloride was 0.2 mg/ml or higher, the
life span of the tungro-viruliferous insect was significantly shorter. At
concentrations of lower than 0.5 mg/ml, alanine, asparagin, and aspartic
acid had no marked effect on the life span of viruliferous N. impicticeps.
In testing the effect of chemicals on the infectivity of the insect, viruliferous
insects were usually confined on the feeding solution for 6 hr and then
transferred individually to the test seedlings for infection feeding of 16
hr. The infectivity of the insect was demonstrated in the infected seed-
lings; the percentage of infected seedlings reflected the effect of chemicals
on insect infectivity. This method can also be used for Nilaparvata lugens.
Loss of tungro infectivity by Nephotettix impicticeps after molting.-
K. C. Ling and M. P. Carbonell.- During molting, a new epidermis forms
under the old skin. Then the old skin ruptures allowing the insect to
emerge. The cleft forms along the dorsal median line of the head and
thorax. When exuviae is shed, the general cuticle enclosing the body and
appendages and the linings of most of the tracheal tubes and the stomodaeal
and proctodaeal parts of the almentary canal are lost. A microscopic
examination of the exuviae of N. impicticeps revealed that the mouth por-
tion consists of the external structure of labium, labrum, and stylets, in-
cluding both mandibles and maxillae. Consequently, the old stylets are cast
off when the insect molts. An examination of the insect's stylets at early
molting stage revealed that the new stylets are inside the old ones. When
an insect feeds on a diseased plant, the stylets and alimentary canal un-
doubtedly are contaminated with the virus. If the virus particles are dis-
tributed only on the surface of the stylets and the lining of the alimentary
canal without penetrating into tissues under the epidermal layer, then the
virus particles must be cast off with the exuviae during molting, thus
freeing the insect of the virus. An insect that has no virus cannot be
infective. This may explain why infectivity is lost after molting; upon
exposure to diseased plant, however, a molted insect is still able to transmit
the disease.
Effect of pH on the transmission of rice tungro virus by viruliferous
Nephotettix impicticeps.- K. C. Ling, M. P. Carbonell, and D. Dima-
suay. After acquiring the rice-tungro virus from infected plants, N. impic-
ticeps was allowed to feed for 6 hr on a solution (solution feeding method)
with varying pH ranging from 4 to 10 at intervals of 0.5. The infectivity
of the insects, measured by counting infected seedlings, was not substantially
affected, regardless of the growth stage of the insect or the pH of the solu-
tion with or without buffer. Below pH 4, however, the number of in-
fective insects decreased. This was confirmed by testing more than 3,500
viruliferous insects on 4 buffer solutions (aconitate, citrate, citrate-phos-
phate, and phthalate-HC1) at a concentration of 0.02 M. The percentage


V mv Q I








ABSTRACTS


of infective insects obtained after feeding on solutions of varying pH was
43.4% at pH 4.2, 38.9% at pH 4, 25.7% at pH 3.8, 13.3% at pH 3.6,
5.2% at pH 3.4, 4.0% at pH 3.2, 2.7% at pH 3, and 1.2% at pH 2.8.
The number of infective insects dropped as the pH decreased. The pre-
sence of feeding punctures on leaves exposed to the insects which previous-
ly fed on the solution with pH 3 convincingly showed that the decrease in
the number of infective insects is not due to the inability of the insect to
feed on rice seedlings. Furthermore, the life spans of the insects feeding
on rice seedlings after they had fed for 6 hr on solutions at pH 3, 4, and
6 were similar. Hence, the failure of the virus to persist in the insect
indicates that low pH inactivates the virus.
Distribution, translocation and spread of the greening pathogen in citrus
trees. A. L. Martinez. The greening pathogen was found to be unevenly
distributed in affected citrus trees. Some of the growing scions of the
propagations by budding from severely yellowed and mottled twigs of in-
fected trees developed greening symptoms; the others appeared healthy.
Isolation of the greening pathogen from such healthy-appearing scions con-
sistently yielded negative results. Additionally, direct inoculations from
healthy-appearing twigs of diseased trees to citrus seedlings induced no
greening symptoms.
The greening pathogen was experimentally demonstrated to be trans.
located in the phloem and not the xylem. It failed to move either up-
ward or downward through the girdled portion of the stem of citrus seed-
lings. It was also experimentally demonstrated that the greening pathogen
can move from the inoculum buds to the citrus seedling stocks in 7 days.
It appeared to spread slowly in an orchard tree. When introduced into
a healthy branch by tissue grafting, it remained rather confined to that
branch without invading the whole tree. Possibly the quick spread of the
greening pathogen in old trees is dependent on the external spread by its
introduction by multiple feedings of infective Diaphorina citri Kuway,
its principal psyllid vector and not so much on internal movement.
Effects of tetracycline antibiotics on citrus greening pathogen. -
A. L. Martinez, D. M. Nora, and A. L. Armedilla. Achromycin (tetra-
cycline HC1), Tetrachel (tetracycline HC1), Terramycin oxytetracyclinee
HC1), and a pure form of tetracycline were demonstrated experimentally
to have inactivating effects on the citrus greening pathogen. The test
seedlings of various citrus cultivars that were bud-inoculated from greening-
infected budsticks previously immersed in a 1000 ppm solution of each
tetracycline compound for 25-30 min developed no greening symptoms with-
in 4-10 months of inoculation. In contrast, all the test seedlings that were-
inoculated with non-treated infected buds developed typical symptoms with-
in 45-75 days. At a concentration of 100 ppm, Achromycin and Terramy-
cin applied as foliar spray to seedlings and budlings with severe greening'


Nos. I &c 2]









PHILIPPINE PHYTOPATHOLOG


symptoms, induced development of more chlorophyll and production c
symptomless side and terminal shoots. When these sprayed plants wer
used as inoculum sources, only 25% of the inoculated test seedlings show
greening symptoms; the others did not. But when the source of inoculur
was non-sprayed infected plants, 100% of the test seedlings develop
greening symptoms. In comparable tests, Achromycin, Tetrachel, and Tei
ramycin had no effects on the viruses of tristeza and seedling-yellow!
The results of these studies strongly indicate that the tetracycline ant
biotics applied by immersing infected budsticks in a solution ina4
tivated completely the greening pathogen in the budsticks, but the sam
antibiotics applied by spraying infected plants inactivated partially th
greening pathogen contained in them. The results herein presented fmu
their support our earlier contention that the etiologic agent of citru
greening disease in the Philippines is a mycoplasma-like organism rathe
than a virus. Final proof of the mycoplasma-like agent of this citru
disease rests on the completion of the rules of proof of pathogenicity.
Inheritance of resistance to grassy stunt.- F. L. Nuque, V. M. Aguiers
and S. H. Ou.- A strain of Oryza nivara resistant to grassy stunt wa
crossed with 4 varieties and new breeding lines, viz., IR8, IR20, IR661
and IR773 in 6 combinations. The F1, F&, backcross 1, and backcross 2 a
well as the parents were inoculated at seedling stage. The FI plant


and 2 show
the theory
to grassy
rnes.


inherited and
stence of Xar
and S. H. Ou.
which increases


death of JC-70 leaves, regular observation by reisolation and plating oi
streptomycin-treated Wakimoto agar was made on the bacterial population
resulting from 4 sections of the lesion: 1) inoculation point, 2) 1 cm fror
inoculation point, 3) mid-portion of the lesion, and 4) advancing tip of th
lesion.
T'tr, .....l1. f,'r'\nrtrA -tht *th hl;rhPQt hnrtPril nAnnil2tion ia a]


[VOL.












he average bacterial population on these 2 portions were 292, 5; 908, 30;
.66, 0; and 313, 0 at 4 stages of lesion development, respectively. The
populationn dipped abruptly in lesions of the susceptible variety than in
hose of the resistant one; 3-week-old lesions contained a very few or no
bacteria It is likely that the organism lives and multiplies mostly in the
giving tissues of the plant and that it does not undergo a long period of
aprogenesis in non-living tissues. The pathogen can establish and multi-
)ly in tissues of the resistant variety just as it does in the susceptible one
although lesion development in the former is very much restricted. That
he size of lesions is reflected by the population of the pathogen seems
likely. The actual mechanism involved in lesion development was not
investigated.
Control of soil rot of untrellised tomato. Faustino P. Obrero. Four
oil fungicides, viz., Captan, Brassicol (PCNB), Benlate, and Soil-Treater
(Captan-PCNB) were tested by blanket application for controlling soil rot
)f untrellised tomatoes caused by Rhizoctonia solani and Sclerotium rolfsii.
The experiments were conducted in artificially-infested soil in the green-
iouse and in a field with a known history of soil rot. Ten pounds PCNB
>er hectare effectively controlled both Sclerotium and Rhizoctonia soil rots of
omato fruit; 5 to 10 lb, active Benlate per hectare was effective only
against the latter. Soil-Treater and Captan reduced incidence of both soil
-ots of fruit but were less effective than PCNB.
Grafting tomatoes to control bacterial wilt. -Faustino P. Obrero. -
Bacterial wilt, caused by Pseudomonas solanacearum EFS, is one of the
serious diseases of tomato. The pathogen occurs in tropical and subtropical
ireas of the world. Once established, it remains there for many years.
infection takes place through the roots; the bacterium multiplies in the
vascular system where it causes a brown discoloration of the woody stem
followed by wilting and rapid collapse of the foliage. Attempts to control
his disease in the field by soil fumigation have been unsuccessful. A
ew resistant tomato lines have presently been developed but their fruit
ize and other agronomic qualities are still inferior. Grafting susceptible
commerciall varieties of tomato to resistant rootstock as a method of con-
rolling bacterial wilt was studied in Hawaii. The University of Ha-
vaii Selection 5808-2 from current tomato Lycopersicon pimpinellifolium
dill. was selected because of its high resistance to bacterial wilt and its
excellent compatibility with all the commercial varieties used as scions. A
apid and reliable grafting technique was developed enabling one to graft
'0 to 100 plants in 1 hr with 95% success.
In field tests, the percentage of bacterial wilt incidence was 3% on
grafted plants and 70% on non-grafted ones. Using a high yielding
lawaiian tomato hybrid (N-52) as scion, the estimated yields were 33.7,













pectively. The rootstock was also found unaffected by any root injury or
root-knot infestation. But the resistant rootstock conferred no resistance to
the scion when the wilt bacterium was introduced above the graft union.


and other plant species. -F. M. Olivares, Jr., Aurelia A. dela Cruz, and
Lagrimas B. Salisi. Studies on the transmission of tobacco leaf-curl virus
by the whitefly (Bemisia tabaci Genn.) to a number of vegetable species
belonging to the families Cruciferae, Solanaceae, Cucurbitaceae and Legumi-
nosae were conducted at the Maligaya Rice Research and Training Center,
B.P.I., Mufioz, Nueva Ecija. Non-viruliferous whiteflies reared on disease-
free batao or hyacinth bean (Dolichos lablab L.) were first fed on infected
tobacco plants for 24 hr and then transferred to healthy test plants for in-
fection feeding of 4 days. Various types of leaf abnormalities were observed
on pechay (Brassica chinensis L.), mustard (B. juncea Goss), radish (Rapha-
nus sativus L.), tomato (Lycopersicon esculentum Mill.), egg-plant (Solanum
melongena L.), sweet pepper (Capsicum annuum L.), squash (Cucurbita
maxima Duch.), sitao (Vigna sinensis var. sesquipedalis Frunv.), cowpea
(V. sinensis), and Asystisia coromandeliana after infection feeding by the
whiteflies. These abnormalities appeared within 10 to 20 days after inocu-
lation. Recovery tests have not yet been completed. Cabbage (B. oleracea
var. capitata L.), cauliflower (B. oleracea var. botrytis L.), potato (S. tubero-
sum T.\ amnalava IMomordirc rharnntin T.1 and nra Irr AhPlmncrh n c.








ABstRAcTs


s. Although most of these races were non-pathogenic to Tetep, all of
i were pathogenic to KTH. Of the 450 single-conidial subcultures, 320
Snon-pathogenic to Tetep and 447 were pathogenic to KTH. The
age number of lessons produced was 1.6 on Tetep and 37.4 on KTH.
i study demonstrates that Tetep maintains its resistance to blast despite
occurrence of new pathogenic races.
Chemical control of rice blast. S. H. 'Ou, F. L. Nuque, T. T. Ebron
J. M. Bandong, and O. Garcia. Three new systemic fungicides, viz.,
55, NF-44, and NF-48 were found as effective as Benlate in warding off
t infection. Soil treatment experiments showed that NF-35, NF-44, NF-48,
Kitazin effectively controlled leaf blast under nursery condition of
y inoculum. NF-35 and NF-44 had a high residual activity in the soil;
sted for more than 4 months. Granular Kitazin applied at the rates of
60, and 120 kg/hectare effectively controlled neck blast and appreciably
eased yield even under field conditions of severe blast incidence. In
-treatment experiments conducted in the blast nursery, Benlate, NF-35,
NF-44 effectively reduced the number of leaf blast on the seedlings.
results obtained in farmer's field showed that spray application of Hino-
NF-35, NF-44, Kitazin, and Benlate can control neck blast. During
re neck-rot incidence, the treated plots yielded significantly better than
control. From an economical point of view, Benlate, NF-35, NF-44, Hino-
and Kitazin as foliar-spray materials and granular Kitazin as soil-treat-
t fungicide may be applied in farmer's field with severe blast incidence
ave the crop from a heavy loss.
Chemical control of bacterial blight of rice. S. H. Ou, F. L. Nuque,
I. Agrawal, S. Merca, and O. Garcia. TF-130, a new systemic bactericide,
tested to control bacterial blight of rice. Preliminary results showed
0.01 to 0.08 g of TF-130 applied to a 6-inch pot of soil at 1 and 5
before and after inoculation satisfactorily controlled bacterial blight.
:n used as seed treatment material, it was not effective.
The effect of TF-130 was more pronounced by dipping seedlings in a
ppm suspension for longer period prior to inoculation. When sprayed
leaves of seedlings and flagleaves of maturing plants, its effect was less
:tive but at higher concentrations, it still gave a fairly good control.
ower concentrations, its effectivity seemed to be lost 2 weeks after spray
ication suggesting that more than one application is needed to control
erial blight effectively. Further studies are being undertaken to deter-
: the effect of TF-130 as foliar spray and soil-treatment chemical on. the
rol of bacterial blight under field conditions.
Preliminary study on transmission of Philippine tomato leaf-curl virus by
isia tabaci. M. L. Retuerma, G. O. Pableo, and W. C. Price. A
ise of tomato (Lycopersicon esculentum Mill.), referred to here as Phil-
ne tomato leaf curl (PTLC), has been a serious problem in Albay Pro-


1 & 2]









PHILIPPINE PHYTOPATHOLOGY


fince since 1968. We found the disease to be caused by a virus or vin
pathogen which is transmitted by the whitefly (Bemisia tabaci Genn.:
by grafting but not by mechanical methods. The pathogen failed to
Nicotiana tabacum L., N. glutinosa L., and Datura sp. which are knoi
be susceptible to tomato yellow leaf-curl virus (TYLCV) occurring in ]
and to tobacco leaf-curl virus (TYLCV) occurring in the Philip
Therefore, PTLCV is not identical with either TLCV or TYLCV ald
it may be related to them. B. tabaci was found to transmit PTLCV
an acquisition feeding period of 1 hr or shorter and an infection
ing period of 3 min or shorter. A minimum of 2 whiteflies transn
the virus after suitable acquisition and infection feeding periods. The
mum level of transmission was obtained with 10-20 whiteflies.
Variation in adaptability of Nephotettix impicticeps to rice
rieties. -C. T. Rivera and K. C. Ling. -The rice green leafhopper
impicticeps) from IRRI colony was tested for its ability to adapt or
petuate on seedlings of Pankhari 203, a variety resistant to this leafhi
and to tungro. By rearing continuously on Pankhari 203 over several g(
tinnc a. rnoP nf tho olafhnnnPr Irlpiernatorl P9(4 rnlnnva\ whirh rnenrlr


most of the other varieties tested. Nephotetttx impicticeps was more


10









1


~___


ve but a combination of surface and in-furrow dust application pro-
good control 2 weeks after planting. Chloroneb alone was promis-
vhen the soil surface was drenched with 3 fungicides (chloroneb,
i, and thiabendazole). Incorporation of chloroneb granules prior to
ng was effective for 2 weeks after emergence but failed to provide
led control thereafter. Foliar application tests involved the evalua-
Af chloroneb by foliar spraying, foliar dusting, whorl application of
les and dry wettable powder, and introduction of chloroneb-coated
ernels and mungo seeds into whorls. Foliar application was combined
several seed and soil treatments as well as with overnight covering
ants with rice straw or banana leafsheaths immediately after emer-
Most effective were combination treatments involving seed treat-
plant covering and foliar spraying. The application of chloroneb-
I seeds and granules into the whorls in combination with seed treat-
and plant covering also showed promise. In the non-fungicidal cate-
soil application of the systemic insecticides Temik and Furadan and
spraying with phenyl mercuric acetate did not affect disease reaction.
addition of Deep Penetrant to chloroneb sprays improved control but
and dimethyl sulphoxide failed to do so. Dimethyl sulphoxide and
Penetrant applied to seed in combination with chloroneb did not sa-









PHILIPPINE PHYTOPATHOLOGY


Predicting the occurrence and development of powdery mildew of mun-
go. J. A. Soria and F. C. Quebral. The occurrence and development of
powdery mildew of mungo at UPCA. Central Experiment Station are
highly correlated with the concentration of airborne conidia, age of sus-
cept, and prevailing environmental conditions such as temperature, relative
humidity, wind speed, solar radiation, and rainfall.

Hourly concentrations of airborne conidia were higher during noon-
time than in the afternoon. Conidial density was highest in January when
the average temperature, relative humidity, wind speed, total solar radia-
tion, and rainfall was 25.6 C, 85%, 1.8 mph, 9976 g cal-cm2-day, and 1.6
inches, respectively. Under these conditions, the experimental plants be-
came severely infected 26 days after planting and the disease rating was
98.33%.

Spore germination tests on detached mungo leaves showed that conidia
introduced in early morning and midnoon germinated best at 85.5% relative
humidity and those introduced in late afternoon germinated best at 80%
relative humidity. A tentative schedule for predicting the occurrence of
powdery mildew has been based primarily on disease appearance, suscept
age, and meteorological factors.
Phenolic compounds in relation to rice blast. R. S. Sridhar and S. H.
Ou. A correlation between the degree of resistance and phenolic level in
plant tissues has been shown in many studies on host-parasite relationship.
A higher level of phenolic compounds in the diseased tissues has also been
noted in many physiopathological conditions. Rice is known to contain
several polyphenols. The toxicity of different phenolic compounds to the
rice blast fungus (Pyricularia oryzae Cav.) was assessed; the toxicity of these
phenolics was found to increase as their concentrations increased. Phenolic
compounds upon oxidation became highly reactive and toxic to the pathogen.
The oxidation process was apparently mediated in rice plants by peroxidase
enzyme system because polyphenol oxidase is absent in rice plants. When the
spores of P. oryzae were germinated in a, medium containing phenolic com-
pounds, they turned brown suggesting that the pathogen has the ability to
produce oxidase. Moreover, a significant increase in peroxidase activity was
noted in the inoculated susceptible variety from the fourth day onward which
corresponds to the period when a lesion starts to delimit itself. The brown-
ing of the lesion was attributed to the incorporation of oxidized phenols in
the melanin pigment. These oxidation processes of phenols are considered
the defense mechanism of rice plant against the blast fungus.
Ascorbic acid and glutathione, when applied in combination with a
phenolic compound, decreased the toxicity due to their ability to reduce
the oxidized form of the phenolics. The concentration of phenolic com-
pounds, the ability of pathogen and plant to oxidize them, and the levels


[VOL. 7






































'1-U''., Y L I~I~V"U .lLM JAIUL IVU LU U: ICOIIWIIL.
Studies on the pathogenicity of species of Pratylenchus, Tylenchorhyn-
and Helicotylenchus on corn. -J. J. Walawala and C. P. Madamba.-
greenhouse test, 2 of the 3 nematode species isolated from the UPCA
ral Experiment Station, viz., Pratylenchus coffeae (Zimmermann 1898)
jev and Stekhoven 1941 and Tylenchorhynchus martini Fielding 1956,
)duced and/or caused appreciable damage to the test corn varieties
CA var. 1, UPCA var. 2, and Philippine Hybrid 801). The third
es Helicotylenchus erythrinae neither reproduced in nor caused any ap-
it damage to the plants.
Corn plants inoculated with Pratylenchus coffeae exhibited extensive
as and necrosis in the root systems. UPCA var. 1 was evidently the
suitable host. Philippine Hybrid 801 appeared to be the least suitable.

Neither root necroses nor lesions were observed on the 3 varieties inocu-
with Tylenchorhynchus martini. The roots of inoculated plants, how-
were sparse and shriveled. UPCA var. 2 was most suitable to this
es; its population increased by 97% 60 days after inoculation.
Plant parasitic nematodes in corn-growing areas. II. Luzon and Visa-
- J. J. Walawala and C. P. Madamba. In nematode surveys con-


1S









14


lHIL1PPINE FHYTOPATHOLOGY


parastic nematodes were identitied. Isolated trom soil samples
Pratylenchus, Helicotylenchus, Rotylenchus, Scutellonema, Tylenchorhyru
Xiphinema, Meloidogyne (larvae), Trichodorus, Hoplolaimus, Hemicy
phora, Pratylenchus, Criconemoides, and Aphelenchus. The most cor
and widely distributed were Helicotylenchus and Tylenchorhynchus.
tylenchus, Hoplolaimus, and Scutellonema were not widely distributed
occurred in more than 50% of the total soil samples collected. Pratylen
was encountered only in soil samples collected from Cebu. More nema
genera occurred in Cebu; least number was in Camarines Sur. No gal
on corn roots was observed although larvae of root-knot nematodes
recovered from the soil samples.












THE NATURE OF PEANUT RESISTANCE
TO MELOIDOGYNE HAPLA

M. B. CASTILLO, C. C. RUSELL, AND L. S. MORRIsON
Department of Botany and Plant Pathology, Oklahoma State University, Stillwater,
la. 74074. Present address of senior author: Department of Plant Pathology, Uni-
sity of the Philippines, College, Laguna, Philippines E-109.
Portion of the Ph.D. dissertation of the senior author.
Journal Article No. 2227 of the Agricultural Experiment Station, Oklahoma State
diversity, Stillwater, Okla This project was supported in part by USDA, ARS Co-
rative Agreement 12-14-100-56833 (84).

ABSTRACT
The development of Meloidogyne hapla Chitwood in the resistant Arachis
spp. P-287, P-246, and P-258, and galling of P-246 and P-258 were greater on cut-
tings inoculated at the age of 1I months than on cuttings inoculated at the age of
3 months. Plant age did not affect the nematode development in the susceptible
A. hypogaea L. var. Spantex, and the galling of either Spantex, or P-287.
At 28 C 16-hr day and 20 C night regime, the peanut resistance to
M. hapla consisted of pre-infection and post-infection phases. The pre-infection
phase was evidenced by the reduction in larval penetration of resistant roots
which was found due, at least partly, to the less attractiveness of the re-
sistant roots to the nematodes. Resistance at the root surface was also sug-
gested when only 29.0% of the nematodes that were present on the side of
the pot containing a resistant plant were inside the roots. This compared to
88.1% penetration of susceptible roots 7 days after an inoculum was placed
between the resistant and susceptible plants. The post-infection phase was
evidenced by delayed gall formation, decline of nematode population after
40 days, little nematode reproduction, and failure of nematodes to complete
their life cycle within 60 days.
On a per infection basis, no basic differences were detected in the galls
and giant cells of infected resistant and susceptible roots 30 days after inocu-
lation.


Tyler (1941) defined resistance as the ability of the plant to obstruct
natode invasion. Barrons (1939), however, found that, in the 24 resistant
nts that he worked, resistance was manifested by the failure of larvae to
vive after entering. Sasser (1954) reported different types of interaction be-
!en Meloidogyne spp. and various resistant plants, including failure of
vae to enter the roots, invasion by few larvae with no development, and
asion by many larvae with only few developing. Christie (1949) sug-
ted that some plants are easily invaded by larvae while others are not
I that all resistant plants are not necessarily resistant for the same reason.
ler (1941) proposed that resistance may depend, to some extent, on plant

15









PHILIPPINE PHYTOPATHOLOGY


vigor which is dependent on climate, plant nutrition, and other envirc
mental conditions.
Resistance to root-knot nematode penetration has been attributed to I
pulsion or lack of attractiveness of plant roots, toxic plant chemicals, ai
root cell walls that are either too thick to be penetrated or chemically i
sistant to nematode enzymes (Chitwood and Oteifa, 1952; Rhode, 1960).
Resistance, after root-knot nematode invasion, was attributed by Christ
(1936) to the failure of resistant hosts to respond favorably to the stimul
of infection and, therefore, giant cells that serve as food for the nematod
are not formed. Barrons (1939) suggested that resistance may be due
certain chemicals found in the resistant plants that counteract or neutrali
the giant cell-inducing effect of the nematode secretions. Malo (1965) o
served that in the peach rootstocks that were resistant to Meloidogyi
javanica (Treub) Chitwood, the cessation of nematode development ar
the death of nematodes in advanced stage of infection were due to tl
replacement of the giant cells with suberin-like materials and not to
failure of giant cell formation. Hypersensitive tissue reaction was four
associated with resistance to root-knot nematodes in soybean, cotton, tomat
and sweet potato (Dropkin and Nelson, 1960; Brodie, Brinkerhoff an
Struble, 1960; Dean and Struble, 1953; Riggs and Winstead, 1959; Dea
and Struble, 1953).

The present investigation was conducted to determine the nature (
peanut (Arachis spp.) resistance to M. hapla Chitwood.

MATERIALS AND METHODS
The unidentified wild Arachis spp. and a cultivated Arachis hypogae
L. var. Spantex which were previously found to be resistant and susceptible
respectively, to M. hapla were used as test plants in this study. A M. hapi
isolate which was recovered from peanut roots and maintained on tomat
(Lycopersicon esculentum Merr. var. Rutgers) in the greenhouse was use
as inoculum. Plants were infected by either pouring aliquot suspensions cor
training known numbers of newly hatched larvae on exposed roots, placing
pieces of infected tomato roots containing counted egg masses on or around
the exposed roots or mixing with the soil chopped tomato roots which hal
been infected for two months. All experiments were conducted in a controlled
environment chamber maintained at 28 C 16-hr day (light intensity of abou
3500 ft-C) and 20 C night regime. Severity of root galling was rated on a
to 5 scale (1, none; 2, trace; 3, moderate; 4, severe; 5, very severe). To d(
termine the presence of nematodes in infected plants, the roots were stained
with acid fuchsin (McBeth, Taylor, and Smith, 1941). Pieces of stained root
were crushed between two glass slides; nematode development was studied wit]
the use of a microscope. The nematodes were placed in six development


16

































inoci
d fo:


Ten egg masses were randomly hand-picked from the
plant and as many as could be found were hand,
of Arachis sp. P-246. Each egg mass was transferred
a drop of lactophenol, teased apart and then egg 4
the aid of a microscope.
Histopathology of nematode infection in resistai
nuts. --Four 2 1/2-month old cuttings each of Arac.
and Spantex (susceptible) were inoculated singly wil
inoculated plants were washed, transplanted into st
a controlled environment chamber 5 days after in
after inoculation 25 days after transplanting- sam]
about 10 mm long were dehydrated with series oj
alcohol and infiltrated with paraffin. Longitudinal












ble peanuts were compared.
Attractiveness of resistant and susceptible peanut roots to M. hapla. -
An experiment was designed to determine the attraction of M. hapla te
the roots of resistant and susceptible peanuts. One 3-month old cutting
each 6f Arachis sp. P-246 (R = resistant) and Spantex (S = susceptible)
was grown in each half of a splitted 15-cm pot with sterile soil, anc
their roots were separated by a plastic envelope containing 100 cc o
sterile soil (R/S). The pot halves were held together by means of rubber
bands (5-mm), then placed on a 20-cm plastic saucer (Fig. 1A) and kepi
in a controlled environment chamber. The other treatments were R/m
plant (R/NP), S/no plant (S/NP), and no plant/no plant (NP/NP
(Fig. 1C). The pots were watered by filling the saucer. This prevented
the loss of any root diffusates by leaching. After seven days, the plastic
envelope between the pot halves was replaced by a folded piece of tulli
containing 2 g of chopped infected tomato roots thoroughly mixed ii
100 cc of sterile soil. In order to obtain an even thickness of the in
fested soil in the tulle, replacement was accomplished by first laying th<
tulle on a level glass on top of one of the pot halves (Fig. 1B) and late
the glass was carefully removed leaving the tulle behind. The pot halve
were rejoined by -rubbr bands as in the above technique. After sever










B








Fig. 1. Split plot design used to determine Meloidogyne hapla attraction to pean
roots. A) Soil-filled plastic spacer envelope between resistant and susceptible peasnau
B) Pot halves showing pass plate, tulle envelope containing nematode-infested soil, am
plant position at inoculation; C) Treatments from left to right. R/S, R/no plan
S/no plant, and no plant/no plant.







































f-24?W Y.t Z.Z 32.U zM.i 10.1 0a.t
P-258 3.2 2.3 66.2 28.9 54.2 32.3
a Lines indicate no significant difference at P = 0.05 with analysis of varience
technique; values are averages of 12 readings.

old plants. Significantly higher percentages of nematodes r ached adult-
hood in the young than in the old plants of the resistant iArachis spp.
P-237, P-246, and P-258, but not of the susceptible control.
Nematode penetration and development in young resistant dnd suscep-
tible peanuts. -Table 2 shows the differences in nematode penetration
and development and time of galling in young resistant and .susceptible
peanuts. Galling occurred within 2-4 days in the susceptible Spantex
and 5-10 days in the resistant Arachis sp. P-246. The highest recovery,
after 30 days, of the first generation nematodes from the resistant peanut
was 61% of the original inoculum, compared to 98% from tle -susceptible
peanut. None of the nematodes in group D and E were recovered after
20 days and 30 days, respectively, from the resistant peanut; nematodes
in group D and E were recovered after 20 days and 30 days, respectively,
from the susceptible peanut. An examination of nematodes in the soil as
well as the nematode counts in the roots did not indicate any completion
of a nematode life cycle in the resistant peanut after 50 4ays. Second


-t-n














TABLE 2. Nematode penetration and development in young resis

Days after Archis sp. P-246 (Resistant)
Inoulatioa A B C M D E Total A


1 4.0 4.0 6.0

2b 5.7 5.7 11,2

3 9.0 9.0 25.0

4e 11.2 11.2 62.7

5 21.0 21.0 120.2

10d 67.5 2.7 70.2 177.5

20 309.0 262.0 22.7 0.5 594.2 509.0

30 58.5 899.7 90.7 2.5 62.5 618.9 39.5

40 22.5 120.5 81.0 51.0 127.0 0.7 402.5 108.2

50 11.7 52.5 49.7 33.2 133.2 5.0 285.8 187.7
Each plant was inoculated with 1000 larvae; values are averages of counts
b Root tips of 2 plants of A. hypogaea 'Spantex' were galled.
eRoots of all 4 plants of A. hypogaea 'Spantex' were galled.
SRoots of all 4 plants of Arachis sp. P-246 were galled.


.,. .=. ,.


: : ~








LASTILLO, ET AL.: PEANUT REI


in the susceptible. Most of the egg masses that were found in the re-
sistant peanut were empty and that the average number of eggs per egg
mass was only 0.7, compared to 222.9 in the susceptible. Second gene-
ration larvae were found in the roots of the susceptible peanut, but none
in the roots of the resistant.
Histopathology of nematode infection in resistant and susceptible pea-
iuts. Nematode infections were accompanied by gall and giant cell for-
nations, not only in the roots of the susceptible Spantex, but also in the
-oots of the resistant Arachis sp. P-246. However, the galls were relatively
smaller in the resistant than in the susceptible peanut. Fewer infections
mnd less developed nematodes were observed in the resistant than in the
u-.ceptib!e peanut. On a per infection basis, no basic differences between
he anotomy of infected roots of the resistant and the susceptible peanuts
vere detected. The size and number of giant cells formed by one nema-
ode were nearly identical, regardless of the resistance or susceptibility of
est plants (Fig. 2). Giant cells in the resistant roots usually caused as
nuch blocking, disruption and disorganization of vascular tissues as the
;iant cells in the susceptible roots. The other abnormalities, such as for-
nation of lateral roots in infection sites, were also observed in both the
esistant (Fig. 3) and the susceptible peanuts.


21








PHILIPPINE PHYTOPATHOLOGY


I.


I,

I


;Pfr


Fig. 2. Enlarged view of giant cells. A) Giant cells in the root of susceptible
peanut; B) Giant cells in the root of resistant peanut.


VOL. 7


^s


..


4 IJ11 q
r^(.<


^


-r


3
F ?:'hr









SA511LLJU, JZ AL.. JLAINUI I- kI5IALNLA


Attractiveness of resistant ana susceptiole peanut roots to M. napta. -
Table 4 shows the average nematode recovery from each side of the split
pots, 7 days after inoculation. When no plants were grown on each side
of the pot (NP/NP), an average of 53.3 nematodes were found in one
side and 61.7 in the other. In the R/NP treatment, the nematodes found
in the soil of the R side were 2.6 times more than in the soil of the NP
side. The total number of nematodes (in the soil and in the roots) found
in the R and NP sides were 47.7 and 13.3, respectively. Of the total
number of nematodes in the R side, 27.3% was recovered from the roots.
In the S/NP treatment, the recovered nematodes from the soil of the
NP side were 1.6 times more than those from the soil of the S side.
The total numbers of nematodes in the S and NP sides were 101.7 and
31.3, respectively. Of the total number of nematodes found in the S side,
81.3% was in the roots. In the R/S treatment, 1.5 times more nematodes
were found in the soil of the R side than in the soil of the S side. The
total number of nematodes found in the soil and roots in the R side
was 39.0 and 151.3 in the S side. The percentages of nematodes recovered
from the roots in the R and S sides were 29.0 and 88.1, respectively.































Fig. 3. Tonitudinal section of a galled root of resistant peanut. Note the forma-
**-_ -1 i ___ f .1 ** j .


11-v iJ










C~fLPIj.iYZ T53a.r AfI~ tlnJLAJ'.


L '"-


Fig. 4. Longitudinal section of a galled root of resistant peanut.

DISCUSSION

The hypersensitivity of certain plants to root-knot-nematode infection
hac relllt~drl tn thP death nf nPmatncltc within 9.4 rlav aftrPr inlAuilatinn












todes in the resistant than in the susceptible peanut 1-30 days after
inoculation could not be attributed to the death of nematodes in the
root tissue but rather to their inability to enter the host plant. Thus,
a pre-infection phase of resistance in peanut was experimentally demons-
trated. The reduced number of nematodes entering resistant roots, with
the resultant decrease in esophageal secretions, probably accounted for the
delayed formation of smaller galls in these plants than in the susceptible.
A random movement of nematodes in the absence of plant roots was
demonstrated. No obvious difference in nematode counts was obtained
between the two unplanted sides of a pot 7 days after an inoculum was
placed at the middle. However, when a resistant or a susceptible plant
was grown on one side of a. pot and none on the other, more nematodes
were consistently found on the side with a plant than on the side with-
out a plant. The attractiveness of peanut roots to M. hapla was, there-
fore, evidently demonstrated. Susceptible plants appeared to be ~more at-
tractive than resistant plants. This was indicated by the number of
nematodes recovered; there were 3.9 times more nematodes on the side of
the pot where a susceptible plant was grown than on the side where a
resistant plant was grown. This concurs with the observation of Griffin
(1969) that susceptible alfalfa seedlings were more attractive to M. hapla
than resistant alfalfa seedlings. Resistance to M. hapla at the root sur-
face of peanut was suggested when only 27 to 29% of the nematodes that
were found on the side of the pot with a resistant plant was inside the
roots, compared to 81 to 88% in the susceptible.
The recovery of significantly more nematodes in the young than in
the old plants of Arachis spp. P-246, P-258, and A. hypogaea 'Spantex'
suggests that a mature peanut plant is more resistant to M. hapla than
a young peanut plant as has been the case in tea to M. brevicauda Loot
(Loos, 1953) and in lima beans to root-knot nematodes (Barrons, 1939).
This type of resistance may be due either to a mechanical exclusion by
the mature root system, or to the greater synthesis of repellent or toxic
substances by old plants than young plants. Significantly lower gall ratings
were observed in the old than in the young plants of Arachis spp. P-246
and P-258; however, this was not observed in plants of A. hypogaea 'Span-
tex.' This result suggests a difference in response to nematode secretions
between the two resistant species mentioned and the susceptible Spantex.
Since plant age did not also affect the galling and the number of nema-
todes found in Arachis sp. P-237, it is possible that the nature of resistance
in this species is different from that in Arachis Spp. P-246 and P-258.
The post-infection phase of resistance in peanut to M. hapla was:









PHILIPPINE PHYTOPATHOLOGY


periods. .Available hypotheses concerning this type of resistance seem in-
adequate: to explain the present findings. For instance, hypersensitivity
which is common in plants resistant to root-knot nematodes, has not been
detected in the present study. Also, no basic histological differences between in-
fected resistant and susceptible peanut roots were observed. Since the histolo-
gical studies were made 30 days after inoculation, earlier determinations of ana-
tomical differences should have been attempted to interpret the results obtain-
ed. Groups of giant cells in the resistant peanut roots incited by a single
nematode (Fig. 4) were observed. This is in contrast to Barrons' (1939)

TABLE 4. Average nematode recovery from each side of split pots 7 days after
ihboulationh
No. of nematodes recovered
'Tieatmeintb Side of pot
examined Soil Roots Total
NP 53.3 53.3
SNP/NP -
NP 61.7 61.7

R 34.7 (72.7) 13.0 (27.3) 47.7
f/NP
NP 13.3 13.3

S 19.0 (18.7) 82.7 (81.3) 101.7
...S/NP
NP 31.3 -31.3

R/S R' 27.7 (71.0) 11.3 (29.0) 39.0

S 18.0 (11.9) 133.3 (88.1) 151.3
.a Average of 3 replicates.
SbNP, no plant; R, resistant (Arachis sp. P-246); S, susceptible (A. hypogaea
'Sparitex'').
c Numbers in parentheses are percentages based on total counts per side.

proposal that gall and giant cell formation in resistant plants is due to
the feeding of a large number of larvae in a limited area of a root, such
iat the root is unable to synthesize enough neutralizing substance to
counteract the large amount of nematode secretions. The relative num-
ber of giant cells incited by each nematode in the roots of susceptible
peanut plants was the same as in resistant plants. This indicates that
the inhibition of normal nematode development and reproduction in the
roots could not be attributed to lack of favorable response of the host to
nematode secretions; any other physiological incompatibility between the
resistant host and the parasite could have caused similar inhibition. The
results further indicate that, as in pre-infection resistance, post-infection
resistance increases :as: the plants grow older. Ths is evidenced by the
presence of a. significantly lower percentage of mature nematodes in the


[VOL. 7










CASTILLO, ET AL.: PEANUT RESISTANCE


old than in the young resistant plants. A change from an inhibitory tc
a lethal effect after prolonged host-parasite co-existence probably accounts
for the decline in nematode population as infection progresses.


The present findings suggest that the nati


ire of post-infection phase of


root-knot nematode resistance in peanut differs from that found in other
plants. The present findings may serve as a basis for the identification
and/or determination of similar resistant reactions to root-knot nematodes
in other plants.

LITERATURE CITED

BARRONs, K. C. 1939. Studies of the nature of root-knot resistance. J. Agr. Res.
58: 263-272.
BRODIE, B. B., L. A. BRINKERHOFF, & F. B. STRUBBLE. 1960. Resistance to the root-
knot nematode, Meloidogyne incognita acrita, in upland cotton seedlings. Phyto-
pathology 50: 678-677.
CHITWOOD, B. G. & B. A. OTEIFA. 1952. Nematodes parasitic on plants. Ann. Rev.
Microhiol. 6: 151-184.
CHRISTIE, J. R. 1936. The development of root-knot nematode galls. Phytopathology
26: 1-22.
CmaISTIE, J. R. 1946. Host-parasite relationships of the root-knot nematode, Heterodera
marioni. II. Some effects of the host on the parasite. Phytopathology 36: 340-352.
CHRISTIE, J. R. 1949. Host-parasite relationships of the root-knot nematodes, Me-
loidogyne spp. III. The nature of resistance in plants to root-knot nematodes.
Helminthol. Soc. Wash. Proc. 16: 104-108.
nr -A T T R6 Tl C T- IQ^Q tl.:.tnnn^ ^J s.... l:1:r .. 1. -1Q -n-- 1-- -_*_


tode in tomato and sweet potato. Phytopathology
DROPKIN, V. H. & P. E. NELSON. 1960. The history


GRIFFIN, G. D. 19(
root-knot nematc


43: 290. (Abstr.).


9. Attractiveness of resistant and susceptible alfalfa to stem and


Luas . . tO. itiliuugyne urevwaiuua n. sp., a cause or root-Knot ot mature
tea in Cyelon. Helminthol. Soc. Wash. Proc. 20: 83-91.
MALO, S. E. 1965. Histological studies on the nature of resistance of "Okinawa" and
"Nemaguard" peach rootstocks to Meloidogyne javanica (Treub). Nematologica 11:
43 (Abstr.).
MCBETH, C. W., A. L. TAYLOR, & A L. SMITH. 1941. Note on staining nematodes
in root tissues. Helminthol. Soc. Wash. Proc. 8: 26.
RIGcs, R. D. & N. N. WINSTEAD. 1959. Studies on resistance in tomato to root-knot
nematodes and on the occurrence of pathogenic biotypes. Phytopathology 49:
716-724.
RHODE, R. A. 1960. Mechanisms of resistance to plant-parasitic nematodes, p. 447-453.
In J. N. Sasser and W. R. Jenkins [ed.], Nematology; fundamentals and recent
advances with emphasis on plant parasitic and soil forms. Univ. North Carolina
Press, Chapel Hill.
SAss, J. E. 1964. Botanical microtechnique. 3rd ed. The Iowa State Univ. Press,
Ames, Iowa. 228 p.
SASSER, J. N. 1954. Identification and host-parasite relationships of certain root-knot
nematodes (Meloidogyne spp.). Univ. Md. Agr. Exp. Sta. Tech. Bull. A-77, 31 p.
TYLER, J. 1941. Plants reported resistant or tolerant to root-knot nematode infesta-
tion. U. S. Dept. Agr. Misc. Publ. 406, 91. p.


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PRELIMINARY STUDY OF THE TRANSMISSION OF PHILIPPINE
TOMATO LEAF CURL VIRUS BY BEMISIA TABACI

M. L. RETUERMA, G.O. PABLEO, AND W.C. PRICE
Plant Laboratory Aide, Plant Pest Control Officer, and FAO Virologist, Bureau of
ant Industry, Guinobatan Experiment Station, Guinobatan, Albay.

ABSTRACT
A disease of tomato (Lycopersicon esculentum Mill.) -referred to here as
Philippine tomato leaf curl (PTLC) -has been a serious problem in Albay
Province since 1968. We found the disease to be caused by a virus- or virus
-like pathogen -which is transmitted by the whitefly Bemisia tabaci (Genn.)
and by grafting, but not by mechanical means. The causal agent is not iden-
tical with either tobacco leaf curl virus (TLCV) or tomato yellow leaf curl
virus (TYLC). B. tabaci transmitted PTLCV after an acquisition-feeding period
as short as one hour. Having acquired the virus, the whitefly transmitted it
in an infection-feeding period as short as 3 min. A minimum of two white-
flies transmitted the virus after suitable acquisition and infection feeding periods.
The maximum level of transmission was obtained with 10-20 whiteflies.



INTRODUCTION

In 1968 farmers in the province of Albay brought our attention to
disease of tomato (Lycopersicon esculentum Mill.) that reduces yields
y 50-80%. We refer to the disease here as Philippine tomato leaf curl
PTLC). It is now so prevalent in this province that tomatoes can be
rown commercially only on newly cleared land previously cropped to
baca or other plants that prevent the growth of certain types of weeds.
udy of the disease revealed that it is infectious, is transmitted by the
hitefly Bemisia tabaci (Genn.), and is distinct from tobacco leaf curl
TLC) of the Philippines (Martinez, 1961a, 1961b; Olivares and San Juan,
)66; San Juan, 1958). On the other hand, the disease has much in comr
ion with the tomato yellow leaf curl (TYLC) of Israel (Cohen and Har-
az, 1964; Cohen and Nitzany, 1966). The results of some preliminary
investigations of the disease are reported in this paper.

SYMPTOMATOLOGY

PTLC is characterized by curling or upward cupping of young leaves
Fig. 1), by yellowing of the leaves particularly their margins and by
breaking of immature fruit with yellow blotches. Plants with these symp-
ims become very much stunted and cease to fruit. They may be in-









PHILIPPINE PHYTOPATHOLOGY


Fig. 1. Curling and upward-cupping of leaflets of a tomato plant infected wit
Philippine tomato leaf curl virus. Natural infection in the field.

fected in the seedbed as well as in the field. Infected seedlings do no
produce flowers; those infected in the flowering stage produce few flower
and small fruit. Plants are not killed outright but may linger for severs
weeks in a stunted, unthrifty condition. New growth may develop afte
the initial shock phase, but it is smaller than normal and more yellowed
The time for symptoms to develop in experimental infected plants varie
from 10-15 days.


50












he screenhouse, the plants did not develop symptoms of PTLC, sug.
ng that sweet potato is not a natural host of the PTLC pathogen.
Insect cages 1-2 feet tall and 4-6 inches in diameter were constructed
t celluloid or from finely woven dacron gauze around a supporting
framework. Neither type of cage was very satisfactory for work with
eflies because the flies tended to cluster at the top of the cage. Thus
cages were not satisfactory for short seedlings but only for those tall
Igh to reach nearly to the top of the cage.
Small cages were made from Nalgene vials, size 65 (1 inch in dia-
r, 2.5 inches long). The top and bottom end of the vial was re-
ed. A square of dacron gauze was used to cover the top opening
a gauze sleeve about 2 inches long was connected to the bottom
ing. A small hole was punched into the side of the tube and closed
a cotton plug; whiteflies were introduced into the cage through
opening. Young leaves at the top of the test plant were introduced
the cage through the gauze sleeve, the bottom of the sleeve then
g tied to the stem on which the leaf was borne. Since the whiteflies
closely confined in such small cages, they easily found the leaves
rhich to feed. The cage was supported by being tied to a stick im-
ted in the soil of the pot (Fig. 2).

PROCEDURES AND RESULTS
Mechanical transmission trials- Young tomato leaves showing charac-
ic symptoms of PTLC were chopped and ground in a mortar in the
nce of a 0.2M solution of K2HPO4. The resulting slurry was mixed
a little 320 mesh Carborundum and rubbed by hand with a gauze
over leaves of young test plants, 10-15 plants of each species other
tomato being used; 29 plants of tomato were tested. Equal numbers
plants of each species were used as controls. None of the plants be-
diseased. The species used were: Chenopodium amaranticolor Coste
eyn., Stacytarpheta jamaicensis (L.) Vahl., Solanum melongena L.,
5ersicon esculentum Mill., Nicotiana glutinosa L., N. tabacum L.,
ra sp., Cucumis sativus L., Ageratum conyzoides L., and Synedrella
fora Gaertn. In these tests, PTLC was not transmitted by mechanical
lation.
Transmission by grafting. The disease was readily reproduced in
0o plants by grafting them either by side or approach grafts
. ^. f . * ^.r_*. -..-- --1.--. *T'-I ^l ..--- -_. -r.- -*








bU2IDT inmUvr VUAVWATHlT nrfV


Fig. 2. An illustration of the small cages used for studying transmission of Phili;
pine tomato leaf curl virus by Bemisia tabaci.

expanded leaves. The mosaic and ring;pots were reproduced by graftin
other tobacco plants with scions from tobacco plants having these symj
toms. The PTLC syndrome was not reproduced in tomato plants grafted wit
scions from such diseased tobacco plants. When tobacco plants were grafte
with scions from a tomato plant that had been infected with PTLC b
the insect vector, they remained symptomless. The PTLC agent could n(
be recovered from such tobacco plants by grafting to tomato seedlings.
The results suggest that tobacco plants are not susceptible to th
PTLC agent, but that field grown diseased tomato plants often contain
a ringspot virus. This virus may possibly enhance the symptoms produce
by the PTLC pathogen.
Transmission by B. tabaci. Whiteflies in groups of 10-20 were a
lowed to feed on a source plant for 24 hr and then transferred to seedlir
test plants in pots as follows: 20 of tomato, 21 of N. glutinosa, 10 <
tobacco, 13 of Datura sp., 24 of Ageratum conyzoides, 18 of Synedrella n
diflora, 10 of Elaeis guineensis Jacq., 14 of Capsicum annuum L., 3 <


32









3s. 1 & 2] RETUERMA ET AL: TOMATO LEAF CURL 33

id 4 of Vinca rosea L. They were allowed to remain on the test plants
itil they died. After 12 days, 19 of the tomato plants developed PTLC
mptoms but neither the control plants nor test plants of the other species
d, even though kept under observation for many more days. The re-
Its demonstrated transmissibility of PTLC to tomato by B. tabaci.
Acquisition feeding period. Whiteflies in groups of 10-20 were allowed
feed on a source plant for 1, 3, 6, 9, and 14 hr, respectively, and then
insferred to tomato seedlings where they were allowed to remain. Each
oup was placed on a single seedling; three seedlings were used for each
ne period. Two of the three seedlings infested with whiteflies that had
i acquisition feeding period of 1 hr and 3 hr, respectively, developed
if curl. All the seedlings infested by groups that had fed for 6, 9, or
: hr developed the disease. The results show that B. tabaci can pick
> the pathogen of PTLC within an acquisition period as short as 1 hr.
Infection feeding period. Groups of 10-20 whiteflies were allowed
feed on a source plant for 24 hr and then transferred to test plants
here they were allowed to feed for 3, 6, 15, 30, 45, 60, 120, or 540 min.
three tomato seedlings were used for each time period and an equal number
plants were held as controls. Two of the three seedlings fed on by
ruliferous insects for 3 min developed PTLC; all the seedlings fed on
r insects that had a longer infection feeding period developed symptoms.
he results demonstrate that the pathogen can be transmitted in an in-
ction feeding period as short as 3 min.
Number of whiteflies needed for transmission. Groups of 10-20 white-
ies were allowed to feed for 24 hr on a source plant. After the acquisi-
an feeding, a single whitefly was transferred to the first plant, two to a
cond, and so on to eight on the eighth plant. They were allowed to re-
ain on the test plant until they died. Plants fed on by 2 or more viruli-
rous whiteflies developed typical symptoms of PTLC. The maximum
vel of transmission was obtained with 10-20 whiteflies.

DIscussION
The results obtained in this investigation lead to the conclusion that
TLC is caused by a virus or virus-like pathogen transmitted by Be-
isia tabaci and by grafting but not by mechanical means. The pathogen
apparently not identical with the tobacco leaf curl virus that occurs in
e Philippines, for it did not infect tobacco, N. glutinosa, A. conyzoides,
S. nodiflora, which were reported (Olivares and San Juan, 1966) to be
sceptible to tobacco leaf curl virus.
The PTLC pathogen resembles closely, but is not identical with,
mato fellow leaf curl virus of Israel. The latter is reported to infect









PHILIPPINE PHYTOPATHOLOGY


Datura stramonium L. ,N. glutinosa, and N. tabacum (Cohen and Nitzn
1966) whereas PTLCV did not. Moreover TYLCV did not infect test ph
on which viruliferous whiteflies fed for 15 min (Cohen and Nitzany, 19
whereas PTLCV was transmitted by B. tabaci after an infection feed
period of only 3 min.
B. tabaci has been abundant in Albay Province at least since 1968.
anticipate therefore that PTLC will be a problem for tomato growers
the province for some to come. There are no known sources of resist
to the leaf curl pathogen and consequently a program of breeding for rn
tance is presently out of the question.
Work needs to be done to find the weed host of PTLC. Obviot
there is a reservoir of PTLC virus in the weed population.

LITERATURE CITED
COHEN, S., & I. HARPAZ. 1964. Periodic rather than continual acquisition of a
tomato virus by its vector the tobacco whitefly (Bemisia tabaci Gennadius).
tomol. Exp. Appl. 7: 155-166.
COHEN, S., & F. E. NITZANY. 1966. Transmission and host range of the tomato yel
leaf curl virus. Phytopathology 56: 1127-1131.
MARTINEZ, A. L. 1961a. The leaf curl of tobacco in the Philippines and its tr
mission by whiteflies (Bemisia sp.). Phil. J. Agr. 26: 27-31.
MARTINEZ, A. L. 1961b. Experimental transmission of leaf curl disease of tobs
in the Philippines. Phil. J. Agr. 26: 93-99.
OLIVARES, F. M. & M. O. SAN JUAN. 1966. The transmission virus-vector relat
ship and host range of tobacco leaf curl virus. Papers presented at the Divisi4
Meeting on Plant Protection, 11th Pacific Science Congress, Tokyo, p. 283-291
SAN JUAN, M. O. 1958. Occurrence of the leaf curl disease of tobacco in the Ph
pines. Philippine Agriculturist 41: 527-529


34













ADEi;MIViNI UVi 11IiLUi LUb6 iUI IU ISAUTCIKIAL
LEAF STREAK OF RICE

O. S. OPINA AND O. R. EXCONDE

Agronomist and Associate Professor and Chairman, Department of Plant Pathology,
P. College of Agriculture, College, Laguna E-109.
This study was supported in part by Rice Project 3.3.

ABSTRACT
Yield losses in PB 76-113, IR-8 and C4-63 due to bacterial leaf streak were
studied at 3 stages of inoculation and at 3 disease intensities. The reduction
in yield during the wet season was 8.3, 13.5 and 17.1% and 1.5, 5.9 and
2.5% during the dry season at disease intensities 1, 2 and 3, respectively.
However, the reduction in yield was statistically insignificant.



Bacterial leaf streak caused by Xanthomonas translucens f. sp. oryzae
rdesimo is one of the most common leaf diseases of rice in the Philip-
ies. If infection is severe, there is an extensive drying of the leaves.
whether this drying of the leaves would cause reduction in yield is not
own. Information on the yield losses due to leaf streak is necessary
:ause such knowledge would provide a sound basis for controlling the
ease.
An objective estimate of losses caused by plant diseases has been the
)ject of many investigators. Padmanabhan (1963) and Ogawa, et al.
967) measured yield loss by comparing the difference in yield between
eased and healthy plants. Chenulu, et al. (1966) determined yield loss
groundnut due to mosaic in terms of reduction in size of pod and weight
kernel. Mathur, et al. (1964a) estimated the yield loss due to barley
ipe in terms of number of tillers, number of grain in spike and yield
a sipke per plant. Peturson (1958) measured losses due to rust by the
ference in yield between a highly resistant variety and a susceptible variety,
ile Johansen (1963) working with spring barley affected with Erysiphe
iminis DC. used highly resistant, semi-resistant and very susceptible varie-
i. Rangaswani and Subramanian (1967) also used resistant and susceptible
-ieties to measure loss due to rice blast.
The correlation of yield loss and the different degrees of infection are
o used as basis for estimating yield loss. Greaney (1933) estimated
ses in yield from cereal diseases by correlating percentage of infection









PHILIPPINE PHYTOPATHOLOGY


and yield in a single standard variety. Similar method was used by Jer
nings (1963) on hoja blanca disease of rice and Mathur, et al. (19641
on paddy blast.
Because of lack of a more accurate and quantitative assessment c
yield loss due to bacterial leaf streak, this study was conducted at th
lowland rice field of the UPCA Central Experiment Station, College, Lagun
to determine the yield loss caused by X. translucens on susceptible, intel
mediate and resistant varieties of rice at 3 stages of inoculation and
different disease intensities.

MATERIALS AND METHODS
Planting and care of plant. Twelve-day old seedlings of PB 76-11!
IR-8 and C4-63 were raised by "dapog" method. Three seedlings wer
transplanted to each hill in the lowland rice field at a distance of 20 x 2
cm. Nitrogen from ammonium sulfate (21%N) was applied at the rat
of 60 kg per hectare; 30 kg were applied at transplanting and 30 kg a
panicle initiation period. Recommended cultural practices for lowlan,
rice were followed to insure a high yield.

Inoculation. Inoculation was done at 4 and 8 weeks after tran
planting and at panicle initiation, respectively. For each stage of growth
disease intensities 1, 2 and 3 were attained by inoculating 25, 50 ani
75% of the leaves of the total hills in each plot. This was made by it
during the leaves with Carborundum dust and then spraying with a ba4
trial suspension from 48-72 hour-old cultures of X. translucens f. sp. oryza
Gathering of data. Harvesting was done when 85-95% of the grain
were fully ripened. After threshing, the grains were sun-dried to attain
an average of 14% moisture content. To determine the yield loss a
different disease intensities and stages of inoculation, the grain sample
were weighed and compared with the control.

RESULTS AND DISCUSSION
Since there was no significant interaction in yield between the
stages of inoculation and disease intensities, the yields obtained from th
3 stages of inoculation were pooled.

PB 76-113 (Susceptible). The yield obtained from each of the
disease intensities was reduced during both seasons (Table 1). During
the 1968 wet season, the mean yield of the control was 463.6 g per 1.3
sq. m, while the mean yield from intensities 1, 2 and 3 was 424.9, 400,
and 383. 9 g, respectively. These represent a respective yield loss of 8.!
13.5 and 17.1% from intensities 1, 2 and 3. In the 1969 dry season, the yiei


36









PINA SC LXCONDE: KICE LEAF 5'


eaucuon or i.D, -.Y ana .b97c was obtained from disease intensities 1,
Sand 3, respectively. The reduction in yield during both seasons, how-
ver, was statistically insignificant.

TABLE 1. Yield loss of PB 76-113 as affected by X. translucens at 2 planting seasons
1968 Wet Season 1969 Dry Season
Intensity Yield Yield
(g/1.85 sq m) % Loss (g/1.35 sq m) % Loss

0 (control) 468.6 693.9 -

1 424.9 8.3 683.3 1.5

2 400.0 13.5 652.8 5.9

3 383.9 17.1 676.1 2.5

a Figures represent average of 3 replicates and 3 stages of inoculation.

IR 8 (Intermediate). The mean yield from each disease intensity
during each season was slightly reduced in yield (Table 2). Reductions
i yield of 3.2, 9.7 and 9.6% were obtained from intensities 1, 2 and 3,
respectively, during 1968 wet season. During the 1969 dry season, reduc-
ions in yield of 5.8 and 4.4% were observed from intensities 2 and 3,
respectively. These differences in yield losses, however, were statistically
significant.

TABLE 2. Yield loss of PB 76-113 as affected by X. translucens on 2 planting
asonsa
1968 Wet Season 1968 Wet Season
Intensity Yield Yield
(g/1.35 sq m) % Loss (g/1.35 sq m) % Loss

0 (control) 720.0 653.2

1 697.0 3.2 668.6 -

2 650.2 9.7 630.0 5.8

3 650.6 9.6 634.7 4.4

SFigures represent average of 3 replicates and 3 stages of inoculation.

C4-63 (Resistant). During both seasons, no significant reduction in
eld was obtained from the 3 disease intensities when compared to the
mntrol (Table 3).


37









38 PHILIPPINE PHYTOPATHOLOGY [VOL.

TABLE 3. Yield loss of C4-68 as affected by X. translucens on 2 planting season
1969 Dry Season 1969 Dry Season
Intensity Yield Yield
(g/1.35 sq m) % Loss (g/1.35 sq m) % Loss

0 (control) 561.2 558.9 -

1 580.0 588.9 -

2 552.4 1.03 578.9 -

3 601.1 565.9 -

aFigures represent average of 3 replicates and 3 stages of inoculation.

Although the yield losses of the different rice test varieties duri.
both seasons were statistically insignificant, the degree of bacterial le
streak infection has an ultimate influence on the percentage loss in yiel
The yield loss increased correspondingly with the increase in infection
Chenulu, et al. (1963) found that the loss in yield of grains due to He
minthosporium blight of maize is directly proportional to the intense
of the disease. The same result was reported by Chenulu, et al. (196
in ground nut mosaic, and Mathur, et al. (1964a) in their study of yie
losses due to rice blast.
The decrease of functional leaf area and/or the premature drying
the leaves due to infection may explain the reduction in yield. Go
(1965) claimed that severe leaf blast causes a decline in the number
ripe panicle and reduction of grain weight.

Difference in yield loss from the 3 test varieties was observed. F
76-113, a susceptible variety, gave the highest yield loss. IR-8 intermediatet
gave a very slight reduction while no significant reduction was noted
C4-63 (resistant). These differences in yield loss were due to the different
in varietal reaction to bacterial leaf streak. Mains (1930) found that
wheat variety (Fulcaster) susceptible to rust incurred higher loss than
resistant variety (Webster). Similar study by Johnston (1931) showed th
leaf rust of wheat reduced yield by 51.5% on susceptible variety compare
to 22.0% on resistant variety. Recently, Exconde, et al. (1968) foul
that rice blast reduced yield from 12.7 to 67.2% on susceptible varied
(IR-8), but no substantial reduction in yield on moderately resistant varic
(IR-4) and resistant variety (IR-60).
The insignificant reduction in yield on IR-8 and C4-63 could
attributed to the fact that these plants can tolerate the disease. Sir












































uNs, E. B. I au. mttect or lear rust (ruccmta trtncma rlcKS.) on ylela or wneat.
J. Agr. Res. 40: 417-446.


^^













PLANT PARASITIC NEMATODES IN CORN-GROWING AREA
II. LUZON AND VISAYAS

J. J. WALAWALA AND C. P. MADAMBA
Instructor, Department of Agronomy and Assistant Professor, Departmel
Entomology, respectively, UPCA.
Paper presented at the Second National Pest Control Conference, Zaml
City, May 8-5, 1971. A portion of a thesis submitted by the senior author t
UPCA Graduate School for the degree of M.S. in Applied Zoology.

ABSTRACT

Nematode surveys in corn areas of Visayas and Luzon conducted in 196
and 1970, respectively, identified 13 plant parasitic nematode genera assc
cited with corn. Those isolated from soil samples were: Pratylenchus, Hell
cotylenchus, Rotylenchus, Scutelonema, Tylenchorhynchus, Xiphinema, Meloidc
gyne (larvae), Trichodorus, Hoplolaimus, Hemicycliophora, Paratylenchus, Cr
conemoides, and Aphelenchus. Most common and widespread in distribution:
were Helicotylenchus and Tylenchorhynchus. Pratylenchus, Hoplolaimus, and Sct
tellonema were not as widespread but occurred in more than 50% of the total
soil samples collected. Majority of the nematode genera were encounter
in Cebu while the least was noted in Camarines Sur. Paratylenchus wa
encountered only in soil samples from Cebu.
Galling was not observed in corn roots although larvae of the root-kno
nematodes were recovered from the soil samples.



INTRODUCTION

Plant parasitic nematodes constitute one of the more important fa
in crop production. They have been known to cause considerable dar
on many agricultural crops. Studies abroad show that the pathol
activities of these pests can cause as much as 50% reduction in y
(Whiteheads, 1956). In terms of monetary value, such activities cost
American farmers a half a billion dollars annually (McGlohon, 1965).

A number of plant-parasitic genera have been reported to be assoc
with corn and other crops. Investigations have shown that the stunt nema
(Tylenchorhynchus maximus Allen), dagger nematode (Xiphinema ar
canum Cobb), and spiral nematode (Helicotylenchus digonicus Perry)
commonly encountered among 13 species recovered from corn field in
consin (Griffin, 1964). The lesion nematode (Pratylenchus spp.) and 1;
nematode (Hoplolaimus galeatus) were observed to be apparently resp<
ble for severe damages on corn (Rebois and Cairns, 1968).

40








Nos. 1 & 2]


WALAWALA & MADAMBA: CORN NEMATODES


Nematode surveys in the Philippines by Timm (1964) listed 14 species
of plant-parasitic nematodes belonging to 7 genera associated with corn.
Walawala and Madamba (1970) encountered 12 nematode genera associar
ted with corn in Mindanao particularly in Cotabato.
This study is a continuation of a previous study on the occurence
and distribution of plant parasitic nematodes associated with corn in the
Philippines.
MATERIALS AND METHODS
Nematode surveys were conducted in corn-growing provinces of Cebu,
Bohol, Negros Occidental, Iloilo, Camarines Sur, Albay, Laguna, and Isabela.
Surveys in the Visayas were conducted in December 1969, in Bicol Region
in March 1970, while in Isabela in June 1970. The number of soil
samples collected from each locality ranged from 6 to 10.
Soil samples were collected from the root zone of corn plants up to
6 inches deep using a garden trowel and placed in plastic bags subse-
quently upon collection to avoid loss of moisture. The samples were brought
to the UPCA where they were either immediately extracted of their ne-
matode contents or stored in the. refrigerator until ready for processing.
The nematodes were extracted from the soil samples employing a
combination of both sieving and Baermann funnel methods as described
by Christie and Perry (1951). The nematode genera were identified using
taxonomic keys. The population density of each genus was determined
hv dirwrt omluntq under a hinnocular microscne









42 PHILIPPINE PHYTOPATHOLOGY [VOL. 7

prevalent and widespread among the nematodes were: the stunt, spiral
and lesion nematodes. The population density of the lesion nematodes
was notably high in soil samples collected from Laguna. Larvae of root-
knot nematodes were also present in appreciable numbers in the soil sam-
ples collected. However, no root galls were observed in corn roots col-
lected.
The nematode fauna of soil coming from Isabela appeared more varied
than elsewhere. On the other hand, soils from Camarines Sur contained
the least nematode genera.
More nematode genera were isolated from soils collected in the corn
growing areas of the Visayas. The 13 nematode groups identified from
this region are listed in Table 2. The survey showed that majority of
the genera were identified from soils coming from Cebu. On the other
hand, the least number came from soils gathered in Bohol. As in Luzon,
the prevalent nematodes encountered were the spiral and stunt nematodes.
The lesion nematodes appeared in lower population densities but were as
widespread in the various sampling sites except in Bohol.
The root-knot larvae were also plentiful from soils collected although
corresponding corn root samples collected were devoid of galling caused
-by the organism. There were no root-knot nematode larvae recovered
from soils obtained from Bohol.
The population level of the pin nematode (Paratylenchus sp.) was ex-
ceptionally high but it was only in Cebu where this organism was found.

TABLE 2. Occurrence of plant parasitic nematodes associated with corn in four
provinces in Visayas

Nematode Per cent frequency/400 cc soil sample
Nematode
Genera Cebu Iloilo Negros Occ. Bohol

Helicotylenchus 47.91 19.60 37.20 9.10
Tylenchorhynchus 9.94 37.60 8.40 12.10
Pratylenchus 5.84 4.30 5.10 0
Rotylenchus 0.62 4.00 7.60 3.00
Scutellonema 2.61 1.50 1.20 5.60
Hoplolaimus 2.24 3.10 2.00 0
Meloidogyne (larvae) 0.68 1.00 9.70 0
Xiphinema 0 2.30 2.00 0
Hemicycliophora 0.50 0 0 0
Paratylenchus 5.03 0 0 0
Trichodorus 2.47 0 0 0
Criconemoides 0.27 0 0 0.80
Aphelenchus 3.59 0 0 5.20









WALAWALA & MADAMBA: CORN NEMATODES


The survey indicate existence of wide variety of nematode genera in
corn-growing regions particularly in intensified areas of Isabela and Cebu.
Most prevalent among them were the stunt and spiral nematodes. The
lesion nematodes were not as extensive in distribution but they occur in
appreciable numbers in the soil samples collected. Previous surveys in
the corn areas of Mindanao has shown similar findings (Walawala and
Madamba, 1970). Since these studies show that these nematodes, notably
Pratylenchus coffeae and Tylenchorhynchus martini are most destructive to
our current corn varieties (Walawala 8c Madamba, 1971), it is apparent that
the nematodes are causing untold damages to the crop each year. The need
to control these pests to enable our farmers to realize potential yields is
in order.

LITERATURE CITED
CHRISTIE, J. R. & V. G. PERRY. 1951. Removing nematodes from soil. Proc. Helmin-
thol. Soc. Wash. 18: 106-108.
GRIFFIN, G. D. 1964. Association of nematodes with corn in Wisconsin. Plant Dis.
Reptr. 48: 458-59.
MCGLOHON, N. 1965. Room and board for nematodes costs farmers a half a billion
dollars annually. Crops and Soils 10.12.
REBOIS, R. V. & E. J. CAIRNS. 1968. Nematodes associated with soybean in Alabama,
Florida and Georgia. Plant Dis. Reptr. 52: 40-44.
TIMM, R. W. 1964. A preliminary survey of plant parasitic nematodes of Thailand
and the Philippines. Sambhand Printing Press. Bangkok, 71 p.
WALAWALA, J. J. & C. P. MADAMBA. 1970. Plant parasitic nematodes in corn-grow-
ing areas in Mindanao. Proc. First Nat. Pest Control Conference 1970: 147-153.
WALAWALA, J. J. & C. P. MADAMBA. 1971. Studies on the pathogenicity of species
of Pratylenchus, Tylenchorhynchus and Helicotylenchus on corn. Proc. Second Na-
tional Pest Control Conference 1971: 8.
WHITEHEADS, A. C. 1956. Plant parasitic nematodes important pathogens in tropical
agriculture. East African Agr. J. 22: 92-96.


Nos. 1 & 2]














PATHOGENICITY AND TOXICITY OF CRYPTOMELA
flT ITr A 1- 117 ITTT T WOO 1 A IT 1WV


A. C

Supervising Plant Patholog
Department of Plant Pathology
Portion of a Ph.D. thesis p:



Cryptomela acutispora
root tissue of healthy and


PIZARRO AND D. C. ARNY

st, Bureau of Plant Industry,
University of Wisconsin, Madis4
esented to the Graduate School, I

ABSTRACT

i. Beyma was constantly isolated
infected Black Hulless barley ai


symptoms in plants. wnen cruae toxins or tneir purlneu iorms are applo
to the plants, a part or the whole disease syndrome may be induced. Gat

44













by virtue of the toxin that penetrates the host tissue.
Pathogenic microorganisms are known to synthesize toxins that induced
symptoms on susceptible plants (Gaumann, 1954; Luke and Wheeler, 1955;
Meehan and Murphy, 1947). Victorin produced by Helminthosporium
victoria was responsible for the initiation since this fungus alone is too weak
to establish infection in healthy tissues even in susceptible varieties (Meehan
and Murphy, 1947). Ludwig (1957) showed that the relatively nonspecific
toxin produced by H. sativus conditioned barley to invasion, whereas spores
in the absence of toxin initiated no infection. This paper presents evi-
dences of the pathogenicity and toxicity of Cryptomela acutispora on bar-
ley.
MATERIALS AND METHODS
Root and soil isolations were made from healthy and barley yellow-
dwarf virus (BYDV)-infected Black Hulless (BH) barley and California
Red (CR) oat plants grown in the field and in the greenhouse. Plants
in the greenhouse were grown in 4-inch clay pots with field soil and main-
tained at 24 C. Some pots with field soil but unplanted were used as
sources of isolation. Waksman's medium (Alexopoulos and Beneke, 1962)
was used in the isolation and culture of the fungi. For every liter of this
medium, three grams of Agrimycin were added to inhibit bacterial growth.
Soil adhering to the roots of barley and oats was removed and pul-
verized. A gram of soil (dry weight) was added to 9 ml of sterile water
in test tubes and vigorously shaken. Further dilutions were made from
this solution. From the 1 x 103 dilution, 1 ml was pipetted and poured
into a Petri dish with 10 ml of solidified medium. The liquid was
first allowed to seep for 12 hr before inverting the plates for incubation.
Counts of fungal colonies were done on the third day using a Quenec
colony counter.
Young seedlings as well as fully grown plants were inoculated with
a three-week old spore suspension of Cryptomela by using a camel's hair
brush, spraying with a DeVilbiss atomizer, rubbing the leaves with a clean
piece of cheesecloth, or drenching the soil. Inoculated plants were either
placed in moist chambers for at least 24 hr or immediately transferred to
the greenhouse.
Reisolations were made from the leaves and roots of inculated plants.
Spots on the foliage of barley and Tenderbest bushbean were cut into
small pieces and plated. The roots were first washed with tap water and
rinsed with sterile water and then cut into 6-mm section and plated.










PHILIPPINE PHYTOPATHOLOGY


of fungous culture, 10 to 20 ml of distilled water was added and shaken
thoroughly. The spore suspension was filtered through two layers of filter
paper. Portions of the filtrates were centrifuged to further eliminate spores
and then autoclaved for 15 min. The toxin contained in the filtrates
was extracted by adding one part of chloroform to every 10 parts of the
sample. The chloroform extract was dried by passing a stream of air.
The crude preparation was dissolved in water and dried in the oven at
60 C. The toxic activity of these toxin preparations were bioassayed on
leaves, roots and seeds of barley and oats.

RESULT AND DISCUSSION
The fungus, Cryptomela acutispora v. Beyma, was constantly isolated
from roots and rhizospheres of healthy and BYDV-infected California Red
oats. It was also isolated from the soil but in lesser number (Table 1).

TABLE 1. Average number of fungal colonies isolated at weekly intervals from the
soil and rhizosphere of healthy and BYDV-infected Black Hulless barley and California
Red oats planted in the field
Average Number of Coloniesa
Weekly Rhizosphere
Isolations Barley Oats Soil
Healthy Infected Healthy Infected
First 72 137 21
Second 66 157 38
Third 47 84 140 224 36
Fourth 109 57 89 173 32
Fifth 33 46 13 14 30
Sixth 37 31 60 52 34
Seventh 43 38 41 76 29
a Each figure represents the average from 5 dilution plates. Each figure multiplied
by 10,000 would give the approximate number of fungi in a gram of soil on a dry
weight basis.

Weekly isolations from the rhizosphere of greenhouse-reared healthy and
BYDV-infected BH barley plants gave an almost constant number of fun-
gous colonies. The number of colonies isolated from the rhizosphere of
healthy oats reached as high as 300 times as that from barley rhizosphere,
and on the soil (Table 2). Generally more Cryptomela colonies were ob-
tained from CR oats than those from BH barley. In both barley and
oats, field and greenhouse isolations revealed the presence of more Crypto-
mela colonies in the healthy than in the infested rhizosphere of plants.
The optimum temperature for fungous growth was 32 C. At tempe-
ratures above 32 and below 24 C, growth was auite slow Acervuli were


fVOL. 7











of healthy and BYDV-infected Black Hulless barley and California Red oats raised in a
greenhouse at 24 C

Average Number of Colonies*
WeeklyR h i z o s p h e r e
Weekly
Isolations Bar le y Oats Soil
Healthy Infected Healthy Infected

First 0.8 1.2 1.3
Second 3.2 291.4 1.6
Third 0.9 1.9 308.2 177.2 2.2
Fourth 3.0 1.0 142.4 41.4 4.1
Fifth 0.6 0.9 373.2 5.2 0.8
Sixth 1.0 12.6 6.0 6.8 1.0

Each figure represents the average from five dilution plates. Each figure multi-
plied by 10,000 would give the approximate number of Cryptomela colonies in a gram
of soil on a dry weight basis.

produced at optimum and high temperatures but not at 12 C or less. Cul-
-tures held at low temperatures when transferred to room temperatures re-
sumed normal growth with the appearance of yellow pigments and the
formation of acervuli. The most intense pigmentation was observed at
20 C; it faded out as the temperature rose or dropped.
When grown in Waksman's liquid medium and incubated at dif-
ferent temperatures, Cryptomela produced abundant mycelium at 24 C
at the end of three weeks. At 32 C, mycelial production was lower
than at 12 C (Fig. 1.).
In all cases, infection occurred when spore suspensions were rubbed,
sprayed or brushed on leaves of BH barley, regardless of whether the
inoculated plants were incubated in humidity chambers or not. Infection
started in the form of small spots that appeared in 3 days after inocula-
tion; each spot turned brownish and surrounded by a chlorotic halo. It en-
larged slowly and coalesced to form larger spots. As the disease progressed,
the chlorotic halo enlarged and the whole leaf appeared chlorotic (Fig. 2).
Infection was severe on old leaves. More spots appeared on the distal
half than on the basal half portions of infected leaves.

Infection of the inoculated roots of BH barley usually appeared as
brown sections at or near the base of the roots. Root inoculation caused
stunting of the plants and inhibition of root elongation. In some cases,
emerging leaves appeared bleached.


- -... .. .-1


-- ----








PHILIPPINE PHYTOPATHOLOGY


[VoL. 7


Fig. 1. Dry weight of Cryptomela acutispora v. Beyma after 3 weeks in liquid
Waksman's medium incubated at different temperatures.


Fig. 2. Symptoms on Black Hulless barley inoculated with Cryptomela sp. spore
suspension and its metabolite. The two leaves on the left ae control, two in the middle
were rubbed with metabolite and two on the right rubbed with spore suspension.









PIZARRO & ARMY: CRYPTOMELA ON BARLEY


On leaves of inoculated Tenderbest bushbean, the presence of brown
spots which were more pronounced on the lower surface, was the first
indication of infection. From these spots, a brown network following the
veins was sometimes produced. On this host, both the old and young
leaves were susceptible. Acervuli were formed on infected leaves; they
appeared as dark gray pustules.
Inoculation of leaves of barley varieties Oderbrucker, Traill, Larker
and Trophy did not result to infection. Also, inoculation of the oat
varieties Beedee, California Red, Garland and Portage gave negative re-
sults. Likewise, no infection resulted when leaves of Golden Bantam
sweet corn were inoculated. The isolated fungus was reisolated from
the leaves and roots of inoculated plants.
In attempts to prove the pathogenicity of C. acutispora to barley and
oat plants, the different methods of inoculation induced typical symptoms
on BH barley plants. Incubation in a moist chamber for 48 hr, however,
did not enhance the development of symptoms, suggesting that a toxin
elaborated by the fungus might be involved in the development of the
disease.
The metabolites obtained after filtration and centrifugation when ap-
plied to BH barley leaves by rubbing induced symptoms resembling those
produced by inoculation with spore suspension. The autoclaved filtrates
when inoculated to the leaves of BH barley by robbing also induced symp-
toms, indicating that the toxin is heat resistant. Symptoms produced on
BH barley leaves after separate inoculation with spore suspension, filtered
and centrifuged metabolite and autoclaved preparations were identical.
Preparation of the toxin rubbed on the leaves of Tenderbest bush-
bean induced symptoms of brown spotting similar to that induced by ino-
culation with spore suspension on this host. However, preparations of the
toxin rubbed on leaves of Golden Bantam sweet corn and barley varieties Oder-
brucker Traill as well as oat varieties Beedee, California Red and Portage
did not produce symptoms.
The effect of toxin on germination of seeds was studied. Seeds of
BH barley when immersed in the toxin preparation did not germinate;
seeds placed on toxin-treated filter paper germinated poorly (Fig. 3).
The germination of different varieties of barley, oats and wheat exposed
to the toxin preparation gave varying results. The germination of oat and
wheat varieties was not affected; some of the barley varieties were slightly
affected.
The toxin applied in barely roots was still active at dilution 1 x 106
but inactive at 1 x 107, Growth of barely plants was suppressed at dilu-
tions of I x 104 or less. The effect on root elongation in oats was very


Nos. 1 Sc 2]










DZ uT TDDTmhw IDuvrn AIYTruT r-V


Fig. 3. Appearance of Black Hulless barley seedlings from Cryptomela toxin-treat4
seeds, incubated at 20 C. The six seedlings on the left are control and the six <
the right are from seeds treated with toxin at 1 x 108.

severe at dilution 1 x 104. Higher dilutions, however, had no effect. T
toxin has no effect on shoot elongation of oats. It seems that the toxi
is more potent against root elongation than shoot growth of barley and oat

The filtrates, when extracted with chloroform, yielded a yellow gun
my material upon evaporation. This material was not soluble in xylen
95% ethyl alcohol, acetone or chloroform. It was, however, soluble i
water. Dissolving it in water and drying in an oven resulted in the same gun
my material. Biological assays of the chloroform extract showed that
toxic factor was present. It caused spotting on leaves of BH barley an
Tenderbest bushbean even after autoclaving, suggesting that it is he;
-t-i-i


Kt









PIZARRO gc ARMY: CRYPTOMELA ON BARLEY.


LrrERATRE CITED

ALEXOPOULES, C. J., & E. S. BENEKE. 1962. Laboratory Manual for Introductory
Mycology. Burgess Publ. Co., Minneapolis, Minn. 199 p.
CoomE. M. C. 1871. Handbook of British Fungi. Vol. I. McMillan and Co., London.


GAUMAN, E. 1954


Toxins and plant disease. Endeavor 13: 198-204.
I. TIMONDS. 1962. Funei from rhizosphere of bananas in Honduras.


Can. J. Bot. 40: 1371-1377.
KATZNELSON, H., A. G. LOCKHEAD, & M. I. TIMENIN. 1948. Soil microorganisms and
the rhizosphere. Bot. Rev. 14: 543-587.
LUDWIc, R. A. 1957. Toxin production of Helminthosporium sativum P. K., and B.,
and its significance in disease development. Can. J. Bot. 35: 291-303.
LUKE, H. H., & H. E. WHEELER. 1955. Toxin production by Helminthosporium vic-
toriae. Phytopathology 45: 453-458.
MEEHAN, F., & H. C. MURPHY. 1947. Differential phytotoxicity of metabolic products
of Helminthosporium victoria. Science 106: 270-271.
PrEm~ BEN, J. L., S. LUND & R. S. FILMER. 1963. Control of barley yellow dwarf in
winter oat by a systemic insecticide. Plant Dis. Reptr. 47: 470-473.
RovIA, A. D. 1956a. A study of the development of root surface microflora during
the initial stages of plant growth. J. Appl. Bacteriol. 19: 72-79.
RovIRA, A. D. 1956b. Plant root excretions in relation to the rhizosphere effect. I.
The nature of root exudate from oats and peas. Plant and Soil. 7: 178-194.
ROVIRA, A. D. 1956c. Root excretions in relation to the rhizosphere effect. II. A
study of the proportion of the root exudate and its effect on the growth of micro-
organisms isolated from hte rhizosphere and control soil. Plant and Soil. 7:
195-208.


Nos. 1 & 21








-( M I I


ROHM AND HAAS PHILIPPINES, INC.
RM. 504 SIKATUNA BLDG., 6762 AYALA AVE., MAKATI, RIZAL
P. O. BOX 263, COMMERCIAL CENTER, MAKATI, RIZAL, PHILIPPINES
TEL. NOS. 88-63-90/88-05-33/88-47-11


'~~1












CHEMICAL CONTROL OF DOWNY MILDEW OF CORN:
I. THE USE OF PROTECTANT FUNGICIDES

S. C. DALMACIO AND O. R. EXCONDE
Instructor and Associate Professor, Department of Plant Pathology, College of Agricul-
ire, University of the Philippines.
This study was supported by UPCA grant No. 236a.

ABSTRACT
Four chemicals applied at different spray intervals were evaluated for the
control of downy mildew of corn. Duter applied at 2, 6, and 10 days, plus
Dithane M-45 applied at 4, 8, 12, 14, and 16 days after corn emergence effec-
tively controlled downy mildew. The effectiveness of Duter was attributed to its
eradicative and protective effects.


Downy mildew caused by Sclerospora philippinensis Weston is the
aost destructive disease of corn in the Philippines. Results of an exten-
ive study on chemical control of downy mildew from 1962-1966 showed
hat no fungicides effectively controlled the disease; most of the fungicides
tested, however, inhibited germination of the fungous spores. On the
their hand, recent study on the mode of penetration and infection of the
athogen revealed the systemic nature of the disease. This finding led
o the reexamination of the use of fungicides for its control. This paper
reports a re-study on the effect of protectant fungicides in controlling corn
owny mildew.

MATERIALS AND METHODS
Experiment 1. Three trials were conducted from November 1969 to
larch 1970, to determine the efficacy of 4 fungicides against downy mildew.
eeds of sweet corn were planted in seedbeds (1.2 x 20 m) at the rate of
0 seeds per meter row; distance between rows was about 20 cm. Rando-
lized complete block design with 5 treatments and 3 replications was
sed. Prior to planting of the test plants, sweet corn were planted around
he experimental area and were inoculated to serve as natural source of
noculum. The chemicals used were Dithane M-45 (80% zinc, manganese,
thylene bisdithiocarbamate), Daconil 2787 (75% terachloroisopthalonitrile),
)ifolatan 4 Flowable (experimental fungicide) and Duter (20% triphenyltin
ydroxide). These were applied at 2.4 g, 2.4 g, 2.0 ml, and 1.0 g/liter,
respectively. In the second and third trials, Daconil 2787, Difolatan 4
lowable and Duter were applied at 1.5 g, 1.5 ml, and 0.75 g/liter, res-

53












actively. Spraying was started at emergence for 3 consecutive days and
ten every other day thereafter for a period of 21 days.
Experiment 2. A field test was conducted in January 1970, to deter-
ine the effect of Dithane M-45 alone on downy mildew. Sweet corn
eds were planted in 5 x 30-meter field plots where naturally-infected
plants were present. There were 3 replications, each plot representing
replicate. Treated and non-treated plants were in alternate rows from
ne end of the plot to the other. The rate of Dithane M-45 and the
praying schedule used in Experiment 1 were followed.
1u7Ao-;,_n f T A r-;l 1 Q7O I ct-Al tn Tltoyrmirn tho pffprt of














sticker was added at the rate of 4 ml for every liter of spray suspension.
Data were taken about 50 days from planting, except in Experiment 3
where the data were taken about 30 days from planting. Plants showing
the systemic symptom (increasing chlorotic area on succeeding younger
leaves) were considered infected.

RESULTS
The results of 3 trials in experiment 1 is shown in Table 2. In the
first trial, all the fungicides greatly reduced the downy mildew in-
cidence. Except Dithane M-45, the other 3 fungicides showed high degree
of phytotoxicity. Plants sprayed with Difolatan and Daconil 2787 showed
stunting and twisting of leaves while plants sprayed with Duter showed
localized drying of the leaves; these portions were on the whorl at the
time of spraying. In the second trial, the concentrations of the 3 phyto.
toxic fungicides were reduced. Results showed that none of the fungicides
gave good control of the disease. In the third trial, only Duter reduced
infection percentage but phytotoxicity was still noted.

TABLE 2. Effect of chemicals on downy mildew infection

Percentage Infection
Fungicide
Trial 1 a Trial 2 b Trial 3 e

Dithane M-45 31.1 99.7 97.0

Daconil 2787 12.8 99.4 98.0

Difolatan 4 flowable 14.4 91.8 91.2

Duter 1.0 98.3 d 69.5

Untreated 87.0 100.0 98.3

a Average of 3 replications per trial.
b The 4 chemicals were applied at the rate of 2.4 gm, 2.4 gm, 2 ml, and 1.0 gm per
liter of water, respectively.
e Daconil 2787, Difolatan and Duter were applied at 1.5 gm, 1.5 ml, and 0.75 gm
per liter, respectively.
d Appliation of Duter was terminated after 3 applications because of high phytotoxi-
city.

Field trial on the effect of Dithane M-45 showed that this chemical
slightly reduced infection percentage of downy mildew (Table 3). Com-
pared with the unsprayed plants, control of downy mildew due to Dithane
Al A K ,-- -C9 17 af















4'k'INL rn-lurAil-ULUt..


'L. I








DALMACIO & EXCONDE: CORN DOWNY MILDEW


Experiment 4, combination of Duter and Dithane M-45, appreciable
reduced infection. Unsprayed plants were greatly stunted compared witd
the sprayed plants (Fig. 1). Duter applied at a higher concentration
tended to be more effective (Table 5). This effectiveness of Duter-Dithant

TABLP 7. Number of spraying of Duter-Dithane M-45 combination and percentage ol
downy mildew incidence
UPCA VAR. 3 Sweet corn a
Spraying
No. of I II III Ave. I II III Ave.

12 17.84 29.61 19.91 22.91 21.68 17,16 35.63 .24.85
8 41.33 22.66 24.34 29.44 33.96 29.17 27.47 30.2(
4 27.54 39.32 39.50 35.45 25.52 9.42 21.50 18.81
2 89.11 92.53 92.27 91.30 48.15 37.43 34.26 39.94
0 94.98 99.27 100.00 98.08 66.26 59.57 50.49 58.71

a The 5th and 6th sprayings were missed because of a typhoon.

M-45 combination was further confirmed on subsequent field trials (Ex
periment 5). Tables 6 and 7 show that downy mildew was greatly reduced
by 4 spray applications (2 applications each of Duter and Dithane M-45'
although 8 and 12 applications were far better. Population in the unsprayed
plots was greatly reduced (Fig. 2) and infected plants that survived wer
stunted and produced narrow leaves (Fig. 3).


Nos. 1 & 2









58 PHILIPPINE PHYTOPATHOLOGY [VOL. 7





















Fig. 2. Plots showing the effect of spraying on plant population. Note the reduced
population of the unsprayed plants treatmentt V of the second and third relicatiom).





















Fig. 3. Unsprayed infected plants (left, foreground) showing narrow leaves. Sprayed
plants are on the right (foreground).

DISCUSSION
Results in Experiment 1 (trial 1) and Experiment 2 clearly indicate
that, under moderate epiphytotic conditions, any of the 4 fungicides tested
and probably. any other fungicide capable of inhibiting germination of









DALMACIO & EXCONDE: .CORN DOWNY MILDEW


be applied early (at emergence time) to prevent or minimize penetration,
at least in the first 3 weeks of corn growth. This finding may partly
explain the failure of previous tests to control the disease effectively by
applying protectant fungicides 1-2 weeks after planting or about 3-10 days
after emergence. Because successful penetration and infection can take
place anytime from emergence up to 3 weeks after planting and because
of the systemic nature of the disease, no protectant fungicide has been
found to control the disease effectively in earlier studies (Dalmacio and
Exconde, 1969). Sun and Lai (1966) also implied that failure of Dithane
M-22 to control downy mildew caused by S. sacchari was due to late spray
application.
The effectiveness of Duter can be attributed to its eradicative and
protective effects. The mechanism of its eradicative effect can be illustrated
as follows: Duter causes necrosis or drying of the sprayed leaves. Since
this pathogen is an obligate parasite, death' of the leaf tissues would result
to the death of the pathogen that have already penetrated. Furthermore,
these necrotic areas completely shut off subsequent invasion of the pathogen
through these portions. As to its protective effect, Duter can effectively
inhibit germination of the fungous spores. Exconde et al. (1967) found
that Duter and some dithiocarbamate-containing fungicides (Dithane M-22
and Parzate) have similar effects on spore germination of S. philippinensis.
These effects of Duter could then explain why it is more effective than
Dithane M-45 which has only a protective effect. This observation seems
to be in parallel with that on plants attacked by corn seedling maggots,
Antherigona oryzae Malloch; infested plants showed lesser infection thar
those not attacked. Continuous application of Duter is detrimental to the
growth of corn plants, thus, an equally effective protectant fungicide such
as Dithane M-45, has to be applied during later sprayings.
Spraying with Duter 3 days after emergence did not control the disease
(Table 3). This could be attributed to its late application. Assuming that
penetration of the fungus occurs at emergence, it is possible that the patho-
gen has already invaded the leaf portions (leaf sheath) below the necrotic
areas induced by Duter. An evidence to support this contention is the
appearance of disease symptoms on Duter-sprayed on the same day the
symptom on unsprayed plants appeared.
Based on the above results, 3 applications of Duter starting 2 days
after corn emergence, plus 5 applications of Dithane M-45 can be re-
commended for controlling downy mildew. The authors believe that this
number of applications can still be reduced to give the same degree of
control. This may be accomplished by widening the spray intervals during
later sprayings. Study on this aspect is, therefore, suggested.


Nos. 1 & 2]













LITERATURE CITED
DALMACIO, S. C. & O. R. EXCONDE. 1969. Penetration and infection by Sclerospora
pinensis Weston on cornm Philippine Agriculturist 52: 35-52.
EXCONDE, O. R., S. A. RAYMUNDO, F. D. FUENTES, R. M. PAYSON, A. C. MECAI
& F. A. AQUILIZAN. 1967. Testing of fungicides for the control of downy
and screening of corn varieties, hybrids and inbred lines for downy mildew resi
Final Technical Report. Grant number FG-PH-10. UPCA, College, Laguna
ippines (Mimeographed). p.
SUN, M. H. & W. Y. LAI. 1966. Evaluation of fungicides for protecting con
downy mildew infections. Proc. Third Inter-Asian Corn Improvement Worksh,
dian Agr. Res. Inst., New Delhi, p. 188-202.










PHYTOPATHOLOGICAL NOTE


RENIFORM NEMATODE, ROTYLENCHULUS SP., IN MUNGO,
SOYBEAN AND PEANUT SOILS AT THE UPCA CENTRAL
EXPERIMENT STATION

M. B. CASTILLO
Assistant Professor, Department of Plant Pathology, U.P. College of Agriculture,
college Laguna.

Nematode survey conducted in August, 1970 in the plantings of mungo,
oybean and peanut at the UPCA Central Experiment Station revealed the
>revalence of the reniform nematode, Rotylenchulus sp. (Table 1). Among
heie crops, mungo appeared to be the most favored host; this nematode
vas found in all of the 34 composite soil samples obtained from the
hizosphere, with 79.4% very heavily infested. The nematode was also
found in all of the 37 composite soybean samples, with 54% very heavily
nfested. Peanut seemed to be the least favored host since the nematode
vas found only in 5 out of the 21 composite samples collected, only 4.8%
of which was very heavily infested. In the infested soils, the average
number of nematodes in a 300 cc soil sample from mungo, soybean and
peanut was 1395, 808 and 129, respectively. In all the crops, nematode
nfestation was observed to be associated with root necrosis; the severity
vas somewhat directly proportional to the number of nematodes present
a the soil. The correlation between nematode infestation and plant growth

ABLE 1. Prevalence of Rotylenchulus sp. at the UPCA Central Experiment Station

Ave. no. of Severity of Nematode Infestationb
No. of infested nematodes
Host plant samples per infested Very
sample Trace Light Moderate Heavy Heavy

Mungo 34/34 1395 0 3 1 3 27

Soybean 37/37 808 2 4 3 8 20

Peanut 5/21 129 1 2 0 1 1

SEach sample consisted of 300 cc of soil made up of three 100-cc subsamples
ich from a single plant. Numerator represents samples containing the nematode; deno-
minator represents samples collected.
b Figures represent number of samples in each category based on nematode counts
er sample: trace, 1-30; light, 31-120; moderate, 121-240; heavy, 241-450; very heavy,
ver 450.

A1















nd peanut and bacterial pustule on soybean. Examination of stained
ifected roots revealed the female namatodes in the feeding position (Fig. 1),
n evidence that this nematode is parasitic on these plants. More egg
passes were observed in stained mungo roots, suggesting that the nematode
as a better reproduction in this crop than in either soybean or peanut.
Trace infestations of other known plant parasitic and non-plant parasitic
ematode< species were also observed. In the mungo soils, the parasitic
ematodes found were Meloidogyne and Hemicycliophora, and the non-para-
itic ones were Acrobeloides, Alaimus, Aphelenchus, Cephalobus, Chilo-
lacus, "Dorylaims," Iotonchus, Mononchus, Rhabditis and Tylenchus. The
,arasitic nematode genera Helicotylenchus, Hemicycliophora, Hoplolaimus,
nd Xiphinema, and the non-parasitic genera Alaimus, Aphelenchus, Atylen-
hus, Cephalobus, "Dorylaims," Mononchus, Paraphelenchus, Rhabditis and
"ylenchus constituted the other nematode populations in soybean soils.
The other nematode associates of peanut soils were the parasitic Helicoty-
nchus, Hemicycliophora, and Pratylenchus, and the non-parasitic Alaimus,
Iphelenchus, "Dorlaims," and Tylenchus.

Studies on species identification and pathogenicity of the Rotylenchulus
violate and its interaction with mungo, soybean, and peanut should be con-
.ucted before formulating effective control measures. Although only trace
infestations of the other plant parasitic nematodes were observed, rotation
,f crops including non-hosts, can be practised to avoid population build-
ip, since the pathogenicity of some species of these nematodes on mungo
Agor, 1971; Anonymous, 1960) and on peanut Welles & Cooper, 1961) had
ieen confirmed.

LITERATURE CITED
COR, S. 1971. Reactions of several breeding lines of mungo to infection by Me-
loidogyne incognita. Undergraduate Thesis, U. P. College of Agriculture, College,
Laguna. 24 p.
NONYMOUS. 1960. Index of plant diseases in the United States. USDA Crop Res.
Div., Agr. Handbook No. 165. 531 p.
fELLES, J. C., & W. E. COOPER. 1961. Peanut nematode diseases. North Carolina
Agr. Ext. Ser., Ext. Folder No. 136-61.










Sa n i I a
SWORN STATEMENT
(Required by Act 2580)
The undersigned, SJLVINO D. MERCA, business manager of PHIL
SPINE PHYTOPATH9LOi.0Y published Semi-annually in English at UPCA, Coll
laguna after bainu 'je duly sworn in accordance with law, hereby submits
o ollo t n'ae of ownership, management, circulation, etc., which is required
t-5bM ae- Vamended by Commonwealth Act No. 201.
Name Address
Editor: AGUSTIN N. PORDESIMO ................ UPCA, College, Laguna
Business Manager: SILVINO D. MERCA .......... BPI Research Division, Ma
Owner & Publisher: Philippine Phytopathological Society UPCA, College, Laguna
Printer of Publication: Community Publishing, Inc. .... 2131 Dr. Manuel M. Can
Office of Publication: UPCA Dept. of Plant Pathology College, Laguna
In case of publication other than daily, total number of copies printed
circulated of the last issues dated January & June, 1970.
1. Sent to paid subscribers ................ .................. 120
2. Sent to others than paid subscribers .......................... 480
T o t a 1 .................................... 500
SILVINO D. MERCA
Business Manager
SUBSCRIBED AND SWORN to before me this 5th day of April, 1972,
Los Baiios, Laguna, the affiant exhibiting his/her Residence Certificate No. A-4031
issued at Los Bafios, Laguna on April 5, 1972.
PEDRO G. BANZON
Notary Public
Doc. No. 326 (Until December 3, 1972)
Page No. 77 BIR No. 5889392E
Book No. III Los Bafios, Laguna
Series of 1972 January 12, 1972
NOTE: This form is exempt from the payment of documentary stamp tax.


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