Front Cover
 Biological control of plant pathogens:...
 Properties of the peanut stripe...
 Comparison of assessment methods...
 Bacterial blight of anthurium andreanum...
 Pathogenic variation of sphaceloma...
 Components of pathogenic variability...
 Abstracts of papers presented during...
 Poster presentation
 Back Cover

Group Title: Journal of Tropical Plant Pathology
Title: Journal of tropical plant pathology
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00090520/00032
 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 1990
Frequency: semiannual
Subject: Plant diseases -- Periodicals -- Philippines   ( lcsh )
Plants, Protection of -- Periodicals -- Philippines   ( lcsh )
Genre: periodical   ( marcgt )
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: VID00032
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 54382605
issn - 0115-0804

Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    Biological control of plant pathogens: Progress and constraints in the Philippines and other countries
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
    Properties of the peanut stripe virus in the Philippines
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
    Comparison of assessment methods for rice sheath blight disease
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 24a
        Page 24b
    Bacterial blight of anthurium andreanum Lind.
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
    Pathogenic variation of sphaceloma batatas saw in sweet potato
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
    Components of pathogenic variability and host resistance to erwinia chrysanthemi Burk., McF., & Dim. in corn
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
    Abstracts of papers presented during the 21st anniversary and annual convention of the pest control council of the Philippines held at the Sugarland Hotel, Bacolod City from May 7-10, 1990
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
    Poster presentation
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
    Back Cover
        Page 71
        Page 72
Full Text








Sbscrprtios: Communications dmMo i
meat of Pint Patholog, UPL., Colge. Lag
anualy, is the ofical osuan of the Phippi
members in ood standing md Sustaiing Amoei
$15.00 per copy elsewhere, post free md I
Phytopthological Society Inc.: Informatio re
upon request. Pihe Orge: The editoial bol
amount for each published page commensurate up
or supporting institutions. Advertisements: Rat
endorsement of any staPement of claims made in

- Pm


Buamsi Manqr

Board Membr
Bowd Member
hnmadae Past Presidet

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Associgar Edbor
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beamd to e TREASURER. PP S. c/o Depqt-
m hiLppie L ryt.opmdola publild =i-
,yaqtpmd idi Soctie, ha. It i scat fse to
Foer ou es, its 0 per copy (dmileic)- m
in adrame. Nmtb in t e P5tp e
g am amip wE be sppied by the Scmay
sas the riast ta caise ss pI t
he payment capabilties of their research project
lay be secured from the Business Manager. No
ertisements is assumed by this Journal or by the

Phil, Phytopatnologl

91 90 Phii. Phyto h m. or



Searca Professorial Chair Lecture Aeli,
Auditorium, UPLB College of Agriculture, C

Professor of Plant Pathology and Directo:
of Agriculture, University of the Philippines al

Recognizing the hazards of pesticides to
man and his environment, many countries in
the world today are considering biological
control as the best alternative to chemical
control of plant pests and diseases. In
response to this need, more research funds
are allocated by governments of different
nations to attract and support more scientists
to develop biocontrol technologies against
major pests and diseases of economic crops.
While other countries have already made
significant advances in the biocontrol of plant
pathogens, the Philippines is just at the initial
stage of development especially of the
biocontrol of fungal, bacterial and viral
pathogens. It has, however, made some
substantial advances in the study of
biocontrol of plant parasitic nematodes which
started in the late 1960's.

This paper, therefore, attempts to
review the state of knowledge of biocontrol
studies in the Philippines as compared with
those in other countries and discuss some of
the important problems and constraints that
affect the growth and development of
biocontrol technologies.


Most of the studies done on the
biocontrol of pathogens, other than
nematodes, have started only in the past few
years which were mainly preliminary in scope
and done under laboratory and greenhouse
conditions (Davide, 1990). For instance, an in



-d at the National Crop Protection Center
ge, Laguna.

Sthe National Crop Protection Center, College
)s Bafios.

showed that some species of Trichoderma
had potentials for controlling root rot and
foliar pathogens of vegetable crops. He
observed that T. glaucum showed true
hyperparasitism on hyphae of Rhizoctonia
solani and T. harzianum on Sclerotium rolfsii
On the other hand, T. viride parasitized S.
rolfsii, R. solani and Pythium debaryanum b3
adhering to the hyphae of the latter. It wa,
also shown that culture filtrates of T. viride
and T. harzianum inhibited conidia
germination ofAltemaria brassicae, A. solani,
Fusarium oxysporum f. sp. lycopersici and
Cercospora canesens by 16 to 84%. A more
extensive study was conducted by Neypes el
al. (1988) on the use of T. glaucum Abbot foi
the biocontrol of S. rolfsii causing foot rot ol
wheat. Under field conditions, it was more
effective in controlling the disease compared
with a fungicide and resulted in significant
increase in yield.
On the other hand, Rosales (1985)
showed that T. harzianum and T. aureoviride
had higher cellulolysis adequacy indices and
were rice straw decomposers than othei
Trichoderma spp. This resulted in the
reduced recovery of the sheath blight
pathogen, R. solani, from infected straws
Thus, treatment of sheath blight infected
stubbles with Trichoderma spp. reduced
occurrence of damping-off of mungbear
caused by R. solani.
Gliocladium species. constitute another
group of soil fungi investigated for theii
potential as biocontrol agents against plan
pathogens. Five isolates of Gliocladium spp
collected from different parts of the


--l p ve hyop- hloy--l~

for the control of soil-borne pathogens of
soybean. On PDA, these isolates showed
antagonistic effects against Pythium
aphanidermatum, R. solani, S. rolfsii and F.
oxysporum. When applied with a substrate
into the soil where the soybean seeds were
planted and which was inoculated 7 days
before seeding, Gliocladium isolates
controlled the incidence of P.
aphanidermatum, R. solani, S. rolfsii and F.
oxysporum by 66, 73, 75 and 65%,
On the use of beneficial bacteria for the
biological control of plants pathogens, a
more comprehensive study was conducted by
Rosales et al. (1986) at the International Rice
Research Institute (IRRI) where they tested
139 ricefield bacterial isolated against F.
moniliforme causing bakanae of rice. All the
isolates inhibited the mycelial growth F.
moniliforme in vitro. However, based on
seedling or germination tests, only 50% of
the isolates were effective in suppressing
bakanae. In farmer's field tests, treatment of
seeds with antagonistic bacteria reduced the
incidence of bakanae by 70.4 to 74.6%
comparable to 76.1% of the benomyl
treatment. This study demonstrated the
applicability of biocontrol utilizing naturally-
occuring beneficial bacteria for bakanae
While we are still barely scratching the
surface of the potentials of microorganisms
for the biological control of diseases caused
by fungi, bacteria and viruses, we have
already made substantial and more
comprehensive studies on the biological
control of nematodes. Our studies started 23
years ago when in 1967 we first isolated the
nematophagous fungi Arthrobotrys sp. and
Dactyllela from rice straw compost and
chicken manure (Cortado & Davide, 1968).
This was followed by a more comprehensive
study by Reyes and Davide (1975) resulting
in the isolation of 6 genera and 8 species of
nematophagous fungi from animal and farm
soils. Greenhouse tests of these fungi showed
that they could reduce the incidence of
rootknot on tomato caused by M. incognita by
38 to 70%. However, the isolated
nematophagous fungi were slow-growing and
difficult to mass produce for field application.
The discovery of the soil fungus,
Paecilomyces lilacinus (Thom) Samson by
Jatala et al. (1979) in Peru as egg parasite of
nematodes sparked our interest to work on it.

From 1982 to the present we have focused
our studies on P. lilacinus isolates from
Philippine soils. Under greenhouse and field
conditions, results of our studies clearly
showed the great potential of P. lilacinus for
the biological control of plant parasitic
nematodes causing diseases such as root gall
and rootknot of vegetables, fruits, and field
crops, as well as the toppling disease of
banana caused by Radopholus similis. The
efficacy of control ranges from 40 to 85%
using the most effective isolate which is now
being commercially produced by tthe
BIbACT Corporation in the Philippines.
Morever, other species of soil fungi such as
Penicillium spp., Metarhizium spp. and
Gliocladium spp. are now being explored for
their potential for biological control of plant
parasitic nematodes.


Other countries especially Japan, Taiwan,
U.SA., Great Britain and Australia have
already succeeded in developing various
biocontrol technologies against major
diseases of economic crops. For instance,
Japan has already developed attenuated
strains of viruses to control the mosaic virus
disease on tomato, sweet pepper, watermelon
and soybean through cross-protection
method (Homma, 1990). They can now
control the Fusarium wilt of sweet potato
caused by Fusarium oxysporum using a non-
pathogenic strain of the pathogen (Ogawa,
1990). The product is in powdered form
containing spores of the fungus. To protect
the sweet potato plants from the wilt disease,
cuttings of planting materials are dipped into
the solution for a few minutes before planting
them in the farm. A non-pathogenic strain of
Rhizoctonia solani has also been developed
to control root rot of sugar beet caused by
the virulent strain of the fungus. Likewise, a
technology has been developed for
bacterization of plant materials with
rhizobacteria to control diseases such as
potato scab, take-all disease of wheat, root
rot of beans and damping-off of sugar beet
(Homma, 1990). For the biological control of
diseases caused by nematodes, Japanese
nematologists are working on Pasteuria
penetrans which is a mycelial and endospore-
forming bacterium and a parasite of root-
knot and cystnematodes as a promising

Philippine Phytopathology

Vnl on

mnuary- une IvuU

loIogical lonuOI OT rilanT ramogens

nocontroi agent (Nks izawa, iyw). Af
-TD., is developing the technology.

In Taiwan, where the biocontrol program
receives one of the highest budgetary
allocations in crop protection studies from
he government, the most significant
Achievement is the reestablishment of their
papaya industry which was once wiped out by
he papaya ringspot virus disease. This is
lone through cross protection technology
Rising attenuated strain of the virus where
eedlings are sprayed with the strain in
suspension (Kao, 1990). The technology is
badly needed in the Philippines to revive our
papaya industry in Cavite and other areas in
Luzon where the disease has destroyed the
>apaya industry three years ago. Taiwan has
Iso succeeded in controlling a virus disease
Affecting passion fruit where thousands of
hectares were already affected. The
technology involves the production of virus-
ree seedlings of passion fruits and early
detection and destruction of infected plants
Chang, 1990). The recent adoption of the
technology by the growers has saved the
industry. Other biocontrol technology that
Faiwan is developing now is the use of soil
ungus Trichoderma koningii for the control
>f bean rot disease caused by Rhizoctona
olani (Liu, 1990). With biocontrol given a
tigh priority in Taiwan's crop protection
program, more advances in the technology
ire expected in the near future to benefit the
Top growers.
In the United States, successful use of
)iocontrol technology for the control of
brown gall disease of stone fruits (apple,
>each and pear) caused by Agrobacterium
umefaciens is well demonstrated. A non-
>athogenic strain of the pathogen was
discovered and developed commercially as
C84 (Kerr, 1980). The strain, if introduced
nto the infected plants can effectively control
he crown gall disease. In Australia K84 has
been genetically-improved with the
development of a new strain K1026 which is
registered for commercial use as Nogall TM,
i peat-based formulation (Jones, et al., 1990).
Another U.S. biocontrol product now in
he process of formulation is composed of
he strain Pseudomonas syringae lachrymans
L-59-66 for the biocontrol of. post-harvest
diseases of stone fruits (apple, peach and
)ear) such as blue mold caused by

-emcuaum expansum ana gray moma cause
iy Botrytis cinerea (Janisiewicz, 1990).
In Great Britain, root rot disease of
:onifers like pine trees caused by Fomes
nnosus is biologically-controlled by a
-ompetitor pathogen, Peniphora gigantea.
'he commercial products is in the form of
dehydrated tablets containing large amount
if spores of P. gigantea. It has already been
successfully applied to more than 50,000
hectares of conifer forest in Britain to protect
he plants from disease infection (Rishbeth,
The initial success of some of these
diocontrol product has undoubtedly
encouraged some private companies to invest
a research and development in biocontrol.
tome chemical companies are now beginning
o employ biologists to study microorganisms
hat have potential for biocontrol of pests and
diseases. However, there are a number of
problems and contraints that can hamper
development of a biocontrol technology.


Some of these problems and constraints
hat can seriously affect development of
Piocontrol technologies are:

Ecological and Biological Problems -
Biocontrol requires a thorough
understanding of the biology and
ecology of the pathogens as well as the
biocontrol agents. The life cycle of the
pathogen, particularly the stage where it
is highly vulnerable to attack by the
biological control agents should be
known. There is a need to know the
factors that may cause the failure of the
biocontrol agent to act on the target
pathogens in the host tissues or in the

. Specificity of Control Most known
biocontrol agents are generally specific
to a single pathogen species. The ideal
one should be able to control more than
one pathogen or against a number of
plant diseases. This will be. more
profitable to the company and
economical to the crop growers using it.

. Slow or Delayed Action on the
Pathogen The effect of biocontrol

Philippine PhytdpathoIogy Vol.26

agent is generally slow on the pathogen
compared with the action of chemical
control where its effect can be seen in a
matter of few hours. This is mainly
because the biocontrol agent has to
establish and multiply first in the site of
introduction. It usually takes some time
for the pathogen to succumb to the
attack of the biological control agents.

4. Screening Problem Usually the
tendency of scientists working on
biocontrol is to choose only one
organism that show high potential
against test pathogens mainly because of
limited funds and manpower. This
practice can definitely exclude many
isolates which may have high biocontrol
potential against other pathogens but
are just discarded.

5. Bureaucratic Regulations Some
governments require so much red tape
in giving research grants to biocontrol
projects. They require clearance and
registration of the biocontrol agents to
be studied. This will surely affect
screening work to discover organisms
with high degree of biocontrol potential.
For genetically-engineered organisms,
they may require stricter regulations but
those naturally-occurring and
commonly-known to cause no harm to
man and his environments should be
given due consideration for use in
research studies. The scientists
concerned, therefore, should be given
full responsibility in maintaining the
safe use of the organisms he is working

6. Lack of Financial and Technical
Support This is basically the problem
in many Third World countries where
there are not enough funds and
technical manpower to support research
and development of biocontrol
technologies. In most countries,
biocontrol is still at its initial stage of
development and therefore getting
adequate support funds and manpower
is still a limiting factor.

7. Lack of Program Coordination The
advancement of biocontrol studies
depends to a large extent not only on

the availability of support funds and
manpower but also in the program
structure and organization at the
national level. Realizing this problem,
some countries have already
institutionalized their biocontrol R & D
by establishing a coordinating bodies.
For instance, Malaysia has established a
National Coordinating Committee for
Biological Control, while Thailand has a
National Institute for Biological Control
to oversee the development and
operation of biological control programs
nationwide. In the Philippines, however,
our biocontrol programs are still
scattered in different institutions and
without a national body to coordinate
and rationalize the program. We hope
the Department of Agriculture will
initiate the move soon as this is the right


Some of the scientific problems and
constraints in developing biocontrol
technologies may be minimized through an
understanding of the principles by which
biocontrol agents operate in nature. As
defined by Garret (1965), biocontrol is any
condition or practice under which whereby
survival of activity of a pathogen is reduced
through the agency of any living organism
(except man himself) with the result 4hat
there is a reduction m the incidence of the
disease caused by the pathogen. There are
three general ways or types that biocontrol
may operate to suppress pathogens. These
are 1) natural biocontrol, 2) introduction of
biocontrol agents or antagonists, and 3)
biocontrol through modification of the
environment. In natural biocontrol, a
pathogen causes little or no disease in an
apparently favorable environment, or fails to
become established despite frequent
introductions into an apparently favorable
area. This is due to the constant presence and
build-up of naturally-occurring suppressive
organisms or antagonists in areas where the
pathogens are inhabiting. An example is the
failure of the root rot pathogen, Phytophthora
cinnamon of avocado, despite its presence in
the soil, to cause the disease on woody plants
in soils of rainforest vegetation of Northern

Philippine Phytdpathology

Vol. 26

January June 1990 neological control or reant remogens a

New South Wales and Southeastern
Queensland, Australia due to high organic
matter contents and nutrients in the soil
which favor the growth of beneficial
microorganisms that suppress the growth of
the pathogen (Broadbentt & Baker, 1975).

On the other hand, when pathogens are
not inhibited by naturally-occurring
microbes, biocontrol can be used by adding
or introducing more effective antagonists. A
good example is the biocontrol action of the
fungus P. lilacinus, which is introduced into
the soil where plant parasitic nematodes are
causing damage to crops (Jatala et al., 1979).
Abroad, the crown gall disease of stone fruits
caused by Agrobacterium tumefaciens is
controlled by introducing a non-pathogenic
strain of the bacterium, K84, into host tissues
(Kerr, 1980). The usual practice of effecting
biological control in the field is by
introducing antagonists into the soil or in the
host tissues.

Biocontrol through modification of the
environment is done by cultural management
of crops to favor the growth of suppressive
microorganisms which inhibit the growth of
pathogens. For example, crop rotation is
applied to maintain diverse soil
microorganisms and prevent the
development of large populations of
pathogens. Likewise, the use of organic
amendments such as the application of soil
compost or animal manure into the soil
usually favors the growth of antagonists than
pathogens, thereby reducing disease
incidence (Garrett, 1963).

Mode of Action of Biocontrol Agents

There are a number of ways by which
antagonistic organisms suppress growth of
pathogens and control diseases (Cook, 1990).
Their action could be through 1) parasitism,
2) production of toxic compounds like
antibiotics, and 3) induction of host
resistance. Some of our developed biocontrol
products directly parasitize pathogens, like
plant parasitic nematodes as in the case of P.
lilacinus. However, the microbial action
against fungal and bacterial pathogens is
..-.^11.. l I.r .,L tL- -...,..,,, 4C ~ *,

tumefaciens (K84) produces agrocin to
control the crown gall disease of stone fruits
(Jones, et al, 1990). Other biocontrol agents
do not directly affect the pathogens but the
host, instead, by inducing resistance. An
example is the use and introduction of the
mycorrhiza, Glamus fasciculatus, into the
roots of sweet orange to induce resistance of
the plant to infection by Phytophthora
parasitica causing the foot rot disease (Davis
and Menge, 1980). Likewise, the use of
mycorrhiza can also induce resistance of
tomato roots to infection by root-knot
nematodes. Another example is the use of
mild strains of mosaic viruses to induce
resistance of host plants to attack of virulent
strains of the same virus (Motoyoshi, 1990).
The microorganisms inducing resistance
generally compete with pathogens for
nutrients in host tissues and form barriers
between the host and the pathogen to
prevent penetration and infection (Cook,


An ideal biocontrol agent must satisfy
most, if not all, of the following attributes: 1)
must not be pathogenic to plants and

.. . n..

'--' "-----' -' ~'--~-"-

Philippine Phytopathology Vol.26

larger farm size; and 7) market development
of the product (Janisiewicz, 1990).

This process may take 5 to 10 years or
more and requires substantial investment in
funds and technical manpower.


Biological control of plant diseases,
though it has made some significant advances
in recent years, is still in its infant stage.
Given adequate time and support, however, it
will not be long before more biocontrol
products are introduced into the market as
safe alternatives to pesticides for the crop
growers to use. The future, therefore, is
bright for the biocontrol industry.


ALCANTARA, T.P. 1987. Antagonistic
activities of Trichoderma species against
vegetable fungal pathogens in vitro. BSA
Thesis, University of the Philippines at
Los Bafios 46 pp.

BROADBENT, P. and BAKER, K.F. 1975.
Soils suppressive to Phytophthora root
rot in Eastern Australia, p. 152-157. In
C. W. Bruehl, (ed.) Biology and Control
of Soil-Borne Plant Pathogens. Am.
Phytopathol. Soc., St. Paul, Minnesota.

CHANG, CA. and LIN, H.H. 1990.
Establishment of large scale
propagation systems for virus-free
passion fruit seedings and it uses in
controlling passion fruit virus diseases in
Taiwan. (Abstr.) International
Conference on Biological Control of
Plant Diseases and Virus Vectors, Sept.
17-21, 1990, Tsukuba, Japan, p. 55-56.

COOK, RJ. 1990. Current status and future
prospects in research and practice of
biological control. (Abstr.).
International Conference on Biological
Control of Plant Diseases and Virus
Vectors, Sept. 17-21, 1990, Tsukuba,
Japan. p 11-15.

CORTADO, R.V. and DAVIDE, R.G. 1968.
Nematode-trapping fungi in the

Philippines. Philip. Phytopathol. 14:4

DAVIDE, R.G. and ZORILLA, RA. 1983.
Biological and chemical control studies
of the potato cyst nematode found in
Madaymen, Buguias, Benguet. Philip.
Phytopathol. 19:28-35.

DAVIDE, R.G. 1990. Biological control of
plant diseases in the Philippines.
(Abstr.) International Conference on
Biological Control of Plant Diseases
and Virus Vectors. Sept. 17-21, 1990 in
Tsukuba, Japan. p. 23-25.

DAVIS, R.M. and MENGE, JA. 1980.
Influence of Glamus fasciculatus and
soil phosphorus on Phytophthora root
rot of citrus. Phytopathology 70:447-452.

GARRETT, S.D. 1965. Toward biological
control of soil-born plant pathogens, p.
4-16. In K. F. Barker and W.C. Snyder,
(eds.), Ecology of Soil-Borne Plant
Pathogens, Prelude to Biological
Control. University of California Press,

DAVIDE, R.G. 1986. Biological control
of Radopholus similis on banana with
three nematophagous fungi. Philip.
Phytopathol. 22:36-41.

HOMMA, Y. 1990. Biological control of
plant diseases and virus vectors in
Japan. (Abstr.) International
Conference on Biological Control of
Plant Diseases and Virus Vectors, Sept.
17-21, 1990, Tsukuba, Japan. p. 17-18.

JANISIEWICZ, WJ. 1990. Control of
postharvest diseases of fruits with
biocontrol agents. (Abstr.) International
Conference on Biological Control of
Plant Diseases and Virus Vectors, Sept.
17-21, 1990, Tsukuba, Japan. p. 47-49.

BOCANGEL, M. 1979. Biological
control of Meloidogyne incognita and
Gldabodera pallida on potatoes.
Nematology 11:303.

Vol. 26

Philippine Phytopathology

January -June 1990BilialCnrloPatPahgs

B.G., FARRAN, S.K. and KERR, A.
1990. Biological control of crown gall
using Agrobacterium strains K84 and
K1026. (Abstr.) International
Conference on Biological Control of
Plant Diseases and Virus Vectors, Sept.
17-21, 1990. Tsukuba, Japan. p. 73-75.

KAO, C. W. 1990. Recent Achievements on
biological control of plant diseases in
Taiwan. (Abstr.) International
Confered on Biological Control of Plant
Diseases and Virus Vectors. Sept. 17-
21, 1990, Tsukuba, Japan. p. 69-23.

KERR, A. 1980. Biological control of crown
gall through production of Agrocin 84.
Plant Dis. 64:24-30.

MOTOYOSHI, F. 1990. Virus resistant
plants transformed with virus genes.
(Abstr.) International Conference on
Biological Control of Plant Diseases
and Virus Vectors, Sept. 17-21, 1990,
Tsukuba, Japan. p. 69-73.

I.F. 1988. Trichoderma glaucum Abbot
for biological control of foot rot of
wheat caused by Sclerotium rolfsii Sacc.
Philip. Agric. 71:157-163.

NISHIZAWA, T. 1990. Biological control of
root-knot nematodes and cyst
nematodes with bacterial hyperparasite,
Pasteuria penetrans. (Abstr.)
International Conference on Biological
Control of Plant Diseases and Plant
Vectors Sept. 17-21, 1990, Tsukuba,
Japan. p. 101-103.

OGAWA, K. 1990. Biocontrol of Fusarium
wilt with non-pathogenic Fusarium
oxysporum in Japan (Abstr.)
International Conference on Biological
Control of Plant Diseases and Virus
Vectors, Sept. 17-21, 1990. Tsukuba,
Japan. p. 933-96.

REYES, T.T. and DAVIDE, R.G. 1975.
Fungi for biological control of plant
parasite nematodes. Philip. Phytopathol.
Soc. Bull. 3:55.

RISHBETH, J. 1975. Stump inoculation: A
biological control of Fames annosus. G.
W. Bruehl (ed.). In Biology and Control
of Soil-Borne Plant Pathogens p 158-
162. Am. Phytopathol. Soc., St. Paul,

ROSALES, AVELITA M. 1985. Rice straw
decomposition by Trichoderma species
and its effect on inoculum of sheath
blight pathogen, Rhizoctonia solani
Kuhn. M.S. Thesis, University of the
Philippines at Los Bafios. 112 pp.

and MEW, T.W. 1986. Biological
control of Bakanae diseases of rice with
antagonistic bacteria. Philip. Phyto-
pathol 22:29-35.

SINAGA, MEITY S. 1986. Biological control
of some soil-borne fungal pathogens of
soybeans [Glycine max (L.) Merr.] with
Gliocladium spp. Ph.D. Thesis,
University of the Philippines at Los
Bafios 170 p.

DAVIDE, R.G. 1984. Evaluation of
several soil fungi for biological control
of root-knot nematodes. Philip. Agric.

January June 1990

Biological Control of Plant Pathogensr


Fe L. Mangabi
and Rod

Portion of the senior author is M.S. The
Los Baios (UPLB), College, Laguna, Philip]
Respectively, University Researcher, I
Professor, Department of Plant Pathology, I
College, Laguna, Philippines.


Peanut stripe virus (PStV)
symptomatology, method of transm
The common symptoms oi
blotch, oakleaf pattern and stripes a
symptoms persist until crop maturi
vector (100%) of the virus. The other
A. citricola and Rhophalosiphum rn
efficiencies of 41%, 13.5%, 4.5'
transmitted the virus in a non-persis
Seed transmission on cultiv
of infection. The highest seed trans
were infected at the seedling stall
flowering stage.
Seven out of 23 plant sf
families became infected with PSt\
on Chenopodium amaranticolor a
incana, Desmodium triflorum, Glyci
Vein clearing and blotches were
The virus retained its in
inactivated upon exposure to 65C f(
infective for only 1 day if stored at
when stored in a freezer. The Phili
antisera obtained from North Caro
from the University of Georgia. I


Peanut, like any other crop, is subject t<
infection by a number of viral diseases
Among these diseases are peanut mottle
peanut stunt, peanut bud necrosis, peanut
marginal necrosis and neannt masice (Smith


Marina P. Natural
;o B. Valdez1

submitted to the University of the Philippines a
tute of Plant Breeding, Assistant Professor an
versity of the Philipppines at Los Bafios (UPLB


as isolated and characterized based on
on, host range, physical properties, and

commercial peanut are green islands or
g the lateral veins of peanut leaves. The
Aphis craccivora was the most efficient
phid species, A. gossypii, Myzus persicae,
lis also transmitted the virus at varying
and 4.5%, respectively. All species
t manner.
UPL Pn 4 varied depending on the time
;sion of 9.9% was obtained when plants
followed by plants inoculated at pre-

es representing 18 genera and seven
'he virus incited cholorotic local lesions
C. quinoa and mosaic on Crotalaria
max, Vigna unguiculata and V. radiata.
so observed on Glycine -max and V.

tivity up to a dilution of 10-4, was
.0 minutes, and the crude sap remained
m temperature (25-30C) and for 3 days
ine isolate reacted positively with PStV
a State University, from ICRISAT, and
id not react with peanut mottle virus

1972) and ringspot (Kuhn and Paguio, 1973'
that can cause extensive yield losses
Fortunately, some of these virus diseases ar
geographically restricted (Demski and Lovel
1985). In India, peanut production is severely
hampered by bud necrosis caused by tomato
sootted wilt virus (TSWV that is spread b

__ ~"'~' ~~~`-'--~ --~-~-

loO Ph- PhWomtH

Jua J

thrips. In Africa, peanut production is
restricted by groundnut rosette (GR) that is
transmitted by aphids in a persistent manner
(Bock, et al, 1970). GR is not known to be
seed-transmitted in peanuts. PMV naturally
infects peanut in all continents where the
crop is grown.
In the Philippines, only peanut mottle,
reported by Benigno in 1977, and whose
effect on growth and yield of was studied by
Pua (1978) was considered as the major virus
disease of peanut. Aside from PMV, no other
virus disease of peanut has been investigated
in the Philippines. In 1984, a new disease was
observed in the breeders plots and in other
experimental fields by a visiting virulogist
from the International Crops Research
Institute for the Semi Arid Tropics
(ICRISAT), Dr. D.V.R. Reddy. He reported
that the disease was due to peanut stripe
virus (PStV). Demski and Loveli (1985)
recognized it as a potential worldwide
problem. The virus has a higher percentage
of seed transmission that PMV which could
lead to a higher disease incidence early in the
season and ultimately to a greater yield loss.
This paper reports on the results of
studies conducted to isolate and characterize
PStV in the Philippines on the bases of
transmission, host range and symptomatolo-
gy, physical, and serological properties; and
to screen possible sources of resistance.


Virus Isolation and Propagation

Peanut .plants infected with PStV were
collected from the experimental areas of the
Institute of Plant Breeding (IPB), UPLB.
Symptoms were classified and compared with
the descriptions reported by Demski et al.
(1984). Infected tissues were homogenized in
0.05 M phosphate buffer, pH 7.2, containing
Na SO (1 g tissue: 9 ml buffer) and 1%
Celite. The extract was gently rubbed, using
the tip of the forefinger, to fully expanded
leaves of Chenopodium amaranticolor Coste
& Reyn, as this plant was reported to be a
local lesion host of PStV (Demski, et al.,
1984). Inoculated leaves were rinsed
thoroughly with water.
Single lesions were cut from the C.
amaranticolor, honiogenized similarly and
inoculated to the young quadrifoliates of 7-d

old peanut variety UPL Pn4, using a
sterilized glass rod. These inoculated test
plants were immediately rinsed with tap
water, place in mylar cages and maintained in
the greenhouse for symptom development.
Infected tissues from the inoculated
peanut seedlings were homogenized in 0.05
M phosphate buffered saline (PBS), pH 7.2,
with 1% Celite. The purity of this antigen
preparation was tested using Ouchterlony
agar gel double diffusion test in Petri plates
and the specific PStV antiserum provided by
Mr. Ver Aquino obtained from the North
Carolina State University (NCSU), USA.
After this confirmatory test, mass inoculation
of susceptible peanut seedlings UPLPn 4, was
done. The inoculated test plants were
maintained in insect proof cages to prevent
contamination by other viruses. This serves
as source of inoculum and the virus isolate is,
henceforth, referred to as Philippine isolate
of PStV.
The purity of the virus isolate was
regularly determined by repeated alternate
inoculations to both local-lesion and systemic

Characterization of PStV

Transmission Studies

Mechanical Inoculation. and Host Range.
Mechanical inoculation was effected
following the same procedure described in
virus propagation. Host range studies were
conducted using different plant species.
Seeds of each test plant were grown in pots
inside the screenhouse and mechanically
inoculated with the virus when they were
about 2-4 weeks old depending on the plant
species. A total of 3 replications with ten
seedlings per replication were used. The test
plant were maintained and observed daily for
symptom development. Back inoculation to
C. amaranticolor and serological test were
employed to confirm the presence/absence
of the virus in symptomless plants.
Grafting. Twenty potted plants grown in
insect proof cages wered used in this study.
The top of the infected peanut plant was cut
axially through the middle of its stem. After
its end had been cut into a wedge shape, the
scion from a healthy plant was inserted
tightly into this slit and the joint was then
wrapped with plastic tape. The cleft-grafted

January June 1990

Properties of the Peanut Stripe Virus

o 1M

plants were placed in insect proof cages.
Symptoms of systemic infection were
observed in the new growths of the scion.
Tops of healthy peanut plants grafted to
healthy plants served as control.
Aphid Transmission. Five aphid species,
namely, Aphis craccivora Koch., A. gossypii
Glover, A. citricola Van der Goot,
Rhopalosiphum maidis Fitch and Myzus
persicae Sulzer were reared on healthy
cowpea (Vigna unguiculata Walp.) cotton
(Gossypium hirsutum), Tridax (Tridax
procumbens), corn (Zea mays) and tobacco
(Nicotiana tabacum), respectively. To avoid
contamination, first instar nymphs were used.
The plants containing the aphids were placed
in insect-proof cages.
After 24 h, first instar nymphs were
transferred from the host plants to petri
plates and starved for Ih at room
temperature and transferred to diseased
peanut for an acquisition access time of 10-30
min. Ten viruliferous aphids were given 30
min inoculation access period, and then killed
by spraying insecticide. Plants inoculated with
non-viruliferous aphids served as control.
The test plants were maintained in insect-
proof screen cages and observed for
symptom development.
Seed Transmission. At least 1000 seeds
from PStV-infected peanut plants were sown
in seedboxes filled with sterilized soil placed
in insect-proof screenhouse. As soon as the
seeds germinated, daily observation for the
appearance of symptoms was done up to .a
period of 4-8 weeks from sowing.
Percent seed transmission was
determined by dividing the number of plants
infected over the total number of plants
multiplied by 100.

Physical Properties of PStV

The physical properties of the virus
isolate were investigated using the
procedures described by Bos et al. in 1960.
Crude sap was extracted from PStV-infected
peanut plants, cv. UPL PN4 and C.
amaranticolor was used as the indicator host
to determine specific infectivity by
mechanical inoculation.
Thermal Inactivation Point (TIP). This
was done by immersing 10 ml of the virus-
containing extract for 10 min in a hot water
bath at a temperature ranging from 50-100 C

Dilution End Point (DEP). Seven ten-
fold dilutions of the crude sap were prepared.
The infectivity of each of the diluted.extract
was determined by mechanical inoculation to
C. amaranticolor and peanut. The number of
lesions per dilution per plant was recorded.
Longevity in vitro (LIV). Virus-
containing plant extracts were placed in test
tubes. Half of the tubes were stored at room
temperature (25C) and the other half at
freezing temperature. Six seedlings of C.
amaranticolor were inoculated daily fro the
first week and at weekly intervals thereafter
until no more infection was obtained.

Serological Relationships

Serological tests were conducted using
both the Ouchterlony agar gel double
diffusion method described by Ball (1974)
and the direct antigen coating enzyme-linked
immunosorbent assay (ELISA) as used with
peanut viruses and described by Reddy
(1989) using the antisera obtained from
NCSU, ICRISAT, and. the University of

Reactions of Different Cultivars/Breeding
Line of Peanut to PStV

One hundred seven local and
introduced peanut breeding lines and
cultivars, which exhibited resistance to

lad 26

Ph~llfplne Phytopathology

muary Jun. 1900 ~pertiesof the Peanut Str~e Viiias

triping (Fig. 1). Extracts of these plants
when mechanically inoculated to C.
maranticolor elicited chlorotic lesions 7-10
lays after inoculation (DAI) but without
ystemic infection (Fig. 1A). Single lesion
extracts from C. amaranticolor, inoculated to
*eanut cv. UPL Pn4, showed systemic
ifection with symptoms that ranged from
lotches, stripe and oak-leaf pattern (Fig.

transmissionn Studies

Mechanical inoculation and Host Range.
'he virus isolate was readily transmitted by
mechanical inoculation to C amaranticolor
nd peanut. Infected peanut plants initially
exhibited systemic symptoms of light
hlorotic spots and discontinuous stripe along
ie lateral veins of young quadrifoliates 11-21
)AI. Later, these infected plants exhibited
lotch symptoms or irregular green islands
ith chlorotic tissues and darkened area
long the midvein that resembles an oakleaf.
Out of the 23 plants species belonging
S18 genera and seven families tested, seven
ave positive reactions (Table 3). The virus
cited chlorotic local lesions on C
maranticolor and C quinoa but not in C.
turale and mosaic on Crotalaria incana,
esmodium triflorum, Glycine max, Vigna
iguiculata, V. radiata, and Desmodium sp.
'ein clearing and blotches were also
observed on G. max and on V. unguiculata.
he latter also showed vein clearing, mild
:af distortion and little leaf symptoms. None
F the test plants belonging to the families
izoaceae, Compositae, Cucurvitaceae,
ralvaceae and Solanaceae as well as
olichos lablab, Phaselous vulgaris and
'cimum basilicum of Papilionaceae as found
ost of the virus.
Grafting. The virus was transmitted by
eft-grafting using either infected scion
rafted to a healthy stock or a healthy scion
rafted to an infected stock. However, the
tter became infected with the virus two
eeks earlier than the former. Grafts of
:althy control plants remained uninfected.
Aphid Transmission. Five aphid species,
unely, Aphis craccivora, A. gossypii, A.
tricola, Rhoaphalosiphum maidis and Myzus
ersicae transmitted PStV to peanut cv. UPL
n4 with varying efficiencies (Table 1). All
.00%) the test plants inoculated with

ifection, while 41% infection was noted with
iose inoculated with A. gossypii, 13.6% with
f. persicae and 4.5% with those of A.
itricola and R. maidis.
Seed Trahsmission. Seed transmission of
StV in peanut cv. UPL Pn4 was relatively
)w as determined by ocular inspection of the
terminated plants from seeds of infected
lants. The highest percentage of seed
transmission occurred from plants infected at
eedling stage (9.9%) followed by those
ifected at pre-flowering stage (4.7%). Plants
ifected at flowering stage showed 1.4% seed
ansmission (Table 2).

physical Properties of PStV

The results, as shown by the number of
:sions formed on C. amaranticolor, revealed
iat the virus is relatively unstable. The vjrus
:tAined its infectiyity at a dilution of 10" to
) but not at 10' and was inactivated upon
qposure to 65C for 10 min and its infectivity
I crude sap was only 1 day at room
:mperature (25-30C) and 3 days when
ored in a freezer (Table 4).

anuary Jun 1990

roprfies'of the Peanut Strip Virus

Philippine Phytopathology

Vol. zi

Itoms of PStV in peanut are quite PMV because of the inability of the
rent from PMV since the latter produces induce chlorotic local lesions
mic mottling with interveinal depression Amaranticolor and C. guinea.
h becomes unapparent as the foliage The physical properties of PS1
res (Kuhn, 1965). congruence with the observations
Transmission by grafting also proved to Demski and Reddy (1987) with the
i effective method. It could successfully of LIV of crude sap which revealed 1
mit the virus in less than two weeks could be stored for three days at tt
cularly if infected stock and healthy and one day at room temperature.
I were used. Since it is assumed that the Serological tests revealed that :
is carried by water in the plant it could PMV are two distinct viruses of pe;
iferred that the results obtained were former was reported to be closely i
to rapid movement of water from the BICMV and CYW while the latter
;to the scion, hence, carrying the virus
cles to the scion and consequently
ting this portion.
The results of aphid transmission
dled that A. craccivora, the cowpea aphid,
the most efficient vector of the PStV
te among the aphid species used and
i transmit the virus in a non-persistent
her. It was also observed that the virus
I be transmitted by more than one aphid
ies indicating that there was not vector
ificity. This implies that the spread of
r in the field could be aided by any of the
:mentioned species but A. craccivora
i be primarily responsible for the rapid
id of PStV. This result does not conform
, that of Screenivasulu and Demski
5) where M. persicae was the more
lent vector for both PMV and PStV than
*raccivora. The non-conformity of the
Its could be attributed to the strain of the
, or the biotvne of the anhid.

January-Jun. 1990 Properties of the Peanut Stripe Virus


BALL, E.M. 1974. Serological tests for the
identification of plant viruses. The
American Phytopathological Society.

BENIGNO, DA. 1977. Plant virus disease in
the Philippines. Proc. Symp. Trop.
Agric. Res. Sept. 1976.

and MWATHI, G.K. 1970. Groundnut
viruses. Record of research. Ann. Rep.
E. Afr. Agr. For Res. Org. for 1969.

L. 1960. Suggested procedures for
international identification of legume
viruses. T.Pl. Ziekten 66: 328-343.

DEMSKI, J.W. and LOVELL, G.R. 1985.
Peanut stripe virus and the distribution
of peanut seed. Plant Dis. 69:734-738.

SOWELL, G. Jr. and BAYS, D.C. 1984.
Peanut stripe virus- a new seed-borne
potyvirus from China infecting
groundnut (Arachis hypogea). Ann.
Appl. Biol. 105:495-501.

KADO, C.I. and H.O. AGRAWAL. 1972.
Principles and techniques in plant
virology. Van Nostrand Reinhold

KUHN, C.W. and PAGUIO, O.R. 1973.
Virus disease of peanut in Georgia.
Georgia Agric. Res. 15:11-14.

PUA, D.R. 1978. Effects of peanut rosette
and peanut mottle virus on the yield,
protein and oil content of peanut. M.S.
Thesis. University of the Philippines
at Los Bafos, College, Laguna,

G.R. and GRAYSON, R.L. 1986.
Ultrastructural cytology of peanut
infected with PStV. Phytopathology
75:1311 (abst).

REDDY, D.V.R. 1989 Training Course
Manual on the identification and the

detection of legume viruses. ICRISAT,
Patancheru 45 p.

SMITH, K.M. 1972. A textbook of Plant
Virus Diseases. Longman Grp. Ltd.
Great Britain. 684 p.

1988. Transmission of PMV and PStV
by A. craccivora and M. persicae. Plant
Dis. 72:722-723.

1986. Detailed studies on peanut stripe
and peanut yellow spot diseases. In
Proc. Fifth Groundut Res. Ann.
Meeting, Samuag Res. Sta., 19-21
March 1986, Chiangmai, Thailand.

Demski and Reddy 1987.

Fig. 1. Symptoms of peanut strope virus
(PStV), chlorotic local lesions on
Chenopodium amaranticolor (A) and oak
leaf, strope and blotches on peanut cv. UPL
PN4 (B).

January -June 1990

Properties of the Peanut Stripe Virus



Fig. 1. Symptoms of peanut stripe virus (PStV), chlorotic local
lesions on Chenopodium amaranticolor(A) oak leaf, stripe and
blotches on peanut cv. UPL PN4 (B).

Philippine Phytopathology

Vol. 26 '

VoL 28 Comparise ofr'Asmemnt Methods 15

Table 1. Efficiencies of various aphid species in the transmission of peanut stripe virus.(PStV) to
peanut c.v. UPL Pn 41

Aphid Species Number of plants infected
Total number of plants inoc.

Aphis craccivora Koch. 22/22(100)2

A. gossypii Glover 9/22 (40.5)

Myzus persicae Sulzer 3/22 (13.6)

Rhophalosiphum maidis Fitch 1/22 (4.5)

Aphis citricola Van der Goot 1/22 (4.5)

1 Aphids were starved for 1 h and given acquisition and inoculation access periods of 1 h and 30 min, respectively.
2. Means of 2 trials, wih 22 plants per trial per aphid species

Table 2. Effects of growth stage of peanut on percent seed transmission of peanut stripe virus in

No. of Seed No. of Seedlings
Growth Stage planted infected

Seedling 1,000 99 (9.9)
(10 days after
planting DAP)

Pre-flowering 1,000 47 (4.7)
(20 DAP)

Flowering 1,000 14(1.4)
(30-35 DAP)
ST--! .- --___I-A I n 1 /A\I%

Table 3. Plants tested in the host range studies of the peanut stripe virus (PStV)1



Zinnia elegans Jacq. NR

Cucurmis sativus L. NR
Cucurbita maxima Dcne. NR

Crotalaria incana L.
Demosdium triflorum (L.) DC.
Glycine max L. Merr.
Vigna radiata, L. Wilczek
Vigna unguiculata Walp.
Dolichus lablab L.
Phaseolus vulgaris L. cv. Top Crop
Ocimum basilicum L.

Gossypium hirsutum L.

Chenopodium amaranticolor Coste & Reyn.
C. quinoa Willd.
C. murale L.

Datura metel L.
D. stramonium L.
Nicotiana glutinosa L.
N. tabacum L.
Lycopersicon esculentum Mill.
Solanum melongena L.
Gomphrena globosa Mart.
Tetragonia expansa L.

mos, vc, vb, Id
mos, vc
mos, 11, Id





1 Plants were mechanically inoculated using sap extracted from peanut cv. UPL Pn4 infected with PStV

2 Legend:

mos mosaic
vc vein clearing
vb vein banding
cll chlorotic spot

Id leaf distortion
NR- No Reaction
11 little leaf

Vol. 26

Comparison of Assessment Methods

Vol. 1

mparison of Assessment Methods

Dilution end point (DEP), Thermal inactivation point (TIP), and longevity in vitro (LIV)
Af peanut strike virus (PStV1l

Table 4

Property Ave. no. of lesions

Dilution end poi


Thermal Inactivw


Longevity in Vit

Room Temperal
Freezer 3

day 1

Inoculum was pi

Average of 2 tri,





4 infected with PStV. 1


in o(

Af pean


Comparison of Assessment Methods Vol. 26

Reactions of 107 peanut lines and accessions to peanut stripe virus (PStV) using the sap
inoculation method

Lines/Acc. % Infection1 Symptoms Lines/Acc. % Infection Symptoms



IPB Pn -71-9
ICG 1703
(NC 17127)
Pn 68-187
Ace. 816
Pn 114- 7
NC 17030
Pn 12-14
Pn 83-114-52
NC 17135
NC 17133 RF
IC 16
RMP 12
IPB Pn 82-68-71

b, ol
b, ol
b, s
ol, b
b, ol
b, s
s, b
b, ol
b, s
b, s
b, s
b, s
s, b
s, b
b, s
b, s
ol, s

Pn 48-26
Pn 82-75-31
Pn 83-71-15
CES 24-2
EGM 13
UPL Pn 4
Pn 114-14
HYQ (CG) 5-30
Pn 68-4
NC 17132
IPB Pn 85-121-60

Table 5.

b, s
b, s
b, ol
b, s
b, s
b, s
b, s
b, s
mb, s
b, s
m, s
s, b
< b, s
b, ol
b, s
s, b
ol, b
b, s
b, s
ol, b
b, s
ol, b

Vol. 26

Comparison of Assessment Methods

Table 5. Con't.

Lines/Acc. %




% Infection Symptoms

HYQ (CG) 5-28
Pn 82-68-160
ICGS (E) 22
Pn 24-1

100 b, s
100 b
100 b
199 b
100 bol
100 b
100 b,s

ICGS (E) 61
ICGS (E) 27
Pn 82-70-27
HYQ (CG) 5-7

100 b, s
100 b, ol
100 b, ol
100 b
100 b,s
100 b
100 b,s

1 Mean of two trials
2 Legend:

ol oakleaf; s- stripe; Vss very severe stripe;
b blotch; and mb mild blotch

Comparison of Assessment Methods

Vol. 26


N.R. Sharma, PS. To

Respectively, Senior Scientific Officer, ]
Bangladesh (Formerly, Collaborating Researcl
Plant Pathology, IRRI, P.O. Box 933 Manila,
Specialist and Head, Crop Protection Division, ]


Five methods for assessing the intense
Rhizoctonia solani Kuhn were comp
disease progress curves of three rice (
respectively, highly susceptible, susce]
disease. The methods were % HR
Height), % DS (Percent Disease Sever
SES scale (standard Evaluation System
Area Infected). Both % HRLH anc
reproductibility and ease-of-use. Althc
it represents actual infected tissue, the
this method makes it impractical f
epidemiological studies. DI does no
sheath blight assessment because all til
after a primary source of infection w
suitable for epidemiological or yield 1i
screening for host plant resistance.


The sheat blight disease of rice caused
by Rhizoctonia solani Kuhn, Thanatephorus
cucumeris (Frank) Donk is one of th major
rice diseases in the tropical sub-tropical and
temperate region of Asia, Africa and the
Americas (Ou, 1985). The primary source of
inoculum is the sclerotium that+ survives in
field soil for more than a year. The pathogen
has a wide host range which includes weeds,
water hyacinth and other cereal and non-
cereal crops (Ou, 1985; Kozaka, 1975). It
causes lesions on the leaf sheath which are At


Sand F.M Olivares

agladesh Rice Research Institute, Gazipur,
Yellow, IRRI); Plant Pathologist, Division of
iilippines; and Supervising Science Research
ILRICE, Mufioz, Nueva Ecija, Philippines


of rice sheat blight disease caused by
-d for their ability to characterize
ivars, IR72, IR64 and IR26957-86-2,
)le and moderately resistant to the
[ (Percent Highest Relative Lesion
), % DI (Percent Disease Incidence),
ale of 0-9), and % RAI (Percent Real
o DS met the criteria of simplicity,
h %RAI is the most reliable because
ost of labor and equipment to apply
the large number of samples in
appear to be a suitable method for
s in a hill become infected very soon
established, While the SES is not
studies, it nevertheless has value in

first ellipsoid, somewhat irregular greenish-
grey and vary from 1 to 3 cm long. Sclerotia
are formed on or near these spots but are
easily detached. In the field, spots are usually
first observed near the water line when
conditions are favorable to the pathogen.
They are also formed later on the upper leaf
sheaths and on the leaf blades. Although the
etiology of rice sheat blight disease is
relatively well-studied, its epidemiology,
effect on yield and varietal resistance, to the
pathogen are not well known. An essential
element in understanding these aspects of


Assessment Methods for Rice Sheath Blight Disease

reliable method to quantify the amount of
disease present. Many methods for disease
quantification are reported in the literature
(James and Teng, 1979; Teng, 1987) and
utilize techniques ranging from visual
assessment to remote sensing of host plant
tissue. In many cases, disease symptoms are
assayed assuming that they reflect
quantitatively the growth of the pathogen in
the host (Parlevliet, 1979). Different crops
and different diseases have required specific
systems for assessment. Use of the
appropriate assessment method for a defined
objective is important to generate the
database required in epidemiological studies.
For rice diseases, a standard evaluation
system (SES) was established which included
a system for rice sheath blight (IRTP, 1980).
Other methods are in use for assessing
sheath blight intensity in screening for
varietal resistance and in epidemiological
studies, notably the Relative Lesion Height
method of Ahn et al. (1986) and a Percent
Disease Severity method (Teng, 1975).
These methods appear to be used in the
literature without any attention paid to their
original design; for example, while the SES
scales were primarily for germplasm
evaluation, they have, also been used for
studies on disease progress and yield loss.
The latter requires more precision to
discriminate between levels of disease
intensity that cause loss and it is questionable
if a scale such as the SES scale can provide
this. In our present study, the objective was
therefore to compare different assessment
methods for precision and ease of use in
quantifying sheath blight epidemic.


Rice cultivars, IR72, IR64 and IR26957-
86-2, respectively, highly susceptible,
susceptible, and moderately resistance to
sheathh blight were used in the study. Five
10-day old seedlings were transplanted into
35 cm diameter clay pots filled with a lowland
field soil (Maahas Clay) taken from the IRRI

farm Los Baiios. The pots were fertilized
with the equivalent of 80kg N/ha in two
splits, the first application was done at 20
days after transplanting and the second at the
panicle initiation stage. Four replicates, each
of 5 pots were arranged in a randomized
complete block design in the greenhouse.

Inoculum for the experiment was mass
propagated on rice-hull mixture (rice: grain
hull -1:3) using an isolate of R. solani (LR-1
from the IRRI farm) maintained on potato
dextrose agar (PDA). Heat-resistant bottles,
8 x 20 cm each, were filled to approximately
70% capacity with the rice: hull mixture,
autoclaved for 3 h at 121 C and on cooling
were inoculated with 5-day old PDA mycelial
bits of R. solani. Test plants were each
inoculated at booting stage with about 30 ml
of inocula placed at the base of each hill and
between the tillers. Each plant was tied with
a rubber band in which a 2.5 cm long broom
stick was inserted to hold the inoculum
between the tillers.

The five assessment methods studied
are as follows:

Method 1: HRLH% (highest relative lesion
height) = (Highest lesion height/highest
plant height) x 100. This index is based on
the highest point reached by a sheath blight
lesion, relative to the highest point of the
plant, and is adapted form the Relative
Lesion Height method developed by Ahn et
al. (1986).

Method 2: DS% (disease severity)
Percentage of leaf or sheath area infected.
This is defined as the area of plant tissue
affected by disease expressed as a proportion
of total area (James and Teng, 1979). DS
was estimated by visual scoring of the top
three leaves and associated sheathhs.

Method 3: DI% (disease incidence)-
Percentage of infected tillers. This is defined
as the number of infected plant units,
expressed as a proportion of the total

January -June 1990

22 Philippine Phytopathology Vol. 2(
number of units assessed. DI (%) = [(No. of was calculated using the formula of Fr

IMuiu TCu usulg au iauoumiau iCaI area meici
(Li-cor, USA).

The intensity of sheathh blight was
assessed using each of the five methods; the
first assessment was done 3 days aftei
inoculation and subsequent assessments were
done weekly up to a maximum of 8 readings
Final recording was done at maturity,
Treatment means were calculated from five
observations in each replication for a
particular reading date in each cultivar.

Ine rice cultvar IKz 3Y-f86-2 had the
lowest AUDPC value (317.63) and highest
standard error (51.20) as compared to IR64
and IR72 in the case of disease severity (%)
(Table 1). The CV(%) was highest in
IR26957-86-2 (32.1%) followed by IR64
(15%) and IR72 (9.1%) based on AUDPC
for disease severity (Table 1). The disease
progress curve (Fig. 1) for DS showed that
IR64 and IR72 were small during all the
eight assessment times but these were high in
the case of IR26957-86-2 after 15 days of
inoculation (Fig. 1).

Method 4: SES- Standard evaluation system. inoculation at i th observation, and n = total
This system has been in use at IRRI and by number of observations. The AUDPCs had
cooperators in the worldwide International units of days-proportion and were used tc
Rice Testing Program (IRTP, 1980) since compare the five methods.
1980 and is based on a 6 level scale where 0
= no infection observed; 1 = lesions limited
to lower 1/4 of leaf sheaths; 3 = lesions RESULTS AND DISCUSSION
present on lower 1/2 of leaf sheaths;
5=lesions present on more than 1/2 of leaf For each variety and method ol
sheaths and slight infection is observed on assessment, approximately 8-9 assessments
lower leaves; 7 = lesions present on more were made to allow plotting of a disease
than 3/4 of leaf sheaths and severe infection progress curve (Fig. 1 and 2). We used
on upper leaves; and 9 = lesions reach top AUDPC as a criterion for comparison ol
of tillers and there is severe infection on all methods because of its integral nature.
leaves with some tillers killed.
The AUDPC based on % HRLH
Method 5: RAI% (real area infected) This presented in Table 1 showed that IR64 and
is the estimate of plant tissue affected by IR72 have higher AUDPC values than
disease expressed as a proportion of the total IR26957-86-2. The standard error values for
leaf of sheath area. This scoring system was the three cultivars were also high (29.0-
developed during the present study to 56.10), indicating that the method was
compare the other four scoring systems variable on the three cultivars. The
described above. The formula developed for coefficients of variation (CV%) based on
this method was, RAI% = 100 x (length x AUDPC showed that IR64 had lower CV%
width of lesion)/ [(length x width of leaf or (%) than the other two cultivars. The
sheath) x C.F.,] where C.F.= Correction difference in AUDPC between cultivars was
factor (0.67) for leaf and 0.83 for sheath). reflected in the disease progress curves (Fig.
The leaf correction factor was that of Gomez 1). The results showed that IR64 and IR72

January-June 1990 Assessment Methods 'for Rice Sheath Blight Disease

Sheathh blight assessment by disease
incidence (%) showed that all the three rice
cultivars had almost the same AUDPC value
(2068.13-2086.88 days-proportion) (Table 1).
Standard error was low in two cultivars
except IR72 where it was found to be higher
(12.25). The disease progress curve (Fig 1)
showed that disease incidence reached its
highest value (1005) at 6 days after
inoculation. The standard error at 3 days
after inoculation showed variability among
the three rice cultivars. Disease Incidence
therefore does not appear to have
discriminatory value in resistance screening
or to compare the progress of sheathh blight

The AUDPC values using the SES was
lowest among the different methods because
the scales range from 0 to 9. The AUDPC
values ranged from 68.55 to 90.60 days-
proportion among all the three rice cultivars
(Table 1). The standard error was also low
(5.20-9.60). The disease progress curve for
SES scale showed that cultivars IR64 and
IR72 had higher rates of disease increase
than IR26957-86-2 (Fig. 2). The standard
error value was almost similar and low in all
the cultivars at each assessment time.

The AUDPC for real area infected (%)
showed that IR26957-86-2 had the lowest
AUDPC value (294.67 days proportion) as
compared to the other two cultivars (Table
1). The standard error value varied among
the cultivars and the range was 10.01 to 24.22
(Table 1) and are comparatively higher than
SES and disease incidence. The disease
progress curve (Fig. 2) showed that cultivars
IR64 and IR72 had more disease than
IR26957-86-2. The standard error was higher
in cultivar IR64 than in IR72 and IR26957-

In the present study, all five assessment
methods that were evaluated for sheathh
blight disease were found to be variable with
different rice cultivars. This may be due to
different levels of resistance in the cultivars

or to variability associated with each method.
The results also showed that all assessment
methods had the lowest AUDPC value for
IR26957-86-2, a moderately resistant cultivar
compared with IR72 (highly susceptible) and
IR2 (susceptible). The assessment of
sheathh blight intensity using HRLH (%) is
dependent on individual tillers. It takes time
to measure each and every tiller in a hill;
however, the method is simple and easy to
use. According to Ahn et al (1986), ratings
of RLH (%) are easier and faster to use in a
uniformly inoculated mass screening nursery
than other methods.

In our studies, the visual estimation of
percent leaf and sheath area infected was
found to be faster than HRLH (%). It is
more efficient for evalating a large number rof
material within a limited time; however,
appropriate training to score the disease is
necessary because visual estimation may not
be accurate. This also confirms the results
found by other workers (Shane and Teng,
1984), although it is feasible to train
enumerators, using computer programs, to
improve their assessment abilities. The SES
was also found to be an easy and quick
method of assessment in the present study.
However, the human mind cannot assess
readily enough between 10 scale divisions (0-
9). Although three (1, 5, 9) or five (1, 3, 5, 7,
9) grades may be used, the ratings are
broadly spaced to be meaningful for
parametric or non-parametric statistical
analyses (Teng, 1987). Furthermore, the SES
scales were designed for screening of
resistance characteristics.

The use of real area infected was tried
as a standard method of assessment of
sheathh blight disease. While assessing the
real area infected some disadvantages were
encountered. These were (a) that the
method required detaching the leaf and
sheathh from the tiller, which ultimately
killed the plant before maturity, (b)
measurement of the length and width of
lesions was very tedious and only a few plants

January -June 1990

Assessment Methods for Rice Sheath Blight Disease

~miippino rnybopatnology Vol.26

would be necessary to modify this method so
that real area of infection may be assessed in
a simple and quick way. One possibility is
the use of video image analysis (Lindow and
Webb, 1983), which may become affordable
in the near future.

In selecting an assessment method for
epidemiological and yield loss studies, James
and Teng (1979) stipulated the criteria of
simplicity, reproducibility and ease-of-use.
Our study shows that either % HRLH or %
DS meet these criteria. Although Real Area
Infected is the most reliable because it
represents actual infected tissue, the cost of
labor and equipment to apply this method
makes it impractical for the large number of
samples in epidemiological studies. Disease
Incidence does not appear to be a suitable
method for sheathh blight assessment
because all tillers in a hill become infected
very soon after a primary source of infection
was established. While the SES is not suitable
for epidemiological or yield loss studies, it
nevertheless has value in screening for host
plant resistance.


new scale for rice sheath blight (ShB)
disease assessment. Intl. Rice Res.
Newsl. 11(6): 17.

FRY, W.E. 1978. Quantification of general
resistance of potato cultivars and
fungicide effects for integrated control
of potato late blight. Phytopathology 68:

GOMEZ, KA. 1972. Techniques for field
experiments with rice. International
Rice Research Institute, Los Bafios,
Laguna, Phil. 37 pp.

quanrmcauon o0 proaucuon constraints
associated with plant diseases. Applied
Biology (ed. T.H. Coaker) 4:201-267.

IRTP 1980. Standard Evaluation System for
Rice. International Rice Testing
Program. International Rice Research
Institute, Los Baiios, Laguna, Phil.

KOZAKA, T. 1975. Sheathh blight in rice
plants and its control. Rev. Pit. Protect.
Res. 8:69-79.

LINDOW, S.E. and R.R. WEBB. 1983.
Quantification of foliar plant disease
symptoms by microcomputer-digitized
video image analysis. Phytopathology

OU, S.H. 1985. Rice diseases,
Commonwealth Mycological Institute,
Kew, England 380 pp.

PARLEVLIET, J. E. 1979. Components of
resistance that reduce the rate of
epidemic development. Ann. Rev.
Phytopathol. 17:203-222.

TENG, P.S. 1975. A quantitative assessment
of padi foliar diseases in the Tanjong
Karang Irrigation Scheme, Selangor.
Malay. Agric'l. 50:78-99.

TENG, P.S. (Ed.). 1987. Crop Loss
Assessment and Pest Management.
American Phytopathological Society
Press. 270 pp.

TENG, P.S and SHANE, W.W. 1984.
Assessment of crop losses caused by
plant pathogens. Critical Reviews in
Plant Sciences 2:21-47.

'nulppine rnytopatnology

Vol. 26


It aui J.1. ri a uuui ui uJaaoI puIc Ua b
methods applied to three rice cul


HRLH (%) 861.86 bx + /29.00

DS (%) 437.81 cx +/-30.50

DI (%) 2086.88 ax + /-1.88

SES (0-9) 90.60 dc + /-5.20

RAI (%) 386.01 cx + /-24.22

CV(%) Cultivar 8.07

Mean of 4 replications

Means followed by a common letter in a colur
different at 5% level by DMRT

Figures within parenthesis indicate CV (%)

Vr aUU LaluaI u ~IU~Uor UL UV iLa, bssrcUlI
rs, measured in a greenhouse experiment,

IR72 IR26957-86-2

828.11 bx + /-56. 545.78 by + /-31.50
(13.5) (11.5)

424.88 cx + /-19.30 317.63 cy + /-51.20
(9.1) (32.1)

2068.13 ax+ /-12.25 2082.00 ax + /-6.36
(1.2) (0.6)

85.91 ex + /-7.95 68.55 dx + /-9.60
(17.6) (28.1)

347.29 dry + /-20.15 294.67 cy + /-10.01
11.6) (6.7)

Treatment 7.23

'a,b,c) or in a row (xy,z) are not significantly

Philippine Phytopathology Vol.26

Disease incidence (%)

3 6 9 12 15 18 21 24

5t- 70-
3 6 9 12 15 18 21 24 3 6 9 12 15 18 21 24

Days after inoculation
Figure 1. Disease progress curves based on Highest Relative Lesion Height (HRLH%), Disease
Severity (DS%) and Disease Incidence (DI%) for vertical sheath blight disease
development on three rice cultivars Each point is the mean of four assessments.
Vertical lines indicate standard errors.


Real area infected (%)

-, ..
3 6 9 12 15 18 21 24 3 6 9 12 15 18 21 24
Days after inoculation
Figure 2. Disease progress curves based on the Standard Evaluation System (SES) scales and Real
Area Infected (RAI%) for vertical sheath blight disease development on three rice
cultivars. Each point is the mean of four assessments. Vertical lines indicate standard

HRLH (%)

--I R72
- IR26957-86-2




I a I I I I I

Philippine Phytopathology

Vol. 26

1 QQf Phil- Phvtnnath 2A- 25-91


Marina P. Nati
and Mary Je

Respectively, Assistant Professor and :
Plant Pathology, College, of Agriculture, UP I


The etiology of a bacterial disea,
symptoms of the disease include leaf 1
observed more frequently. Systemically -
yellow orange followed by death of the w

Morphological, cultural, and physi
isolated from diseased plants was Xanti
anthurium isolate of X. c. dieffenba,
commutatum. A. amarantifolium. Aloci
oerstedi, Philodendron sp. (Emerald Ki
Philodendron x Mandaianum, P. micans,
Syngonium erythrophyllum, S. podophyllu&


Anthurium andreanum Lind is an or-
namental cultivated for its attractive flowers.
Popularly called anthurium, the flowers are
in demand in hotels, restaurants, and in
flower shops. It has a potential for export as
cutflower because the blooms are long-
lasting and resistant to bruises during hand-
ling and transport. Anthurium growing has,
thus, flourished from a hobby to a commer-
cial business enterprise.


Glenda A. Tabo
G. Telebanco

ter Undergraduate Students, Department of
Baiios, College, Laguna 4031, Philippines


f anthurium is hereby reported. Foliar
it and leaf spot with the former being
cted plants suddenly turn yellow green or

ical tests indicated that the bacterium
onas campestris pv. dieffenbachiae. The
was also pathogenic on Aglaonema
thibautiana, Dieffenbachia amoena, D.
Emerald Queen, Golden Erubescens),
pittiere P. panduriforme, P. squamiferum,
id Schizocasia lauterbachiana.

Expansion in production is, however,
threatened by a bacterial disease commonly
referred to as anthurium blight. The disease
was observed in the early 1980's
(Divinagracia, 1983). Leaf symptoms and the
bacterial nature of the disease were des-
cribed. Its significance was recognized only
recently when reports of epidemics were re-
ceived and verified. Interestingly, an outbreak
of anthurium blight was reported in the

and Fujiyama, 198"
the disease first ar

nost at the same time

ward in 1972 to occur in Kauai, Hawaii.

This study was conducted to describe
ptom variations which would be helpful
Irly detection and diagnosis of anthurium
it; to determine the etiology of the
ise, and identify potential alternate hosts
e pathogen.



Observations were made by the senior
or from naturally-infected plants in
houses around Los Bafios. Progress of
)tom development were observed in her

Isolation and Pathogenicity Test

Bacteria from advancing lesions of na-
ly infected leaves were streaked on
:o dextose peptone agar (PDPA) fol-
ag standard procedures. Yellow colonies
developed 72 hours after were sus-
ed in sterile distilled water and re-
ked on PDPA for purification.

Pathogenicity test was conducted by
ring a bacterial suspension (10 CFU
il) and spraying on pin-pricked leaves of
aguio White. Symptom development was
rved and the bacterium reisolated from
ted leaves. Control plants were provided
praying pin-pricked leaves with sterile
led water.


Identification of the isolate was based
athogenicity tests and studies of the

biological characteristics. The methods
were those described in the Society of
rican Bacteriologists' Manual of Mic-
ology Methods (1957), Fahy and
ward (1983) and Schaad (1988). Cultures
24-48 hour old in five replicates and in-
ted at 27-30 C. Speciation was based
arily on the descriptions of type species
e 8th edition of the Bergey's Manual of
rminative Bacteriology (1984). Compa-
is were made between the bacterium
-ibed by Hayward (1972) and McCulloch
Pirone (1939) and the anthurium blight

Alternate Hosts

Plant species belonging to the family
eae were collected around the Los
is area. Identification of the host was
i on Grafs' Exotic Plant Manual (1978),
ica (1981) and Exotica (1982).
dilation was conducted by infiltrating the
riall suspension (109 CFU per ml) in the
s using a hypodermic syringe.

A test plant was considered an alternate
of the bacterium if after inoculation,
toms developed and the bacterium
lated. Reinoculation to anthurium
d yield typical blight symptoms.



r Symptoms

The most common type of symptom
ved is leaf blight. The earliest
table manifestation of the disease is
ving of the leaf margin or wounded leaf
On the under surface of the leaf,
:e water-soaked spots about 1-2 mm in

_ 1_ __

IBIiIIht ofAtuIuI adeau

eter are evident. As the disease
essess, affected areas develop necrosis or
g-up of tissues. The enlarging, irregular
area is surrounded by a bright yellow,
soaked border (Fig. 1). This type of
tom has been observed on common
ars like Kaumana, Baguio White, Pink-
-dee, Nitta, Ozaki, Baguio Red, Exotica
Micky Mouse Red and Micky Mouse

Occasionally, leaf spots instead of leaf
s are observed. The lesions are
red over the entire leaf area and start
ddish brown spots with water-soaked
;rs and yellow halo. The spots later
ge and coalesce resulting in large
ed areas. As whole leaves become
tic, defoliation occurs. Petioles of
ed leaves are easily detached by pulling
from the main stem. Leaf spot has been
only observed in Baguio White
ngs but very seldom in the other

Systemic symptoms

[f blighted leaves are not removed at an
stage of infection, other leaves of the
plant that are apparently healthy will
orange to bright yellow. This is a
station that bacteria have been
nically-translocated from the infected
to the stem and other parts of the
Bacteria were found established in the
vessels by Sahai et al., (1990). Bacteria
bacterial products in the xylem prevent
location of water and mineral nutrients
leaves, thus the yellowing. The petioles
se systemically infected leaves break-off
y from the stem. The bases of petioles
re freshly-cut have distinct brown spots
in brown lines or streaks when the
e is cut lengthwise. This dark
orization corresponds to the infected
lar bundles in the petioles and can also
served in the stem and leaf veins. If the

.e is dipped in water, masses of bacteria
e seen oozing out from the cut portion.
:ually, the leaf sheaths, the newly
ging leaf and flower buds, or the entire
is killed.

The time interval from foliar infection
temic infection varies depending on the
)nment and the anthurium variety. It
observed that the disease became very
: in many shade houses around Los
During the summer of 1990 when light
;ity was unusually high and temperature
tbove 30 C. Alvarez et al. (1990) have
i that temperatures above 29.50C favor
plication of the bacterium. Nitta, Exotic
Micky Mouse Red and Orange were
nt to systemic infection but susceptible
lar blight. Baguio White and Kaumana

Blight of Anthurium andreanu


with rounded ends, gram-negative,

al Bfltaht oAntrhunum andrea

The bacterium was able to utilize' (Pammel) Smith; Pseudomonas
dextrose, fructose, sucrose, glucose, campestris (Pammel); Phytomonas
galactose, maltose, lactose, and campestris .(Pammel) Bergey et al.
arabinose oxidatively. The rate of Subjective synonyms: X. campestris var.
yellowing as the sign of acid production aberrans Vosel. and X. campestris var.
varied in all the sugars tested. Acid armoraceae (McCulloch) Starr and
production was first observed in maltose Burkholder]. Its distiguishing
and then on sucrose, 4 and 5 days after characteristics are: ability to a) liquefy
inoculation, respectively. Acid gelatin, b) milk peptonization with no
production was slow in lactose, fructose, acd or curd (only X. campestris exhibit
and glucose which was observed 6 days milk proteolysis.) Other species namely
after inoculation. However, fast X. ampelina, X. axonopodis, X. fragarias
production of acid was detected in and X. albilineans are negative to mild
dextrose. In contrast, acid was not proteolysis, c) produce hydrogen sulfide,
produced in glycerol and mannitol even d) hydrolyze aesculin, e) produced
after three weeks of inoculation, mucoid growth on nutrient agar plus 5%
glucose, and f) produce acid from
The thermal death point of the glucose, dextrose, galactose, sucrose,
bacterium was recorded at 51 C since lactose, arabinose, and fructose, g)
one or two colonies or none at all was inability to reduce nitrate to nitrite and
found in the plates. No growth was inability to produce urease.
observed at 55 C and 60 C. Hydrogen
sulfide was detected 2 days after The characteristics of the leaf
growing the bacteria in peptone water. blight bacterium under study are very
Catalase production was very strong. similar to Xanthomonas dieffenbachiae,
Starch, Tween 80, gelatin (after 9 days), first described by McCulloch & Pirone
and aesculin were hydrolyzed. There (Dowson), in cultural, morphological,
was a slow clearing of litmus milk but and physiological characters (Table 2).
acid nor curd was not formed. Nitrates Following the new system of naming
were not reduced to nitrites. Voges bacteria (Skerman et al., 1980), the
Proskauer test to detect acetyl anthurium blight pathogen is named
methylcarbinol, indole test and urease Xanthomonas campestris pv.
were negative. No capsules were dieffenbachiae. Although there are more
detectable from negatively stained cells similarities, few differences can also be
using India ink from culture grown in observed. The bacterium under study
high sugar medium (Table 3). measures 0.4-0.8 x 1.0-2.0 u and did not
form capsules. It did not produced acid
The characteristics of the from glycerol but produce acid from
bacterium under study are typical of the maltose. In contrast, X. dieffenbachiae
genus Xanthomonas as described in the formed capsules and is small (0.3-0.4 x
Bergey's Manual of Systematic 1.0-1.5 u). It produces acid from
Bacteriology (1984).The cultural,. glycerol and does not produce acid from
morphological, and physiological maltose. The leaf spot bacterium
characteristics of the leaf blight reported by Hayward (1972) was also
bacterium listed in Table 3 are very similar to the bacterium under study,
similar to Xanthomonas campestris however, few differences are noticeable.

(Pammel): Bacterium


30 Philippine Phytopathology Vol. 26

from glycerol and mannitol. Except for was observed. Inoculation were
the differences stated above, all other repeated three times.
characters are the same for the three
bacteria. Naturally-infected Aglaonema sp.,
Syngonium sp., Dieffenbachia sp. and
Alternate Host ofX. c. pv. Philodendron sp. had been reported b3
diefffenbachiae various authors (Wehlburg, 1968,
McCulloch and Pirone, 1939:
Artificial inoculations conducted McFadden, 1967 and 1962; Chase, 1987:
by infiltrating leaves with about 10 Dickey and Zumoff, 1987). In the
CFU per ml identified plant species that Philippines, no X.c. pv. dieffenbachiae
could be infected by X. c. pv. had yet been isolated from these hosts
dieffenbachiae. These plants allowed the although these plants had beer
multiplication of bacteria. The lesions observed to show the disease. It would
enlarged until the entire leaves were be interesting to know if bacteria from
blighted and later fell off. Bacteria these hosts would cross-infecl
isolated from these hosts were anthuriums. Control of anthurium blight
reisolated and confirmed to be X. c. should include eradication of alternate
dieffenbachiae. Considered as alternate hosts as potential sources of inoculum.
hosts after inoculation are Aglaonema
commutatum. A. marantifolium.
Alocasia thibautiana. Dieffenbachia
amoena, D. oerstedii, Philodendron
(Emerald King), Philodendron
(Emetald Queen), Philodendron
(Golden Erubescens), Philodendron x

syngonium erytnropnytuum, Nyngonmum
podophyllum, Schizocasia
lauterbachiana (Table 3).

Watersoaking of the leaf under
surface 3-4 days after inoculation was
the most common reaction of the
different hosts. A few days later, the
watersoaked area turned yellow to
orange brown. This would later become
necrotic. After 2-3 weeks the infiltrated
leaves dried-up due to coalescing
lesions. Systemic infections were not
observed on these plants which were
kept 2 months after inoculation. No
disease was produced on P. selloum, P.
wendlandii, Philodendron (variegated),
Philodendron (Majesty) and Alocasia
indica metallic. The infiltered area
dried-up and a hypersensitive reaction

i 7.

ure 3. Plants artificially inoculated with Xanthomona.
Symptoms were reproduced on a) A. andreant



~_. ;=.'.
t' _m^

32 Pfnlappine fnylopamoiogy Vol. 21

Table 1. Colony characteristics of the leaf blight bacterium of anthurium on various media

Media Colony Characteristics

PDPA colonies were yellow orange, smooth, circular, entire, raise<
glistening. The colonies were 1-2 mm in diam. 5 days afte

akimoto's agar colonies were pale yellow, circular, raised, smooth, entire, an<
glistening, 1-2 mm in diam. 5 days after inoculation.

King's medium B colonies yellow with circular, smooth, entire margin, glistening,
mm in diam. 5 days after inoculation.

Tetrazolium colonies red surrounded by narrow white entire, smooth, circular
viscid, glistening, 1-2 mm in diam. 5 days after inoculation.

YDCO colonies were yellow orange, smooth, punctiform, entire, raised
glistening, 0.5 mm in diam. 5 days after inoculation.

Nutrient agar colonies similar to KMB. yellow, punctiform to circular, white entire
smooth margin, convex, and glistening, 0.5-1.0 mm in diam. 1
days after inoculation.

January June 1990 Bacterial Blight of Anthurium andreanum 33

Table 2. Cultural, morphological, and physiological coniparisons of Xanthomonas
dieffenbachiae(McCulloch and Pirone) Dowson. Hawaii isolate and Laguna isolate.

X dieffenbachia sp. Hawaii isolate
Specification (McCulloch and Pirone)(Hayward, 1972) Laguna isolate

Host and general Dieffenbachia sp. Anthurium andreanum cv Anthurium endreat
effects Dracaeba fragcabs Kansako Red. W1

Leaf spot on the Philodendron oxycardium sudden death of la
hosts Dieffenbachia picta leaf areas
angular pale brown
necrotic spots with
yellow chloride halo

Morphology straight rods gram negative rods straight rods, 0.4-
0.3-04 x 0.8 xl.0-2.0 u
1.5 u, gram single or in pairs,
negative, single gram, negative, sir
or in pairs, single

Colonies on NA or plae yellow to yellow viscid growth deep yellow, punti

entIre, circular,
flat, smooth,
butyrous to slightly
viscid in older

'apsule formation formed

'elatin, starch hydrolyzed
'ween 80

,itmus milk slow peptoni-
zation, tyrosine

icid reaction acid from
glucose, sucrose,
fructose, lactose
glycerol. No acid
from maltose or

T* ... 1 .. _


lata capsules not former

rolyzed hydrolyzed

lata slow clearing by
proteolyctic action
with no acid or cure

I from dextrose acid from arabinose
those galactose, sucros, lactose
:ose, glycerol, maltose, galactose
ose, maltose dextrose, fructose,
n maltose or mannitol.
anitol. arabinose. No acid
from glycerol and

34 Philippine Phytopathology

Table Z. oonunuea

X dieffenbachia sp.
Specification (McCulloch and Piroi

Indole no indole

H2S production H2S produced no data

Relation to oxygen
aerobic aerobic

Aesculin no data

Catalase positive

Table 3. Pathogenicity of Anthurium is
species belonging to family Arao


Anthurium andreanum
Aglaonema commutatum
Aglaonema marantifolium
Alocasia indica metallica
Alocasia thibautiana
Dieffenbachia amoena
Dieffenbachia oerstedii
Philodendron (Emeral King)
Philodendron (Emeral Queen)
Philodendron (Golden Erubescens)
Philodendron (Majesty)
Philodendron x mandaianum
Philodendron micans
Philodendron panduriforme
Philodendron pittiere
Philodendron selloum
Philodendron squamiferum
Philodendron (Variegated)
Philodendron wendlandii
Syngonium erythrophyllum
Syngonium podophyllum
Schizocasia lauterbachiana

Legend; (+) infected; (-) not infected

Hawaii isolate
(Hayward, 1972) Laguna isolate

no data no indole

H2S produced


hydrolyzed hydrolyzed

positive positive

:e of X.c. dieffenbachia in different plant







Philippnine Phytopatholoav


---...-, - Tacierilal DIgni or fIIILnmunum wuruaniuiII a

Bacterial leaf spot of Dieffenbachia
ALVAREZ, A., R. LIPP, D. NORMAN and Phytopathology 29: 956-962.
L. GLADSTONE. 1990. Epidemiology
and control of Anthurium blight. McFADDEN, LA. 1962. Two bacteria
Proceedings of the Third Anthurium pathogens affecting leaves o
Blight Conference held May 12-14, Aglaonema robelinii. Phytopatholog
1990, UH at Hilo, Hawaii. 52:20.

CHASE, A.R. 1987. Leaf spot and blight of McFADDEN, LA. 1967. A Xanthomona
Strelitzia reginae (bird-of-paradise) infection of Philodendron oxycardiun
caused by Xanthomonas campestris. leaves. (Abst.). Phytopathology 57:343.
Plant Dis Rept. 71:845-847.
McFADDEN, LA. 1962. The bacteria
DICKEY, S.D. and C.H. ZUMOFF. 1987. pathogens affecting leaves o
Bacterial leaf blight of Syngonium Aglaonema robelinii. Phytopatholog
caused by a pathovar of Xanthomonas 52:20.
campestris. Phytopathology 7:1257-1262.
DIVINAGRACIA, G.G. 1983. Diseases of 1985. Bacterial blight of anthurium
important foliage and flowering Hawaii Cooperative Extension Service
ornamental plants. Terminal Rept. Hawaii Institute of Tropical Agricultun
UPLB p. 9. and Human Resources. University o
Hawaii and Manoa. Community Fac
FAHY, P.C. and A.C. HAYWARD. 1983. Sheet AN- 4 (a). pp. 1-3.
Media and methods for isolation and
diagnostic tests. pp. 337-374. In FAHY, ROBBS, C.F. 1960. Bacteria:
P.C. and GJ. PERSLEY. 1983. Plant fitopathogenicas no Brassi
Bacterial Diseases: A Diagnostic Guide. (Phytopathogenic bacteria in Brazil)
Acad. Press. Autrialia. 393 p. Inst. Econ. Rural, Rio de J. Ser. Divulg
Pesq., 2. 63 p.
GRAF, A.B. 1978. Exotic plant manual. (5th

Phil. Phytopathological Society, Inc.
1990 Phil. Phytopath 26: 36-41



Assistant Professor and Science Research Assistant, Philippine Root Crop Research and
Training Center (PRCRTC) Baybay, Leyte, Philippines.


Eight isolates of Sphaceloma batatas were obtained from stem and
foliage samples of sweet potato collected from Baybay and Abuyog, Leyte.
The differential cultivars, IVSP2, VSPy G145r4, BNAS51, V3.158 and CI69,-9'
were inoculated with spore suspension from each isolate two weeks after
planting, then evaluated for disease reaction 16 days later. The data obtained
showed that S. batatas isolates varied in their ability to incite disease as
reflected in the variation in relative number of lesions produced and the
differential reactions of the host varieties. Of the eight isolates tested, the
most virulent isolate was PRS182 followed by V11-148 with respective mean
lesion density of 43.78 and 38.45. Isolates V1.P.. 0145r-4Q PRS 87, V3-153.
BNAS51,, and V11_39, were found least virulent with mean lesion densities of
27.7 23.2, 23.2, 22.5, 22.1 and 21.2, respectively.

INTRODUCTION Due to the potential damage of this
disease, researchers geared their interest to
The need to stabilize sweet potato yield study culture, morphology, pathogenicity,
has spurred large scale movement of infectivity and the in-vitro production of the
breeding materials. However, the scab pathogen (Lao and Divinagracia, 1979;
accelerated pace of planting material Bajit and Gapasin, 1987; Paningbatan, 1987).
exchange has increased the risk of spreading Attempts to control the disease have
crop pests and diseases. been primarily through chemicals
-. * i r. 1* I /w.y^ . *_ 11 'k __ .. .. 1 *f\lp\l' .., ._ 3

Sphaceloma batatas Saw is presently a breeding

ana rmsea tnree times m sterile alstllea
water. Suspension was then plated on Water
MATERIALS AND METHODS agar (WA) either acidified with lactic acid or
added with streptomycin Pure cultures
Survey, field observations and obtained were transferred to malt extract
evaluation of the reaction of different sweet agar (MEA) slants with chloramphenicol and
potato genotypes to scab. kept in suitable temperature. Bimonthly
transfers of the isolates to MEA slants were
The PRCRTC sweet potato germplasm done to ensure sufficient source of inoculum.
collection and 101 other sweet potato
genotypes grown in different experimental Selection of differential hosts for pathogenic
fields at Pangasugan and ViSCA, Baybay, variation
Leyte and Abuyog Experimental Station
(AES), Abuyog Leyte were surveyed for the The differential hosts for studying the
occurrence of scab and rated for severity of pathogenicity of S. batatas were VSP2,
the disease. Evaluation, based on the density G145r-4, BNAS 51, V3-158 and CI-693-9.
of lesions on the infected plant parts, used These varieties were chosen based on their
the disease rating scale described below: distinct reactions to scab as observed by
Gapasin and Esguerra (1984) and in the
preliminary evaluation of sweet potato
RATING SCALE genotypes. Varieties VSP 2 and VSP 3 and
lines V3-158 have been found to be resistant,
Scale Description moderately resistant and highly susceptible,
Reaction respectively. Genotypes, G145r-4 BNAS 51
and CI-693-9, were added in order to have a

38 Philippine Phytopathology Vol. 26

sid using the randomized completely block type of reactions developed in the
design (RCBD) with three replications. differential host varieties. As shown in Table
Disease performance on the differential 2, four reaction types were observed among
lost was evaluated 16 days after incoluation the 6 host varieties infected by isolates, V11
Rising the rating scale previously described. 398* Resistant reactions were noted on VSP2
and CI939, moderately resistant on VSP,
susceptible on G145r-4 and highly susceptible
RESULTS AND DISCUSSION on BNAS51 and V .158 Isolates V11398 and
V 315 could therefore be differentiated from
characteristicc symptoms on differential isolates PRS87 and G145r4 by the highly
losts susceptible reaction of VSP3 and moderately
resistant reaction of G 45-r4 to the latter
Sixteen days after inoculation with the isolates. On the other hand, isolates V 148'
ight scab isolates, visual observation of V-253 and PRSg82 could be identified from
symptoms on the differential hosts revealed isolates V1-398 and V3.15 by the highly
differences in lesion size, shape and color. susceptible reaction'of VSP3 and CI 9,.
'he shape of the lesions were irregularly With isolate BNAS51, it is differentiated
leptical to elongate, while others were oval from isolates V 1139 and V-158 by the
o spherical. Young lesions were mostly moderately resistant reaction of G145r-4'
longate and became irregular and tended to Among the differential hosts, VSP2
oalesces as they matured. Furthermore, consistently showed a resistant reaction to
esions were whitish to pale brown with infection by all the S. batatas isolates while
eddish margins on the leaves and petioles of BNAS51 and V3-158 consistently showed
he test plants 5 to 7 days after inoculation. highly susceptible type of reaction to
'hey turned dark brown, maroon or reddish infection by all eight isolates. All the others
irown at the later stage of development. have two kinds of reaction.
Data obtained indicate that the S.
comparisonn on scab lesion density and batatas isolates tested varied in virulence.
action of differential hosts The differential hosts utilized made possible
the demonstration of these differences in
Table 1 shows the lesion density per 30 virulence among the isolates. The most

he highest number of mean diesiiies of 43.9 found leasYt virulent. -These observi

lone in the presence of the variants of the
)athogen at different seasons and locations. NAYGA, J.C. and R.,M. GAPASIN. 1986.
Studies of the pathogenic variation of S. Effect of stem and foliage scab disease
>atatas is relatively new. There are still many on the growth and yield of VSP 1, sweet
elevant areas that need to elucidated before potato variety. Ann. Trop. Res. 8(3)
i conclusive means of identifying strains 115-122.
md/or races of the Dathoeen can be done.

solate and a standard set of differential hosts
are identified including genes for virulence in
he fungal population and the corresponding
;enes for resistance in the hosts, these races
:an ascertained.


WAJIT, G.B. and R.M. GAPASIN. 1987.
Relationship between morphological
characteristics and varietal resistance of
sweet potato to scab infection caused by
Sphaceloma batatas Saw. Ann. Trop,
Res. 9 (20); 75-83.

3ANIQUED, CA. 1986. Sweet potato
diseases and their control. In State of
the Art Sweet Potato Research. Crop
Research Series No. 9. PRIS pp. 25-29.

MAILUM. 1975. Sweet potato
(Ipomoea batatae) stem and foliage
scab, Sphaceloma batatas; Fungicide
and Nematicide test results. Amer.
Phytophatology Soc. 31:104.

1984. Studies on diseases of sweet
potato with emphasis on sweet potato
scab. In Research Highlights for the
Bafios, Laguna p. 59.

1979. Culture of the sweet potato scab
fungus (Sphacelomalbatatas Saw). Ann.
Trop. Res. 1(1) 1-13.

r~YI~IYLD~I/vi nm. IYZII. IniecuiviIy
and in vitro production of sweet potato
scab fungus (Sphaceloma batatas).
Ann. Trop. Res. 9(1)24-33.

40 IllIppIn. Phytopatho

Differential ISOLATES
V11-398 V3-158 PRS387

VSP2 7.3 8.3 2.0

VSP3 16.0 17.0 45.7

G145r-4 28.3 23.0 19.7 1

BNAS51 34.0 40.7 45.7

V3-158 38.3 41.0 25.7

CI693-9 3.0 5.0 0.7

Mean 21.2c 22.5bc 23.2bc

J/ Means of three replications, results of two trials. I
level based on Duncan's Multiple Range test (DMI

15r-4 V11-148 V11-253PRS182 BNAS51

4.3 3.0 6.0 7.7

32.0 32.0 45.7 18.3

23.3 24.7 25.3 18.7

33.0 34.3 36.7 33.0

48.0 35.7 78.0 54.0

90.0 36.7 71.0 0.7

be 38.5ab 27.7bc 43.8a 22.1bc

is with the same letter are not significantly different at 59


uinppine Phytopatho

Pathogenic Variation of Soh

V11-398 V3-158 PRS387 G145r-4



3145r-4 S S MR MR


V3-158 HS HS HS HS

CI693-9 R R R R

J/ Reaction categories used:

HR = Highly resistant (no symptom on

R = Resistant (occasional lesions on

MR = Moderately resistant (scattered
cm of vine)

S = Susceptible (more than 20 lesion

HS = Highly susceptible (numerous 1


1-148 V11-253 PRS182 BNAS51







f and stem)

er stem or leaf, 10 lesions per 30 cm of vine)

ans on stem and leaves, 11-20 lesions per 30

:r 30 cm. of vine slight leaf deformation)

ins on both leaf and stem with severe leaf

-'--I --~~--- -- --- - Z:


Phil. Phvtopatholo(

1990 Phil. Phvtopath 26: 42-29

lsurK., IVICr. 1
Belly T. Dionio

Supported in part by the Philippine I
Research and Development (PCARRD), Los
Respectively, Assistant Professor, Depa
University of Southern Mindanao, Kabacan,
Plant Pathology, College of Agriculture, Ur
Laguna, Philippines.

Fourteen isolates of Erwinia chry,
causal pathogen of bacterial stalk re
in Central and Southern Mindana
percent infection and percent topp
infection 75.9 and percent toppling
days with isolate E2 but infection b,
after inoculation. Differences in i
likewise noted. Considerable degree
cultivars. Both hybrids and open-po
for resistance that can be acc


Bacterial stalk rot caused by Erwini
chrysanthemi Burk., McFad and Dimock i
one of the most important disease associate
with corn production in the Philippines. Th
disease, first observed and reported b
Dalmacio and Exconde (1970) appears to b
more prevalent in areas with poor drainage
and where recommended hybrids or varieties
are grown. Surveys conducted from 1982
1989 showed a steady increase in th
occurrence of bacterial stalk rot in the corn
growing provinces of North, and Sout
Cotabato, Sultan Kudarat, Davao province
Bukidnon, Negros Occidental and Leyt
(Raymundo and Dionio, 1989). Stalk rc
disease is characterized by rotting of the stal
which usually starts from the bas
progressing upward and eventually causing
the leaves to wither. Infected plants eith<
topple over or remain standing until maturity

1K1VVYII 1. ri I I3l1N irlrvii
Dim. in CORN
I A.D. Raymundo

ncil for Agriculture, Forestry and Resources
fios, Laguna, Philippines.
ent of Plant Pathology, College of Agriculture
tabato and Assistant Professor, Department ol
:sity of the Philippines at Los Bafios, College


hemi Burk., Burk., McF. & Dim., the
f corn, collected from various localities
iere tested for variability in terms of
on Pioneer 3208. The highest percent
42.0 were obtained with isolate D1 6
any isolates were observed only 40 days
action rates and rate of lodging were
f resistance was found in a number of
ited varieties appeared to possess genes
dated through appropriate selection

adverse conditions by infecting weed specie
that are common in corn fields and in the so
for extended periods of time encompassing
several growing seasons.

Knowledge on pathogenic variability c
E. chrysanthemi in the field is essential in th
development of cultivars resistant to bacteria;
stalk rot. Pathogenic races or biotypes ca
occur by mutation and subsequent adaptatio
with possible changes in virulence may alter
the reaction of many resistant varieties c
hybrids. Likewise, the identification (
materials resistant to the disease is
prerequisite to the formation of population
and eventually resistant cultivars.


Collection and Isolation of the Test Isolates

I..- %'a r . w. *

,na.,. A Oe.a.ak VU.I 5.

laced in separate plastic bags and labelled
properly. The bacterium isolated from
ifected corn tissues was cultured using
otato dextrose peptone agar (PDPA).
noculum preparation and Inoculation of
. chrysanthemi Isolates
Inoculum suspension from 48 hr old
ure cultures was prepared by adding 8-10 ml
f distilled water to each test tube slant and
raping the colonies using a sterilized glass
ad. The inoculum density was standardized
sing Spectronic 20 at 50% transmittance and
25 wave-length. Inoculation was done on
ve week old corn plants (Pioneer 3208) by
dropping 2 ml of the bacterial Buspension
ito the whorl of the plants.
)ata Gathered
Various parameters obtained to
determine variation in'the aggressiveness and
irulence of E. chrysanthemi isolates included
1) incubation period and length of time for
first symptom to appear (2) percent infection,
3) percent toppling, (4) rate of disease
'valuation of the reaction of corn hybrids and
varieties to bacterial stalk rot
Most of the materials evaluated for
action to bacterial stalk rot were hybrids
nd varieties recommended for inclusion in
ie national corn program. The entries
lanteu in 5 m long rows and were artificially
loculated twice: at one month after planting
sing the whorl method and at early
isselling stage by the nail puncture method.
L 2-day-old pure culture of the bacterium,
tandardized at 50% transmittance (425 nm)
rith a spectrophotometer, was utilized

'athogenic variability ofE. chrysanthemi
The 14 isolates differed significantly in
nset of infection, percent infection, percent
)ppling, rate of disease development ana

. .----- --. .- -. -. --.- . . . '
ifter inoculation with Isolate E2 while most
)f the isolated produced symptoms about 40
lays after inoculation. Isolate C elicited the
ongest incubation period of 50 days.

The highest percentage infection of 75.9
md percent lodging of 42.0 were likewise
obtainedd with isolate D1. Isolate E2 caused
i7.5% infection and 12.5% toppling. Other
solates had percentage infection ranging
rom 36 to 62 and percent lodging of 0 to 5.0.

Isolates B1, B2, D2, D4, and F1 did not
cause toppling of plants (Table 1). This can
)e attributed to the late onset of the disease
lue to most isolates.

Isolate D1 caused the fastest rate of
disease increase of 0.021 and rate of lodging
>f 0.00642. Isolate E2, on the other hand,
;ave r-value of 0.014 and rate of toppling
).00175. The rest of the isolates had r-values
-anging from 0.006 to 0.016 and toppling rate
)f 0 to 0.000856 (Table 1).

Of the 14 isolates, Isolate D1 was
considered to be the most virulent followed
by Isolate E2. It can be noted that isolates
-esponsible for earlier onset of the disease
also incited the highest percentage infection
md toppling of plants (Table 1).
Consequently, rate of disease development
md rate of toppling were faster with these
solates (Figs. 1 and 2).

Among the criteria used to determine
variation among isolates, onset of infection
appears to be the key parameter.
Results of this study show the variation
n terms of virulence and aggressiveness exists
imong isolates of E. chrysanthemi inoculated
mder field conditio.A Previous works by
garibaldi and Bateman (1973) showed
differences in the amount of '.llulolytic and
proteolytic enzyme produced by E.
*hrysanthemi isolates. Further studies by. the


44Phlppn Phytopat

variaLton m virulence among Isuiats. m11
the most virulent isolate produces the large
number of isozymes while the least virule
isolate produces the smallest amount

Host Resistance to E. chrysanthemi

A two-year trial showed a range
reaction of corn cultivars to E. chrysanthen
Highest percentages of infection wre 20.7
1988, and 20.5 in 1989 (Table 2 and 3).
1988, hybrid, P82960 sustained the high(
percent infection.

Considerable degree of resistance c
be found in IPB varieties 2 and 4 as well as
SMARC 1887, IES Var. 7, SMC hybri(
SMC-E19, SMC 308, and SMC-E9; CG54
and in P82943, P8401 and P61528.

Percent stalk rot infection inf the 19.
trial was highest in IPB Var. 1 with a mean
20.5 while the lowest was in P3208 with 1
percent (Table 4.). Some hybrids, name
YCPG 83, CS8820, CS8818, 77709, SMC 3
and YCPG 81 showed resistance to t]
pathogen. The last two hybrids were
resistant as P3208.

Although the trials were bothered 1
dry weather, especially during the eaj
stages of disease development, the result
showed considerable differences in resistan
among entries. It is possible to select fro
among all cultivars, many of which a
already recommended for commerce
cultivation, the variety or hybrid suitable
area where incidence of the disease is high.

1970. Diseases of corn unreported in tl
Philippines. Phil. Phytopathol. 6:90-97.

1973. Pectolytic, cellulolytic aj
proteolytic enzymes produced by isola
of E. chrysanthemi Burk., McFad. ai
Dimock. Phytopathol. Mediterr. 12:3

1978. Pectic enzymes produced by I
chrysanthemi and their effects in plar
tissue. Physiol. Plant Pathol. 11:25-40.

1989. Epidemiology and host resistance
to bacterial stalk rot of corn. Annu;
Report. Philippine Council f(
Agriculture, Forestry and Resourca
Research and Development, Lo,
Baiios, Laguna 51 pp.


Philippine Phytopatt

January June 1990 No. 1 & 2 Components of Pathogenic Variability 45

Table 1. Incubation period (DAI), % infection, % toppling, apparent infection rate, and of
lodging caused by 14 isolates of Erwinia chrysanthemi on Pioneer 3208.



54.5 abcd
47.5 bcd
62.5 ab
49.1 bcd
37.5 cd
59.3 abc
42.5 bcd
.48.5 bed
57.5 abcd
62.9 ab


2.5 bc

12.5 b
2.5 bc
2.1 be



CV = 9.75% CV 29.05%
A2 USM (main campus)
B Tondo, Carmen, N. Cotabato
B Tawan-tawan, Carmen, N. Cotabato
C Pioneer Overseas Corporation, General Santos City
D Malipayon, Koronadal, S. Cotabato
D2 Katipunan, Koronadal, S. Cotabato
D3 Luna, Koronadal, S. Cotabato
D4 Bo. 7, Koronadal, S. Cotabato
S- Bo. 2, Banga, S. Cotabato
F Bo. 6,Banga S. Cotabato
F Tupi, S. Cotabato
G Surallah, S. Cotabato
H Polomolok, S. Cotabato
d DAI Days after inoculation

CAverage of four replications. Means within a column followed by a common letter are not significantly different at
1% level.

d Calculated based on mean percentage infection taken at 2-day intervals starting from days after inoculation until
near maturity.

e Calculated based on mean percentage lodging taken at 5-day-intervals.

A pp y p gy J .

ill ine Ph to atholo

lo -1


[PB Var. 1
IPB Var. 2
DK 887
SMC 308
SMC E 21
CS 8820
CS 8818
SMC 318
P 3208

Average of four replications. Means fofll
different at 1% level.


20.5 a
17.9 a
13.8 a
13.6 a
13.3 a
12.9 a
11.9 ab
11.0 ab
9.0 ab
6.9 ab
4.2 b
3.2 b
1.5 b
1.5 b
1.4 b

Ad by a common letter are not significantly


SMC 317
P 3228
CPX 622
CPX 721
P 3274
VISCA 8311
IES Var. 2
IPB Var 1
F 61527
F 3224
CPX 623
Visca 8426
Visca 8346
IES Var 7
SMC- E19
P 82943
P 8401
SMC 308
CG 5401
IPB Var. 4
SMARC 1887
CPX 621
IPB Var. 2
P 61528

SMeans with common letter are not significa


20.7 a
18.4 ab
17.3 abc
16.6 abc
16.3 abc
15.8 abc
14.9 abc
14.1 abc
13.8 abc
13.6 abc
12.4 abc
12.3 abc
11.0 abc
11.0 abc
10.9 abc
9.4 abc
8.6 abc
7.6 abc
7.6 abc
6.9 abc
6.4 abc
6.3 abc
5.4 be
5.4 bc
4.8 bc
4.2 bc
3.8 bc
2.8 c



Z 20

2 4 6 8 10 12 14

Figure 1 Disease progr

M-- --*-*-*-*-- --

S18 20) 22 24 26 28 30 32 34 36 38 4(
Time (days after Inoculation)

Sdue to 14 isolates of Erwinia chrysanthemi ii

51 I

January June 1990 No. 1 & 2 Components of Pathoaenic Variability 49

0 -- 0- IsolateD1

x -- x Isolate E2
0 0 Isolate D
A A Isolate F,G

11 -- I Isolate A2

S-- C- Isolate C
A -- A- Isolate H
S-- Isolate A1, B2, B2, D2, D4, E1




' 25




5 x

5 10 15 20) 25 30 35
Time (Days after Inoculatior

Fig. 2 Progress curves for toppling due to 14 i


- t *- at F-a C F, G, A2
E--I 0-- ; A1, B1, B2, D2, D4, E1
45 50 55 60

ates of Erwinia chrysanthemini in corn.


Abstracts of papers presented during tt
Pest Control Council of the Philippines held
10, 1990.

Onset of Single Infection with Either Rice
Tungro Bacilliform Virus (RTBV) or Rice
Tungro Spherical Virus (RTSV) and Its
Transition to Composite Infection. E. R
Tiongco, Z. M. Flores, R. C. Cabunagan, H.
Hibino, & H. Koganezawa. International
Rice Research Institute (IRRI) and National
Agriculture Research Center, Japan.

Level of tungro infection was low ii
seedling wetbed nursery and considerable3
increased after transplanting.

The transition from healthy tc
composite infection of plants with RTBV anc
RTSV was monitored by ELISA. RTSV wa:
detected during the second and third week!
during which tungro symptoms became
apparent. Four weeks after transplanting
composite infection was observed mostly ir
previously healthy plants and in few plant!
previously infected with either RTBV oi
RTSV. By the fifth week after transplanting
most of the remaining healthy and previously
RTSV-infected plants became double;
infected. This indicates that composite
infection does not necessarily result fron
single infection with either RTBV or RTSV.

The first few weeks after transplanting
were critical for tungro development. The us
of insecticides at the early growth stage o
transplanted rice showed the progress of the
disease in the susceptible cultivar. Th<
development of tungro in the RTSV-resistan
cultivar was considerably reduced evei
without the use of insecticides.

Effect of Temperature and Humidity oi
Germination and Infection o
Collectotrichum gloesporioides (Penz.) Sacc
on 'Carabao' Mango (Mangifera indica L.)
A. B. Estrada, & L. L. Ilag. University of the
Philippines at Los Banos (UPLB)

Experiments were conducted t4
evaluate the effect of temperature anm


11st Anniversary and Annual Convention of the
the Sugarland Hotel, Bacolod City from May 7-

growth of the anthracnose fungus. Results ol
these experiments together with actual field
weather data were used to evaluate the
worthiness of the scheduled spray program
employed in a mango orchard in Dasmarinas

Germination and growth of C
gloeosproioides were found highly sensitive tc
temperature and atmospheric humidity. The
optimum temperature range for germ tube
formation and growth was from 25 to 30 C
Spore germination and fungal growth
increased as the RH was increased from 9(
to 100% with profuse growth observed ai
97.5 and 100%7o RH. Germination on glass
slides was inhibited at RHs 90% and belov
even after incubation at 30 C for 36 hr. A
higher germination percentage and more
profuse growth were observed on leaves anc
fruit peels than on glass slides. There was n(
relationship between the stage of frui
development and germination, mycelia
growth and appressorial formation.

Appresorial formation increased witl
increasing, temperature and humidity. N(
appressoria were formed at 90% RE
irrespective of the temperature of incubation
Very few were formed at 2( C even after 38 1
of incubation at 100% RH. Less appressoriu
were observed on peels than on leaves. N(
appressoria were formed on glass slides
Increased appressorial formation resulted ii
increased severity of anthracnose infection ii
mango leaves. Lesions appeared earlier an<
were more severe under 97.5 and 100% RI
at 25 and 30 C.

Evaluation of the standard spra:
program revealed that majority of the
scheduled fungicide sprays in the program
were made during low anthracnose-risl

Effect of Xanthomonas campestris pv. oryza,
Infection on the Dry Matter and Chloronhvl

January-June 1990 Abstract of PaDers

Content of Rice. J. F. Bai, R. P. Robles, & T.
W. Mew. IRRI and UPLB.

Physiological disorders of rice plant due
to Xanthomonas campestris pv. oryzae (Xco)
infection were studied using a compatible
rice-Xco combination involving six inoculum
density levels. Amount of dry matter
correlated with photosynthetic leaf area.
Phytomass, totaL plant dry weight and
photosynthetic leaf area were negatively
correlated with disease severity. The slopes
(X-coefficients) and r values (correlation
coefficients) of disease severity with respect
to the above-mentioned parameters
increased weeks after inoculation indicating
that disease severity influenced plant growth.
Initial inoculum density was important in
disease development. Increased leaf-weight
ratio (LWR) possibly indicates that the
source-sink system of rice was influenced by
Xco infection. Total chlorophyll and
chlorophyll b contents were considerably
reduced throughout the observation period as
a result of bacterial infection. The decrease,
however, in the level of chlorophyll a, starting
only from the third observation, indicates
that chlorophyll a was more sensitive to Xco
than chlorophyll b.

Detection of Papaya Ringspot Virus in
Papaya Seeds by ELISA. T. M. Espino, S. B.
Exconde, M. Maldo, & M. P. Bite. National
Institutes of Biotechnology and Applied
Microbiology (BIOTECH), UPLB.

Different parts of the papaya plant
including seeds were rapidly indexed against
Papaya ringspot virus (PRSV) by using the
diagnostic kit developed at BIOTECH.
Diagnosis involved the double antibody
sandwich ELISA wherein polyclonal and
monoclonal antibodies were used.

PRSV was detected in all the assayed
plant parts including the seeds obtained from
samples from Bulacan. PRSV was detected in
all the seed parts, particularly, in cotyledons.
Seed samples from Davao tested PRSV-

Pretreatment of PRSV-infected seeds
with Tween 80 and heat failed to eliminate

trunk and roots of papaya seedlings 2, 4, 6
and 8 weeks after planting. Highest
concentration of PRSV was found in the
roots. Transmission electron microscopic
examination of infected leaf dip preparations
showed that the morphology of the virus
particles was similar to those of the purified
PRSV particles.

Detection of PRSV with the use of the
diagnostic kit proved to be rapid and
sensitive. With the use of the kit, PRSV was
confirmed to be seed transmissible.

Frequency and Rates of Soil Drench
Application of Triadimenol to Control
Vascular Streak Dieback of Cacao. C. E.
Soria, J. O. Manalo, R. L. Prudente, & C. G.
Tabasa. Cocoa Investors, Inc., Davao del

Soil drench application of Triadimenol
at the rate of 2- liter solution per tree (1 ml
Triadimenol/liter of water) gave superior
curative and protective control against
vascular streak dieback of cacao caused by
Oncobasidium theombromae Talbot &
Keane. The fungicide was highly persistent
that it remained active for more than 90 days.
So far, this is the only systemic fungicide that
can stimulate vegetative and reproductive
recoveries of severely infected cacao trees
after a series of treatments every three

Cultural, Morphological, and Physiological
Characteristics of the Bacterium Causing
Leaf Blight of Anthurium (Anthurium
andreanum Lind). G. A. Tabo, & M. P.
Natural. UPLB.

Bacterial blight of anthurium was
observed in greenhouses in Los Banos,
Laguna. The disease, which was prevalent
during hot months, caused premature
yellowing of the leaves and consequent
defoliation of the affected plant.

The suspected causal bacterium was
isolated and evaluated for pathogenicity.
Results of cultural, morphological and
physiological tests showed that the bacterium
causing anthurium leaf blight was very similar
to Xanthomonas campestris pv. diffenbachiae

January- June 1990

Abstract of Paoers

Philippine Phytopathology Vol. 26

reported earlier as Xanthomonas

Pythium Rot of Papaya. L. B. Ros, G. G.
Divinagracia, L. D. Valencia, & P. R.
Magtibay. Institute of Plant Breeding (IPB),

Pythium sp. was readily isolated from
infested soil by using pieces of eggplant fruit
as bait. Affected plants showed rotting at the
base near the roots, and eventual yellowing
and consequent death of leaves. Morpholo-
gical studies showed that the fungus was P.
aphanidermatum (Edson) Fitz. It grew well
on potato dextrose agar and oatmeal agar.

Papaya seedlings of different ages were
inoculated with P. aphanidermatum. Older
seedlings proved to be more resistant.
Inoculations at 14 and 12 days after
emergence (DAE) resulted in disease
incidences of 93.71% and 7.82%, respectively,
indicating that older seedlings were more

Preliminary greenhouse screening of
103 papaya advanced lines and accessions
showed that three were resistant and five
were moderately resistant to the disease.

Stem Rot of Salago. T. O. Dizon, & T. T.
Reyes. IPB, UPLB

A hitherto unreported disease of salago
(Wikstroemia spp.) in the Philippines is

The disease characterized by wilting,
subsequent black discoloration of the
vascular tissues, and the development of
conspicuous blisters, which eventually
rupture exposing perithecia and conidia at
the advanced stage of infection, was observed
on entire affected branches and whole plant.

On the basis of morphology, the causal
fungus was identified as Diplodia sp.
Pathogenicity test involving mycelial
fragments of the identified isolate was
positive. Cultural characteristics of the fungus
were also studied.

Etiology of Ricebean Mosaic. F. L.
Mangaban, M. J. C. Malabanan and M. P.
Natural. IPB, UPLB.

A disease of ricebean characterized by
severe mosaic, vein-clearing and shoe-
stringing was observed to occur every season
in experimental plots.

The disease was readily transmitted by
mechanical inoculation (93%) and by aphids,
Aphis gossypii (90%) andA. craccivora (63%)
in a non-persistent manner. Inoculation using
crude infective sap resulted in chlorotic local
lesions in Chenopodium amaranticolor and
systemic mosaic in several leguminous plants.
The infected sap remained infective up to a
dilution of 10 at 50 C. It could be stored in
the refrigerator for 4 days without losing its
infectivity but was uninfective after storage at
room temperature for 2 days. In indirect
ELISA, the infected sap positively reacted
with the Peanut stripe virus and Blackeye
cowpea mosaic virus antisera but not with the
Peanut mosaic virus, Cowpea mosaic virus,
Tomato spotted wilt virus, Cowpea yellow
mosaic virus and Cowpea mottle virus

Infectiousness of Cercospora arachidicola
Hori and Phaeoisariopsis personata (Berk.
and Curt.) von Arx After Abscission of
Infected Leaves. R. A. Paningbatan and 0. S.
Opina. Visayas State College of Agriculture
(ViSCA), Baybay, Leyte and UPLB.

The effect of soil moisture on the
sporulation of Cercospora arachidicola Hori
and Phaeoisariopsis personata (Berk. &
Curt.) von Arx, respectively the causes of
early and late leafspots of peanut, on
abscised infected peanut leaflets was
evaluated. The viability of conidia on lesions
of air-dried leaves was determined at various
storage temperatures.

Both fungi on lesions of abscised
leaflets, which were either on the surface of
or buried 3-in deep in dry sandy loam soil,
remained infectious for 50 days with
decreasing sporulation capacity. In wet soil,
infectiousness was lost after 20 and 10 days
when leaflets were on the surface or buried,

Philippine Phytopathology

Vol. 26


At 0 C, conidia of both pathogens
remained viable for 10 weeks. Viability was
lost during the fifth and fourth weeks of
storage at 30 and 35 C, respectively. Conidia
of P. personata significantly survived longer
from 15 25 C than those of C. arachidicola.
This possibly explains for the apparent
predominance of late leafspot in previously
surveyed peanut fields all over the

Morphology of Sphaceloma Species Infecting
Fruit Crops. J. M. Dangan. National Crop
Protection Center (NCPC), UPLB.

Sphaceloma spp. cause warty
outgrowths or scabs on leaves, stems and
fruits, which, consequently, have a lower
market values.

This study was conducted to compare
and contrast the different Sphaceloma spp.
morphologically. The fungi were isolated on
glycerine agar by the poured plate technique.
Cultures of the isolated fungi grown on
potato dextrose agar at room temperature
were studied for colony and spore

Pathogenicity Test and Toxin Bioassay of the
Needle Blight Fungus Infecting Pinus
caribaea. R. S. Almonicar. Paper Industries
Corporation of the Philippines (PICOP),
Surigao del Sur.

Pathogenicity test and in vitro toxin
bioassay of the suspected causal organism of
needle blight of pines (Pinus caribaea) in
Bislig, Surigao del Sur were conducted.

Of the three test organisms used, only
the tentatively identified Pseudocercospora
sp. caused sooty blight in inoculated pines.
Sooty blight, a distinctive feature' of this
disease, developed 20-30 days after

In the laboratory, dipping pine needles
in toxin-containing culture broth resulted in
sooty spots and blight after 24 hr. Blight was
not observed in needles dipped in dextrose
broth only (control). Results indicated the

mvolvement or a toxm m mne disease

Occurrence and Distribution of Seedborne
Fungi of Rice in Certain Provinces of the
Philippines. J. K. Misra, E. B. Gergon, & T.
W. Mew. IRRI.

A total of 144 rice samples were
collected from different sites in Laguna,
Batangas, Cavite and in the Bicol region
during the dry and wet seasons of 1988-89
and analyzed for their fungal population
using the standard blotter method. The
analysis yielded 39 fungal forms belonging to
29 genera and infesting both apparently
healthy and discolored seeds. The percentage
of infestation by different forms ranged
differently at various locations. Among the
different locations, the common fungal forms
were evenly distributed except for Pyricularia
oryzae, Nakatac sigmoideum and Tilletia
barclayana during the dry season. During the
wet season, the distributions of Gerlachia
oryzae and Dreschlera oryzae were uneven. T.
barclayana was evenly distributed irrespective
of the season. Infestation of both apparently
healhty and discolored seeds was highest with
A. padwickii followed by Curvularia sp.

Effect of Storage on the Viability and Health
of Rice Germplasm. J. K. Misra, E. B.
Gergon, & T. W. Mew. IRRI.

A total of 50 samples of rice seeds were
collected from warehouses in Laguna from
December, 1987 to November, 1988. The
samples were studied for their fungal
contamination, moisture content,
germinability and production of abnormal
seedlings. The results indicated the influence
of storage period on seed viability. The
common abnormalities encountered in the
standard germination test were thick, thin,
short or long decayed roots or their absence,
and deformed or decayed coleoptiles or their

Diplocyclos palmatus L.: A New Weed Host
of Papaya Ringspot Virus. P. M. Magdalita,
R. G. Bayot, V. N. Villegas, & T. M. Espino.

PI I'pn Phg Vol60

The study was undertaken to identify
possible weed host(s) of Papaya ringspot
virus (PRSV) in the Philippines. Weeds
owing in papaya plantations with high
ncidence of papaya ringspot were observed
very closely for the presence of virus-like
symptoms. Weed species with such symptoms
were collected, their sap extracted separately
using mortar and pestle and inoculated
mechanically to healthy papaya seedlings.

Out of the twelve plant species tested,
only the sap of Diplocyclos palmatus was able
to induce on papaya seedlings symptoms
which were very similar to those of papaya
ringspot. D. palmatus, inoculated with crude
sap of PRSV-infected papaya leaves,
exhibited virus-like symptoms such as
mottling, crinkling, rolling and narrowing of
the leaves. Reciprocal inoculation of papaya
seedlings with crude sap of infected D.
palmatus also produced .typical symptoms of
papaya ringspot. This was further confirmed
by aphid transmission using Myzus persicae.
PRSV-like particles were observed by
electron microscopic examination of leaf dip
preparations of papaya inoculated with
infected D. palmatus sap. These tests prove
that D. palmatus is indeed a weed host of

Effect of Soil Moisture and Temperature on
the Incidence of Damping-off of Tobacco. P.
N. Dipon, & T. T. Reyes. University of
Eastern Philippines (UEP), Catarman,
Samar and UPLB.

Tobacco seedlings grown in soil
temperature tanks assembled in the
greenhouse were subjected to 35% and 55%
soil moisture and fluctuating daytime soil
temperature ranges of 26-28C, 29-34C, and
32-38C. Four soilborne pathogens associated
with damping-off of tobacco seedlings were
used in the study. Damping-off incidence at
different soil moisture levels and temperature
regimes, and the area under the disease
progress curve (AUDPC) were determined.

Incidence levels of damping-off were
significantly affected by the different
pathogens tested, soil temperature and
moisture, and the interaction of the three (P

Soil moisture of 55% and daytime soil
temperature of 29 34 C proved favorable for
disease development (AUDPC = 24 or 96%
infection). Damping-off was suppressed by
high soil moisture. On the other hand, soil
temperature of 32 38 C inhibited the
pathogens and seedling growth. The highest
incidence of damping- off at all moisture and
temperature regimes was due to Pythium
aphanidermatum. Soil moisture rather than
soil temperature was more limiting to
damping-off caused by Sclerotium rolfsii,
Rhizoctonia solani and Fusarium oxysporum
f. sp. nicotianae. Infection by these pathogens
were favored by low soil moisture of 35%
and soil temperature of 29 34 C (AUDPC
= 7.14 12.5 or 29% to 50% infection).

Alternate Hosts of Xanthomonas campestris
pv. dieffenbachiae (McCulloch and Pirone)
Dowson, the Causal Organism of Bacterial
Blight of Anthurium. M. J. G. Telebanco, &
M. P. Natural. UPLB.

Sixteen alternate hosts of Xanthomonas
campestris pv. dieffenbachiae, the cause of
bacterial blight of anthurium were identified.
The bacterium was able to infect Aglaonema
commutatum, A. marantifolium, Alocasia
thibautiana, Dieffenbachia amoena, D.
oerstedii, Philodendron (Emerald Queen),
Philodendron (Golden Erubrescens),
Philodendron x mandaianum, p. micana, P.
pittiere, P. panduriforme, P. squamiferum,
Syngonium erythrophyllum, S. podophyllum
and Schizocasia lauterbachiana. It failed to
infect P. selloum, P. wendlandii, Philodenron
(Majesty), Philodenderon (Variegated) and
Alocasia indica metallica.

The initial symptom in different hosts
was watersoaking of the infiltrated area 3-4
days after inoculation. The watersoaked
tissues later became yellow and eventually
turned into an irregular brown necrotic lesion
with a yellow chlorotic halo. As the disease
progressed, the lesion increased in size and
coalesced until the whole leaf turned brown
and dry.

Inoculation of reisolated X.. c. pv.
diffenbachiae heavily infected leaves, which
were prematurely abscissed from the stem,

Phllppirvo Phylopathology


confirmed that it was the causal bacterium, leaf area took place due to the absence c
Symptoms produced were similar with those secondary infection. The total leaf areas c
described for the first inoculation, resistant and moderately resistant varieties
were highly affected after 4 WAI.
Effect of Tungro Viruses on the
Development of Sheath Rot of Rice. M. A. Total leaf areas of infected rice varieties
Gill, & J. M. Bonman. IRRI. varied with the levels of nitrogen applied
Higher nitrogen levels neither brought about
Effects of rice tungro viruses on sheath further change in the total leaf area at th
rot (SR) of rice grown in the greenhouse later stage nor increase in the dry matter c
were studied. Three to four-week old plants BB-infected rice. The decrease in dry weigl
of cultivars IR36 and C039 were inoculated due to BB at the recommended nitrogen
with the viruses using the mylar cage method. level (100 kg N/ha) was not significantly
Virus-infected and healthy plants were different from those observed at othe
identified using a serological test. At early nitrogen levels. The considerable reduction i
booting, half of the plants were inoculated dry weight at low and high nitrogen level
with the SR pathogen, Sacrocladium oryzae, might be due to lack of source an
while the other half were uninoculated competition of sinks, and to maintenance c
checks. The incidence of SR and seed leaf area, respectively.
discoloration in all virus-infected plants was
noted. Highest SR incidence was observed in Nitrogen levels, disease severity an
RTBV- and RTBV + RTSV-infected plants crop growth parameters were correlate
of both cultivars. SR severity and lesion highly with reduction in leaf areas of varieties
length were greater in RTBV- and RTBV + inoculated at maximum-tillering stage. Lesio
RTSV- infected C039 plants and RTBV- lengths and diseased areas of susceptible an
infected IR36 plants. moderately resistant varieties at the early an
late stages of BB, respectively, significant]
Inoculation of both cultivars with the varied with nitrogen levels. Dry weights an
viruses did not significantly affect flag sheath percent filled grains of susceptible varieties
length. Reduction in panicle emergence and negatively correlated with disease
increase in percent partially emerged development. Healthy susceptible varietic
panicles resulted from S. oryzae-inoculated had more filled grains and higher 1,000-grai
C039 plants previously infected with the virus weights when grown at higher nitrogen level
except those infected with RTBV + RTSV. Such effects were not observed with infected
We conclude that RTBV altered the susceptible varieties.
physiology of rice making it more susceptible
to SR. The combined effects of RTBV and Survey of Nematodes Associated wit
S.oryzae on all parameters measured were Selected Vegetables Grown in Region XI. N
greater than the additive effects of the two N. Infante, & F. B. Castro. Regional Cro
pathogens when applied singly, thus, Protection Center, Department 4
idicating synergism. Agriculture, Davao City.

Effects of Bacterial Blight on the Growth of A survey of vegetable-growing areas ft
Four IR Varieties at Different Nitrogen plant parasitic nematodes was conducted i
Levels. K. S. Jin, & T. W. Mew. IRRI. two cities and nineteen municipalities i
Region XI and involved 107 farm(
The effects of bacterial blight (BB) on cooperators.
the biomass and leaf area of rice grown at
different nitrogen levels in the greenhouse Vegetables sampled included eggplant
during the dry season of 1989-1990 were tomato, cabbage, ampalaya, stringbeans an
studied. Reduction in the leaf area of the other legumes, onion and pepper. Nematod(
susceptible variety (IR56) was observed 4 identified to be associated with. the sample
week after inoculation (WAI) after which no were Helicotylenchus sp., Hoplolaimus sl
further considerable reduction in the total Pratylenchus sp., Rotylenchus s\

Abetraels Of PapoI

nnury aunu iw

Philippine Phytopatholony Vol.26

Tylenchorhynchus sp., Tylenchus sp. and
Meloidogyne sp.

Root-knot nematode (RKN) infestation
was observed to be moderately severe to
severe in areas traditionally or successively
grown to ampalaya as in San Isidro and Mati,
Davao Oriental. It was Only in Kalapagan,
Lupon, Davao Oriental where RKN was
positively associated with tomato and

RKN was also observed in Tagum and
Panabo, Davao del Norte, Koronadal and
General Santos City, South Cotabato. It was
in General Santos City that practically the
three sampling sites for ampalaya were found
to be positive for RKN.

The severity of RKN infestation in some
ampalaya and tomato sampling sites was such
that control measures would have to be
applied. The level of nematodes associated
with other vegetables, although not alarming,
had to be monitored nevertheless to avoid
high infestation levels.

Population Dynamics of Hirshmanniella
oryzae and Hirshmanniella mucronata on
Sesbania rostrata, Aeschynomene afraspera
and Rice cv. IR58. S. M. ESR. Hendro, J. C.
Prot and C. P. Madamba. UPLB and IRRI.

Experiments were conducted under
field and greenhouse conditions to estimate
the efficiency of S. rostrata, and A. afraspera
in controlling H. oryzae and H. mucronata.
Field experiments were conducted in two
irrigated rice fields naturally3infested with H.
oryzae (mean 595/dm of soil). A
greenhouse experiment was conducted in
pots with initial inocula of 0, 500, 5000, and
10000 nematodes/pot. Root and soil
nematode populations were estimated 0, 15,
30, 45, 60, 75, and 90 days after transplanting

In rice field plots, the root nematode
populations gradually increased until 45 DAT
during which a maximum was reached and
after which populations decreased until
harvest. Simultaneously, the number of
nematodes detected in the soil progressively
decreased until 45 DAT and then increased

again to reach population densities
approximately equal to the initial population

In S. rostrata and A. afraspera field plots,
the nematode root populations increased
progressively from transplanting to 60 DAT
during which the nematode soil population
decreased to less than 1/dm of soil.
Between 60 and 90 DAT, the nematode root
population decreased to less than 1/g of root,
whereas the nematode soil populations did
not i crease and remained at less than
1/dm of soil. Similar results were obtained
in the greenhouse experiment.

These results indicate that S. rostrata
and A. A. afraspera effectively controlled H.
oryzae and H. mucronata populations in field
and greenhouse conditions. Moreover, these
two legumes appear to act as trap plants for
the two Hirshmanniella spp.

Distribution of Hirschmanniella oryzae in the
Province of Laguna, Philippines. J. C. Prot.

A survey was conducted to estimate the
infestation level of H. oryzae and its
distribution pattern in Laguna. Soil and root
samples were collected from 84 fields (10
samples per field) at different rice growth
stages (i. e., 17 at maximum tillering, 18 at
flowering, and 49 at maturity).

Only 19 samples out of the 840 collected
did not contain detectable levels of H. oryzae
in the soil and the roots. The ayrage number
of nematodes detected per dm of soil and g
of roots were 516 (range, 0-19075) and 30
(range, 0-927), respectively. Population
densities of more than 200 nematodes per
dm of soil or 20 per g of roots were detected
in 539 samples. The average number of
nematodes detected per dm of soil at
maturity (764) was significantly higher than
at maximum tillering (154) and flowering
(181). The average number of nematodes
detected per g of roots at maximum tillering
(64), flowering (34) and maturity (18) were
significantly different from each other.

After chi-square goodness-of-fit tests,
none of the population distributions differed

Philippine Phvtopatholoav

Vol. 26

Ah~raa4. sf( Dana,.

ive binomial Sixty day after applic

variance of the population and M = mean of
he population). All the distributions can be
formalized by using the transformation: Y =
Ce(c = l-b/2) except for observations on
roots taken at maturity.

These results indicate that H. oryzae was
ubiquitous with high population densities in
irrigated rice fields i Laguna. Nematode
populations in surveyed areas followed a
negative binomial distribution. To compare
population densities of H. oryzae present in
different fields, the densities must be
estimated at the same stage of the rice crop.

Epidemiology and Control of Rubber Black
Stripe Caused by Phytophthora palmivora
Butler. J. P. Pedrosa and A. D. Raymundo.
Western Mindanao State University
(WMSU), Zamboanga City, and UPLB.

This study was conducted at ten rubber
plantations in Mindanao (Basilan,
Zamboanga del Sur, North Cotabato and
Davao del Sur) to assess the incidence,
severity, development and control of rubber
black stripe.

Black stripe was observed in all
plantations. Highest incidence of the disease
was recorded at University of Southern
Mindanao (USM) and Zamboanga Rubber
Corporation (100%) and lowest at Menzi
Agricultural Corporation (48.8%).

Disease severity varied among
plantations. Severity was lowest at Menzi
(16.0%) followed by Carbonnel (22.0%),
UPLG (24.6%), Firestone (25.8%), USM
27.2%), Glorianne (31.6%); Sandique
53.5%), Martinez (5.2%), Gallardo Farm
(62.7%) and Zamboanga Rubber
Corporation (90.9%) which had the highest.
Severity of black stripe increased with time.

Rate of infection from June to
September was slow. Black stripe was
significantly controlled with metalaxyl (7
sp/20 liters), caftafol (16 tbsp/liters) and
oxadixyl + mancozeb (15 tbsp/21 liters).

uu Lq.1UL~u aLJu.LaLUi J13 I.uuL Lu LMJ'a

Assessment of Yield Losses in Corn Due to
Virus. S. C. Dalmacio and G. P. Lozano.
Pioneer Overseas Corporation, Cabuyao,

A study was conducted to assess the
impact of virus infection on the yield of corn.

Assessed were corn hybrids which were
stunted and showing symptoms similar to
hose of maize stripe virus infection, and
nbreds showing symptoms characterized by
nosaic, mottle, stripe, and rosette.

In hybrids, reduction in cob weight
ranged from 2.92 to 100%, with an average of
57.15%. Reductions in inbreds were 70.12%
for those showing mosaic type of symptom,
)1.45% for mottle, 100% for rosette and
100% for stripe types of symptom. In general
inbreds with tropical background were more
tolerant than those with temperate

Quantitative Yield Loss Assessment in Rice
Due to Scald and Blast. S. B. Calvero, Jr., F.
L. Nuque and P. S. Teng. IRRI.

Literatures on yield losses of rice due to
leaf scald and blast are few. This study was
undertaken to assess quantitatively the
relationship of severity and, in the case of
blast, index to losses.

During the 1987 wet season, the severity
of leaf scald at IRRI rated 0 to 7 which
positively correlated with losses in yield and
yield components. Grain weight (yield) loss
ranged from 0 to 81.3 %. Similar trends were
observed for blast during the wet and dry
seasons in 1988 and 1989, respectively. Levels
of disease incidence, panicle blast severity
and disease index gave significant positive
correlation with losses in yield and its
Onuantitative assessments of the

HIIYII-VY I~I~~V ratrrm LM Do rer


i rnisi~pp.. mu r-lytopathoau luo.-.y

lumbers of filled grains and panicle with
disease parameters were done by generating
)redictive equations using stepwise multiple
egressionn analyses.

Epidemiological Basis of Resistance to
Rhizoctonia solani Kuhn in Sorghum. C. B.
Pascual and A. D. Raymundo. IPB, UPLB.

Rhizoctonia sheath blight development
n the susceptible cultivar, UPL Sg-5, and the
resistant accessions, CS-621 and CS-622, was

Disease level on the final observation
late, 49 days after initial symptom
appearance, was higher on UPL Sg-5 than on
CS-621 which had infection rates of 0.052 and
).031/unit/day, respectively. Relative to UPL
Sg-5, resistant accession reduced the rate of
disease development by 40.3 %.

Lesion size on Cs-621 and CS-622 was
significantly smaller than on UPL Sg-5. The
number of sclerotial bodies produced per
plant was significantly different among the
three host genotypes. CS-621 had the least
while UPL Sg-5 produced the most sclerotia.
Since sclerotial bodies serve as inocula,
previous planting of a susceptible cultivar
may contribute to higher incidence of
Rhizoctonia sheath blight in the next
cropping season.

Conjugal Transfer of a Broad Host-Range
Cosmid in Korean Isolates of Xanthomonas
campestris pv. oryzae. E. Y. Ardales, S. H.
Choi, J. E. Leach, H. Leung, T. W. Mew and
E. J. Lee. IRRI, Research and Development
Authority (RDA) and Kansas State
University (KSU).

A prerequisite to the genetic analysis of
virulence/virulence in Xanthomonas campes-
tris pv. oryzae (Xco) is the development of
gene transfer systems by which
extrachromosomal DNA could be introduced
into this pathogen. In bacteria, conjugation is
the principal means of gene transfer.

Fifty-three Czapek-Dox adapted Korean
Xco isolates were tested for the ability to
accept by conjugation the broad host-range
encm;il n.n APR whirh mnnfe.r tptracvcline

resistance. Two conjugation techniques were
tried --- liquid triparental mating and plate
mating. All the isolates tested produced
tetracycline resistant transconjugants on
Czapek-Dox plus tetracycline (CzT) plates.
Liquid-mating proved to be a better
technique than plate mating since this
technique required less time for the
formation of transconjugants. Mating
frequencies of six isolates ranged from 7.36 x
10- to 2.26 x 10" as compared with 3.15 x
10- for 86 CzAvi, the best mater among the
Philippine Xco isolates. In contrast to Xco
isolates from the Philippines, adaptation to
Czapek-Dox agar did not seem to be a
requirement for conjugation in Korean Xco
isolates. Six non-adapted isolates also
produced transconjugants on CzT plates.

Transposon Trapping in Xanthomonas
campestris pv. oryzae. M. R. Baraoidan, R.
Nelson, H. Leung and T. W. Mew. IRRI and
Washington State University (WSU).

Transposons are mobile genetic ele-
ments that can move within or between
chromosomes. The genetic role of these
elements is yet to be understood but they
have been detected genetically through the
phenotypic changes they cause when they
insert into certain genes.

Several transposons were isolated from
Xanthomonas campestris pv. oryzae (Xco)
through the use of trapping vectors. The
vectors allowed trapping of transposons
based on the insertional inactivation of a
conditionally lethal bacterial conjugation.
Trapped transposons in bacterial cells were
indicated by growth of colonies on medium
containing 5% sucrose and tetracycline; the
presence of a transposon was confirmed by
examining the plasmid DNA. Only one type
of transposon was trapped from some
isolates of Races 2 and 3 while several types
were trapped from a single isolate belonging
to Race 2. These transposons are now being
used as probes to analyze the population
structure of Xco.

Analysis of Introgression of Allen Resistance
Genes in Oryza sativa x 0. minute Progenies
Using DNA Probes. N. P. Oliva, R. Nelson,


Disease resistance has been transferred
from Oryza minute to rice by wide
hybridization. DNA probes are being used to
characterize the alien genetic material that
confers resistance. Three repetitive DNA
sequences (pA5-36, pB10, pOM4) that are
specific to wild rice (0. minute) have been
isolated. These repetitive DNA sequences
could be used as probes for analyses of alien
DNA introgression in progenies from an O.
sativa x 0. minute cross. Backcross, [55-1
(2n=35) was shown to be BC3 plants that
were derived from 55-1 (BC2) and have extra
chromosome(s) from 0. minuta (2n=25) to
2n=29). They were positive in Southern blot
analysis using pOM4 as probe while most
plants with only 24 chromosomes showed no
signal. These observations indicate that this
repetitive DNA sequence (pOM4) may be
pericentromeric and may not be useful for
studying introgression. Disease resistance has
been transferred from the wild species to two
BC2 plants with 24 chromosomes. These
plants, 75-1 (blast resistant) and 78-1
(bacterial blight resistant), are being
analyzed with the repetitive probes. In
addition, a similar DNA analyses of 0. sativa
x 0. minute progenies using single copy
mapped DNA markers is being undertaken
using restriction fragment length
polymorphism (RFLP) analysis.

Agronomic Value of Partial Resistance to
Blast B. A. Estrada, J. M. Bandong, T. W.
Mew, J. M. Bonman, C. K. Lim and E. J.
Lee. IRRI and RDA, Korea.

Experiments were conducted from 1987
to 1989 in the Philippines and Korea to
evaluate the effectiveness of locally adapted
partially resistant (PR) cultivars in managing
rice blast and reducing yield losses. For
Philippine trials, cultivars IR36 (PR to leal
and neck blast), IR66 (susceptible to leal
blast but PR to neck blast) and IR5C
(susceptible to both leaf and neck blast) were
used. PR japonica cultivars Seomjin and
Bonggwang and susceptible varieties
Chucheong and Daechang were selected foi
Korean trials. Yield loss and neck blast
incidence were positively correlated in 6 trial

negligible yield losses were recorded for PR
cultiars IR36 and Scomjin in the Philippines
and Korea, respectively. Similarly, Philippine
variety IR66 exhibited low neck blast
incidence and low yield losses. PR varieties
Bonggwang showed intermediate neck blast
incidence (16.2%) and yield loss (31.2%) in
Korea. Maximum yield losses of susceptible
checks were 20.9% for IR50 and 50.2% for

For less conducive environment like the
Philippines, partial resistance alone can be
used to manage rice blast. Under highly
conducive conditions like those of Korea,
cultivars with high levels of partial resistance
alone will be effective in managing the
disease. However, additional control tactics
will be needed for cultivars with lower levels
of resistance.

Quantitative Resistance of F, Generation of
Corn Hybrids to Philippine Downy Mildew.
A. D. Raymundo and A. T. Aquino. IPB,

Most commercial corn hybrids seeds are
treated with the fungicide metalaxyl for
protection against Peronosclerospora
philippinensis (Weston) Shaw which causes
Philippine corn downy mildew. In many corn
growing areas, F generations of these
hybrids are planted without metalaxyl
treatment. This increases the chances of an
epidemic since many parental lines are
derived from susceptible foreign sources.

F2 generations of hybrids, entered in
the National Cooperative Testing Program
implemented by the College of Agriculture,
UPLB, were assessed for severity of infection
using the spreader technique which involved
the inoculation of seedlings in infector rows
around the experimental plot prior to the
planting of F2 seeds.

Results showed that the F, generation
of most hybrids were suscepTible. Some
hybrids appeared to possess resistance to P.



Screening of Peanut Lines and Accessions
for Low Seed Transmissibility of Peanut
Stripe Virus (PSTV). M. J. C. Malabanan
and M. P. Natural. IPB, UPLB.

Seed transmissibility of peanut stripe
virus (PSTV) in different peanut
lines/cultivars was evaluated using the direct
antigen coating-enzyme-linked immunosor-
bent assay (DAC-ELISA). Of the 101 entries
screened, 27 entries- did not demonstrate
transmissibility of the virus by seed. Highest
transmission was exhibited by
lines/accessions Pn 11, Pn 82-68-94,
Lampang and Pn 48-90 with 12.2, 11.0, 11.0
and 10.0% transmissibility, respectively.

Differentiation of Thirty-Three Isolates of
the Rice Sheath Blight Pathogen
(Rhizoctonia solani Kuhn) Based on Hyphal
Anastomosis and Cultural Characteristics.
H. Than and T. W. Mew. IRRI.

Isolates of Rhizoctonia solani Kuhn (Rs)
prevalent in rice fields were differentiated
into anastomosis groups based on hyphal
anastomosis on glass slides coated with 1.5 %
water agar and types of fusion on potato
dextrose agar.

Various combinations of Rs isolates
exhibited perfect fusion which was indicative
of vegetative compatibility. Imperfect fusion,
evidenced by clear zone formation between
tested colonies, was demonstrated by many
other different combinations of Rs isolates,
thus, indicating vegetative incompatibility.
These results indicate variations among Rs
isolates, grouping of Rs isolates into more
than one anastomosis group and the
existence of similar isolates at different
places. Furthermore, examination of types of
colony fusions on PDA proved to be an
efficient method for grouping a large number
of Rs isolates into anastomosis groups in a
short period of time.

Cluster analysis of the Rs isolates by
using the UPGMA was carried out based on
65 attributes like hyphal growth, number of
sclerotia formed, size of sclerotia,
pigmentation, and formation of aerial
mycelia and pseudosclerotia on a variety of

formed of which Clus 2, comprised of 36% of
the evaluated isolates, was the largest.

These results indicate that the highly
variable Rs isolates could be grouped based
on cultural characteristics.

Pathogenic Variability of Erwinia
chrysanthemi Isolates from Corn in
Mindanao. B. T. Dionio and A. D.
Raymundo. University of Southern
Mindanao (USM), Kabacan, North
Cotabato and UPLB.

Fourteen isolates of Erwinia
chrysanthemi, causing bacterial stalk rot of
corn, were collected from various localities in
Central and Southern Mindanao. Variability
in terms of percent infection and percent
toppling of Pioneer 3208 hybrid was
observed. Incidence (70.9%) and toppling
(42.0%) were highest with isolate D1. The
onset of infection appeared to be a key
parameter. For instance, with isolates D1 and
E2 infection started 4 and 6 days after
inoculation, respectively. With the many
other isolates, however, infection was
observed only 40 days after inoculation. A
number of isolates did not cause toppling of

Disease Reactions of Eleven Sorghum
Selections at USMARC-USM, Kabacan,
Cotabato. N. G. Tangonan, F. R. Alejandro,
W. B. Malacad, P. R. Miral and W. B.
Escalante. University of Southern Mindanao
Agricultural Research Center (USMARC),
Kabacan, North Cotabato.

This study aimed to identify high
yielding sorghum cultivars with broad
spectrum resistance to pests and diseases and
which would later be recommended to the
Philippine Seed Board for evaluation and
eventual release as varieties.

Results showed that all 11 entries when
'compared to UPLSg5, the local check which
was rated moderately susceptible, were found
resistant to prevailing common diseases
attacking sorghum at USMARC-USM such
-- *-- -- -- ~--t-i--<--. --

Vpr ,, ., _Vle, _,v"v M


LU.Lt MLaIluMu 1mauu% auM UFVi VU Uy I.UL
International Crops Research Institute for
the Semi-Arid Tropics (ICRISAT) where 1
= no symptom and 5 = more than 40% of
the leaf area infected. Other diseases noted
were target leaf spot, gray leaf spot, bacterial
stalk rot, and head molds; however, these
were regarded of minor importance.

Of the 11 cultivars, USMARC 212
obtained the highest grain yield of 6 tons/ha
followed by USMARC 208, USMARC 214
and USMARC 216 with yields of 5.7, 5.6, and
5.5 tons/ha, respectively. Plant height ranged
from 182.13 to 260.58 cm, days to 60%
flowering, 59 to 67, and head length, 26 to 30

Promising Corn Germplasm Resistant to
Downy Mildew. N. G. Tangonan. E. R.
Bautista, F. R. Alejandro and J. A.
Arguelles. USMARC.

A total of 2,673 corn germplasm which
consisted of 1,218 intermediate white flint,
1,121 early white flint, 320 tropical late yellow
coming from CIMMYT (Centro
International de Majoramiento de Maize y
Trigo) and 14 IPB (Institute of Plant
Breeding, UPLB) lines were screened at the
University of Southern Mindanao
Agricultural Research Center (USMARC)
for reaction to downy mildew caused by
Peronosclerospora philippinensis. Using the
rating scale suggested as standard for
Philippine downy mildew during the National
Symposium Workshop on Evaluation of Host
Resistance to Pathogens and Insect Pests in
Corn and Sorghum held at USMARC-USM
from July 20-21, 1989, 54.51% were found
resistant, 26.60%, intermediate, and 18.98%,

This study is part of a project that aims
to develop open-pollinated corn varieties
resistant to downy mildew infection.

Screening of Rice Varieties for Tolerance to
Rice-Tungro Associated Viruses in Rice
Varieties by Severity Index Scoring and
Serology. R. C. Cabunagan, R. D. Daquloag,
Z. M. Flores and H. Koganezawa. IRRI.

A"a, Lw o JUI LU IulLILIL Ju i FvOuau4IL
varieties for resistance or tolerance to
infection by rice tungro-associated viruses
(RTV) was used on 15 selected varieties
which were indexed by serology for infection.
Each variety, which was replicated in 3 pots,
was planted at 20 seeds per pot. Ten days
after planting, a pot of each of the 15
varieties was inoculated using 10 viruliferous
green leafhoppers/seedling for 3 hr in a cage.
Seedlings were individually scored using the
new scoring method 4 wk after inoculation.
Leaf samples were collected from each
seedling and indexed in the laboratory for the
presence of RTV using ELISA.

Reactions were classified as follows:
severity index score 1-3 = resistant, 4-6 =
intermediate, and 7-9 = susceptible.
Varieties Utri Rajapan (Acc. No. 16684),
ARC 11554, Pankhari .203, Balimau Putih,
Utri Merah (Acc. No. 16680)' and
Tilockkacharai were resistant. Less than 10
% infection was recorded only for ARC
11554 and Utri Merah evaluated by ELISA.
Varieties Utri Rajapan, Pankhari 203,
"n-"- -- T--.*I -_ 1 ni_ ii __


rurusrw vl r~plr


62 Philippine Phytopathology Vol.26

temperatures, and by using different Dosages and Methods of Application. I. C.
inoculum levels. Tandingan and A. E. Ampo. USM.

Four reaction types were observed in Seven-year old cacao trees infected with
incompatible line-race combinations when vascular streak dieback (VSD) were assessed
inoculated at the flag leaf stage, 85 days after using an arbitrary scale of 0 4. The effects
sowing (DAS). Typical yellow lesions were of the rates of triadimenol (Bayfidan EC .25
observed in combinations using lines with a. i. at 5, 10 and 15 ml/15 liters of water as
Xa-4 and Xa-5 while limited brown lesions mainplots) and methods of application (i. e.,
resulted in lines with Xa-3. Lines with Xa-7 soil drench and foliar spray as subplots) were
were either asymptomatic or had restricted observed for a ten-month duration and
light yellow lesions. Lines with X-10 did not analyzed in a split-plot design.
show any symptoms. Some incompatible
combinations gave rise to different reaction There were no significant differences in
types on different flag leaves of the same VSD severity after six monthly applications
plant. In addition to typical yellow lesions, of triadimenol using the two methods and
asymptomatic lesions, which were similar to three dosages. Hence, dosages were
those of distilled-water inoculated leaves, increased to 10, 15 and 30 ml/15 liters of
were found in lines with Xa-5. The line with water. After. four monthly applications,
Xa-3 inoculated with race 4 developed brown infection was significantly reduced among
and typical yellow lesions, triadimenol-treated trees. Trees drenched
with 20 ml triadimenol/15 liters of water
Reaction to infection varied with plant were the least infected.- Results suggest that
age. As a result of adult plant resistance, the use of fungicide at recommended dosage
elongated yellow lesions were observed in the may not be effective at higher disease
line with Xa-3 inoculated 35 DAS. Similar pressure especially when infection reaches
symptoms were observed in the line with Xa- most of the secondary branches.
4. Asymptomatic lesions were not observed
in the line with Xa-5 until later stages. Lines Efficacy of Fungicides Against Black Stripe
with Xa-7 developed yellow lesions which did of Rubber. T. B. Bayaron and T.S. Rivera.
not appear at later stages. A combination USMARC.
consistently resulted in two reaction types
when inoculation was independently carried Various rates and frequencies of
out at 65 and 85 DAS. applications of Maneb and Sandofan, which
were previously found effective against black
In inoculum density and temperature stripe of rubber caused by Phytophthora
studies, no symptom was evident when an palmivora Butl., were evaluated further.
inoculum density of 10' cfu was used.
Increasing the inoculum density from 10 to Tapping of rubber trees was suspended
10 cfu resulted in increased lesion size and during the entire experiment. The design
shorter latent period. Generally, no changes used was split-split-plot.
in reaction types were observed but a few
line-race combinations did not show Rubber trees with a severity rating of
symptoms at all. No change in reaction types 4.0 were used as experimental trees. These,
was observed at different temperature levels trees had brown to black lesions just above
(i. e., 20/17, 29/21 and 35/27 C day/night the tapping panel.
temperatures). Higher temperature resulted
in shorter latent period and increased lesion The fungicides were brushed on the
size. surface of tapping panels. The rates tested
were the recommended rates (RR), RR + 10
Development of Integrated Disease % of RR and RR 10 % of RR. Frequencies
Management Against Vascular Streak of application were once, twice and four
Dieback of Cacao. I. Chemical Control of times a month. Fourteen days after the last
VSD Using Triadimenol at Different

January June 1990 Abstracts of Papers 63

fungicide application, efficacy of the Pratylenchus zeae on rice cv. UPL Ri-5 and
fungicides was evaluated, its effect on yield.

Applications of Maneb and Sandofan In the greenhouse experiment, 10 day-
were significantly effective in controlling the old seedlings were inoculated with 0, 250,
disease. Trees treated with Maneb had fewer 500, 1,000, 2,500 and 5,000 nematodes
lesions and a lower severity rating of 1.31 .Nematodes were applied as single or ten-
compared to Sandofan-treated ones with a inocula at 3-day intervals. Significant
severity rating of 2.03. reduction in yield by at least 69 %, number of
panicles by at least 54 %, weight of filled
Unlike application rates, different grains per panicle, panicle length and plant
frequencies of application resulted in height were observed at all inoculum levels.
significantly different disease severities.
Fungicide application at the frequency of 4 The effects of corn, cowpea, mungbean
times a month at a 5-day interval significantly and rice on the population density of P. zeae
decreased disease severity to 0.92. Twice and were studied in a naturally infested field.
once a month applications resulted in disease Yields of rice grown after two cultivations of
severity ratings of 1.01 and 1.49, respectively, these crops were measured.

Development of Integrated Disease Nematode population density was
Management Against Vascular Streak significantly high (>4,000/dm3 of soil) after
Dieback of Cacao. II. Cultural Control of two cultivations of cereal grops but was
VSD Using Different Pruning Frequencies. I. drastically reduced (<30/dm" of soil) after
C. Tandingan and A. E. Ampo. USM. two cultivations of leguminous crops. Yield of
rice grown after two cultivations of each crop
VSD-infected, seven-year old SCA correlated negatively with the nematode
cacao plants were surveyed and assessed for population density estimated at the end of
severity. Effects of different pruning the preceding cutlivation. Thus, legume-rice
frequencies such as every 2, 3, and 4 wk and rotation resulted in higher rice yield than
the no pruning control were analyzed in cereal-rice rotations. Specifically, the rice-
randomized complete block design. rice rotation resulted in rice yield 37 % lower
than that resulting from the cowpea-rice
Four months after initial pruning, the rotation.
level of VSD was significantly reduced in
three clones, SCA 6, SCA 12, and SCA 49. These results indicate that P. zeae is a
Pruning at an interval of 2, 3.and 4 wk had potentially important pathogen of upland rice
similar effects in reducing the disease level, and can be controlled by rotating rice with
Furthermore, pruning once a month had legumes such as cowpea and mungbean.
eradicated the disease from sample trees.
This practice was effective due to the Suppression of Clubroot of Cabbage by Soil
relatively lower level of disease, i. e., Solarization. S. P. Milagrosa and G. W.
pathogen was restricted mostly to the tertiary Riethmacher. Benguet State University
branches. Moreover, pruning was done (BSU), La Trinidad, Benguet.
before the rainy season which -was the
favorable period for the disease. Increase in soil temperature as a result
of covering the soil with transparent plastic
Pratylenchus zeae on Upland Rice and Its mulches was associated with reduced
Control by Crop Rotation. D. M. Matias, J. clubroot incidence on cabbage grown in three
C. Prot and T. Aung. IRRI and ARD- locations.
Gyogon, Rangoon, Burma.
Solarized plots had significantly higher
Greenhouse and field experiments were cabbage head weight compared to that of
conducted to evaluate the pathogenicity of untreated plots. The highest mean weight was
obtained from the lime-solarization

64 Philippine Phytopathology Vol. 26

treatment followed by those obtained from amounts of rice bran as bulking agent were
treatments with solarization. Lime treatment amended with spores of Trichoderma. The
alone also reduced clubroot infection and amended mixtures were dripped into a
was just as effective as solarization treatment solution of CaCl2 for pellet formation. Spore
alone, viability was determined prior to, 24 hr after
and at a monthly interval after pellet
The mean number of heads formed in formation.
untreated plots was significantly fewer than in
lime-solarization, and water-lime-solarization A set of pellets was air dried and stored
treated plots. The solarization-lime-water at 28 C while another set was stored
treatment not only resulted in more but also immediately at 10 C. Spores in pellets stored
heavier harvested heads indicating that this at 10 C were still viable after 1 year and 5
combination effectively reduced clubroot months with viability declining with time. Air
infection. dried pellets had viable spores up to only 8
months after which very few colonies were
Mechanical, Biological and Chemical noted in some isolates.
Control of Banded Leaf and Sheath Blight of
Maize Caused by Rhizoctonia solani. S. C. Pellets in sterilized soil produced 88 -
Dalmacio, G. P. Lozano, R. S. de la Pena and 97% more colony forming units (cfu)/g of
B. L. Candole. Pioneer Overseas soil than in unsterilized soil. One-week old
Corporation, Cabuyao, Laguna and IRRI. pellets produced 41 60% more cfu/g of soil
particularly during the second month
A study on the mechanical control, and compared to 4-week old pellets which, during
simultaneous experiments on the biological the first month, produced more cfu/g of soil
and chemical control of banded leaf and which gradually decreased thereafter.
sheath blight of corn caused by Rhizoctonia
solani were conducted. Fresh 1-week old pellets yielded more
colony forming units compared to dried
Removal of infected corn leaves proved pellets of the same age. The opposite was
to be effective in controlling the upward noted with 4-week old pellets.
spread of lesions.Of the five tested
fungicides, namely, Validamycin, Tilt, No significant difference in efficacy was
Rizolex, Rovral and Benlate, Validamycin observed among the different amounts of
was the most effective in reducing lesion bulking agent used. This method of
spread. encapsulating Trichoderma for enhanced
survival and proliferation in the soil proved to
The efficacy of four biocon agents, viz., be promising.
IRRI Bacterial Isolate 33, IRRI Bacterial
Isolate 784, Trichoderma aureoviride and T. In Vitro Antagonism of Sclerotium rolfsii by
harzianum, in controlling maize blight were Trichoderma Isolates and Effects of Selected
compared with that of Validamycin. Pesticides on the Organisms. Fernandez and
Validamycin still gave the best control R. M. Gapasin. ViSCA.
followed by T. harzianum.
Under laboratory conditions, all
Studies on the Survival and Proliferation in Trichoderma isolates tested, except T.
Rice Soil of Trichoderma Isolates harzianum IRRI isolate, were found effective
Encapsulated in Alginate Pellets. I. R. S. as biocontrol agents based on their ability to
Soriano and T. W. Mew. IRRI. suppress the growth of S. rolfsii and colonize
the area where the latter had established. All
The biological characteristics and resulting sclerotia were infected with the
efficacy as a delivery formulation of antagonists and failed to germinate when
Trichoderma isolates encapsulated in alginate seeded on potato dextrose agar (PDA). The
pellets were evaluated. Suspensions isolates of T. harzianum, the Samar and
containing 1 % sodium alginate and varied Leyte isolates of T. aureoviride and those of

ne 1990 Abstracts of Papers

with the latter as manifesto
ation of inhibition zone. i
SCA did not inhibit the growth
Colonized the latter by direct]
otial bodies.

valuation indicated that variot
affected the growth an
' T. aureoviride and S. rolfsi
entration negatively correlate
growth and sporulatiol
iradan 3G, a nematicidi
sporulation of T. aureoviria

of the tested leaf extracts
capulco, kamote, tanglad
ulasiman and saluyot.

inst Pathogens of
Pcn and V. R.

of leaves of kutsai, ati
ndakaki, uray, kamantigui
ulco. papaya, among mari;
oteng baging (green), tanglac

, laguna, lantana ana luya were tested
t Helminthosporium oryzae, H. maydis,
ghicola, Curvularia oryzae, C. lunata
usarium moniliforme, and compared
)elsene Mx, a commercial fungicide.
extracts were mixed with potato
se agar on which the test fungus was
SFungal colony growth was measured
,4 and 7 days of incubation.

tracts of leaves of kamias. kutsai,
tigue, camote, ampalaya, okra,
nan, saluyot, mayana, among maria,
, calamansi and sampalok inhibited
growth of C. lunata with kamias being
lost effective. Colony growth of C.
was inhibited by leaf extracts of
nan, sampalok, suwag kabayo,
taka, luya, kutsai and kamantigue.
ansi leaf extract was most effective
t colony growth of C. oryzae which was
strolled by extracts of uray, sambong,
e and ampalaya. Only the extract of
Ltigue was inhibitory to F. moniliforme
only those of calamansi and sailing
inhibited colony growth of H. maydis.

Phlipie.. . ..hloy ol2


Efficacy of Oxadixyl Against Phytophthora
infestans in White Potato. L. M. Villanueva.

Wet and dry season trials were
conducted at the Benguet State University
Experiment Station, La Trinidad, Benguet
from 1985-1986 to evaluate the efficacy of
Sandofan M8 (oxadixyl) in controlling potato
late blight and consequently assess its effects
on yield. Seven fungicide treatments were
used, viz,Sandofan at 1.5 kg/ha applied at a
7-day interval; Sandofan at 1.5 kg/ha, 10-day
interval; Sandofan at 2.0 kg/ha, 15-day
interval; Daconil 75WP (Chlorothalonil) at
4.0 kg/ha, 5-day interval; Dithane M-45
(Mancozeb) at 4 kg/ha, 5-day interval; and
Curzate M (Cymoxanil + Mancozeb) at 4
kg/ha, 5-day interval. Untreated plants
served as control. Granola, a susceptible
variety of potato, was used in randomly
distributed treatments in four replicates.

Results of the two trials showed that all
the Sandofan treatments were comparable in
efficacy to the standard fungicides used. A
substantial increase in yield was also noted in
all treated plants, and the untreated control
gave the lowest mean yield.

Screening Methods for Selection of
Antagonistic Bacteria for Biological Control
of Rice Diseases. A. M. Rosales and T. W.
Mew. IRRI.

A series of methods were used to test
bacterial strains from ricefields against
seedborne, foliar and sclerotia-forming
fungal pathogens of rice. Standard blotter
and seed germination techniques were used
for seedborne diseases. The seed germination
test was done by bacterizing seeds and
placing them in uncovered plastic dishes or
trays. In the blotter method, bacterized seeds
were arranged in plastic plates with
moistened filter paper and incubated at 28 C
with alternating cycles of 12 hr of light and
dark periods for 5 days. Using the blotter and
seed germination methods, bacteria from
paddy fields were classified into three groups:
those that promote seed germination and

enhance seedling vigor; those that have no
effect on seed germination; and those that
are deleterious to seed germination.

In selection of bacterial isolates against
sclerotia-forming pathogens such as R.
solani, detached leaf/sheath method and
seedling test was used. Detached
leaves/sheaths of susceptible variety sprayed
with bacterial suspension (10 cfu/ml) were
inoculated with sclerotia of R. solani.
Simultaneously, bacterized seeds were
planted in plastic containers with field soil
mixed with rice hull-rice grain inoculum of R.
solani. Results of these tests indicated that
most bacteria from ricefields suppressed
sheath blight development.

As part of the effort of IRRI to develop
strategies for rice blast management,
bacterial isolates were screened in the
laboratory by dual-culture method. One
hundred eighty-three isolates were inhibitory
to mycelial growth of P. oryzae. The diameter
of inhibition zone ranged from 10 to 50 mm.
These methods could be used for screening
antagonistic bacteria against three groups of
rice-fungal pathogens.

Variants of Rice Grassy Stunt Disease in the
Philippines. G. B. Jonson, H. Koganezawa,
T. W. Mew, N. B. Bajet and V. J. Calilung.

The range of symptoms of rice grassy
stunt (i. e., from very severe to very mild) and
the shift of TNI plant from being susceptible
to being considerably resistant to RGSV
prompted us to study the different variants of
the virus based on symptomatology,
transmission characteristics of Nilaparvata
lugens and host reaction.

Of the seven isolates collected from the
greenhouse and field, four distinct, stable
isolates designated as M3 (very mild), M9
(moderately mild), SC (moderately severeJ
and S2 (severe) were obtained through a
series of transfers using N. lugens.

Vol. 26

Philippine Phytopathology

Abat~nttn nf Pansy.

TNI seedlings artificially inoculated with
M3 had very mild symptoms and looked
almost similar to healthy plants. M2 induced
slight stunting, less profuse tillers with erect
growth habit, and narrow and slightly
yellowed leaves. SC induced profuse tillering
and spreading growth habit. Plants inoculated
with SC were slightly shorter than those
inoculated with S S2 induced severe
stunting, less pro use tillers, spreading
growth habit, and narrow and yellowed leaves
with rusty necrotic lesions. The effective
incubation periods of M, M2, SC, and S in
TNI plants were 26, 22, 14 and 11 days,
respectively. Percent active transmission
varied among isolates: 0 2.6 % for M-; 9.2 -
15.3 %, M2; 5.0 9.0 %, SC; and 1.7 -8.0 %,
S2. Effective incubation periods in the insect
vector were 11 and 9 days for M, and M,
respectively, and 7 days for both SC and S2.
All isolates were persistently transmitted by
N. lugens in a more or less intermittent
pattern with no transtadial blockade

Reactions of Oryza nivava and other O.
nivara derived varieties to the four RGSV
isolates indicated that these varieties were
resistant to both M3 and S, but susceptible
to M2 and intermediate to SC.

Effectiveness of Revised Alkaline
Phosphatase-Conjugated IgGs Raised to
Z. M. Flores, E. R. Tiongco, R. C.
Cabunagan and H. Koganezawa. IRRI.

The effectiveness of reused alkaline
phosphatase-conjugated IgGs was examined.
Conjugates of IgGs to rice tungro bacilliform
virus (RTBV), rice tungro spherical virus
(RTSV), rice grassy stunt virus (RGSV) and
rice ragged stunt virus (RRSV) diluted 500X
and 2000X in phosphate buffer saline -
Tween 20 (PBST) were used repeatedly in
the double antibody sandwich ELISA.
Extract dilutions of 20 and 40X (w/v) were
prepared from infected rice.

Results showed that no significant
difference in absorbance values was observed
using freshly prepared and reused conjugates.
Gradual decrease in absorbance values,
however, resulted from repeated conjugate

usage. The absorbance values obtained by
reusing RBTV and RGSV IgG conjugates
five times were significantly higher than those
of the healtly control. Conjugates of RRSV
and RTSV IgGs were effective up to fourth
and third reuse, respectively. Since enzymes
are expensive, reuse of conjugates at least
once translates into a savings of about 8 % of
the total cost.

A Clear-Contrast Staining Technique for
Ultrathin Rice Leaf Sections to Observe
Host-Parasite Interaction of the Rice Blast
Disease. M. A. Bernardo, R. Nelson and E.
Roumen. IRRI.

To gain better understanding of the
host-parasite interaction of rice blast,
ultrathin sections (15 um) of inoculated rice
leaves were studied. This technique permits a
detailed study of different host cell types (i.
e., bulliform, epidermal, parenchymal, and
vascular bundles) affected by the invasion of
the fungus. Penetration and colonization by
the blast fungus can be clearly observed since
the profile anatomy of the leaf is exposed.
However, with the Sass Safranin-Fast Green
procedure, the blast fungus cannot be easily
observed and distinguished from the host
cells because they do not stain differently. An
attempt was therefore, made to use the
optical brightener Uvitex (Ciba Geigy) to
stain the blast fungus. When sections stained
with Uvitex were observed by epifluorescence
microscopy, the blast fungus fluoresced green
and could be easily detected and
differentiated from the light yellow
parenchymal host cells. The details of the
compatible interaction exhibited by the rice
variety C039 P06-6 combination and the
incompatible interactions as shown by IR68 -
P06-6 and the wild rice species Oryza minute
- P06-6 combinations will be shown using the
previous and the new staining technique.

Occurrence and Localization of Rice Tungro
Bacilliform and Spherical Viruses in Host
Cells of Tungro Infected Rice. F. C. Sta.
Cruz, H. Koganezawa and H. Hibino. IRRI
and National Agriculture Research Center,

The occurrence and localization of
tungro bacilliform (RTBV) and spherical

--~~--~~--~~- Ah- traeft of Pe-- al


PhIlIppIne Phytopathology voi. Z~

(RTSV) viruses in host cells of tungro
spherical rice variety TNI was studied to
understand the cytological aspect of host-
virus interactions in tungro infected plants.
The particles of RTBV and RTSV were
found in phloem cells but neither in
mesophyll cells of tungro infected plants at
all stages of infection nor cells of healthy
plants. The cells containing virus particles
were mostly found at the outer margin of
phloem tissue. The virus particles were
mostly observed in the cytoplasm but no
particles were associated with the nucleus.
Single particles or aggregates of RTBV were
found scattered in the cytoplasm. RTSV
particles were scattered singly, embedded in
masses of filamentous or granular inclusions
in the cytoplasm, or found as crystalline
aggregates in the vacuole. Cells with RTSV
were mostly 'associated with vesicles
containing fibrils. RTBV and RTSV occurred
similarly in host cells of rice infected with
RTBV alone, RTSV alone or both RTBV
and RTSV. In plants infected with both
RTBV and RTSV, cells may contain RTSV
only, RTBV only or both RTBV and RTSV.
The inoculated plants showed negative
reaction to RTBV and RTSV by ELISA 3
days after inoculation (DAI) and no virus
particles were observed in sections of
inoculated plants. RTBV and RTSV were
observed in cells of infected plants which
reacted positively by ELISA. No significant
differences in the number of infected cells
was observed 7, 15, 30, 45, 60 and 75 DAI.
However, the number of virus particles per
cell was smaller 7 DAI than during the later
stages of infection. At 90 DAI, relatively
fewer cells contained the virus.

Potential Disease of Sesbania rostrata in the
Philippines. R. G. Bayot, E. T. Cadapan and
R. R. Renon. NCPC, UPLB.

A two-year survey (1987-1989) was
conducted to identify the potential diseases of
Sesbania rostrata under lowland and upland
conditions. Plants were monitored at
different stages of growth at the IRRI
experimental and IPB production farms.
Diseased specimens were collected,
examined microscopically and the pathogens
isolated using appropriate media.

The diseases found attacking S. rostrata
in the lowland were Rhizoctonia stem blight,
Cerospora leaf spot and mosaic. In the
upland, the most common diseases were
damping-off, root knot and mosaic. A very
low incidence of bacterial wilt, caused by
Pseudomonas solanaceamm, was also
observed in the upland. The Rhizoctonia sp.
that attacks S. rostrata also causes rice sheath
blight. The virus that causes mosaic
symptoms in S. rostrata produced the same
symptoms in soybean when inoculated
mechanically. The root-knot nematodes in S.
rostrata also attacked other crops such as
tomato, eggplant and okra. The bacterium
(P. solanacearum) isolated from S. rostrata
was found pathogenic to tomato. These
findings indicate that S. rostrata is susceptible
to certain plant diseases and can serve as
alternate host to plant pathogens attacking
some major crops in the Philippines.

Fruit Rot: A Phytophthora Disease of
Coconut. E. C. Concibido and R. G. Davide.
Philippine Coconut Authority (PCA), Davao
and UPLB.

This study aims to present information
about fruit rot of coconut for proper

The disease which was first reported in
Mindanao is known to occur in big coconut
plantations. The disease attacks MAWA
hybrids, yellow and orange dwarf cultivars of
coconut. It causes the premature falling of
unripe nuts. Initial study indicates that the
disease is unrelated to wet bud rot.
Phytophthora is constantly isolated from
infected samples.

Rapid Purification of Leaf Extracts for
Enhanced Detection of Coconut Cadang-
cadang Viroid. M. T. R. Ignacio and M. J. B.
Rodriguez. Philippine Coconut Authority
(PCA), Albay.

To enhance the detection of coconut
cadang-cadang viroid (CCCVd) in samples
electrophoresed using polyacrylamide
gels,extracts from diseased coconut. leaflets
were rapidly purified with MnCL1 which
---mna ;nA,rfr;.n hnt n6..-lt n.Ae. .that

Vol. A

Philippine Phytopatnology

Jaur ueiAbtat fPpr

extraction. Of the various MnCL
concentrations and reaction time
combinations tried, treatment of crude
nucleic acid extracts with 30 mM MnCL, for
30 min at 4 C selectively precipitated out the
host nucleic acids leaving the viroids in

Sheath and Grain Discoloration of Rice in
the Philippines. M. T. R. Cerez, M. F. Van
Outryve andT. W. Mew. IRRI.

IRRI initiated a five-year collaborative
research project with the Rijksuniversiteit
Gent (Belgium) funded by the Belgian
Ministry of Foreign Affairs. It aims to
establish the identity of bacterial pathogens
causing sheath and grain discolorations, study
their transmission by seed, and design fast
and reliable detection and identification
methods. Isolation of bacteria from
discolored sheaths and grains collected from
different rice growing areas in the Philippines
showed that out of more than 7,000 isolates,
212 were pathogenic. One hundred and six
were from Ifugao, 35 from Iloilo, 22 from
Laguna, 16 from South Cotabato, 5 each
from Camarines Sur, Isabel and Sultan
Kudarat and 1 each from Albay and Davao
del Norte. Artificial inoculation at seedling
and booting stages with fluorescent/
nonfluorescent and fermentative/oxidative
isolates resulted in varied symptoms.

Survey, Etiology and Control of the 'Bugtok'
Disease of Cooking Bananas. C. E. Soguilon,
M. P. Natural and L. V. Magnaye. BPI,
Davao and UPLB.

Two distinct symptom types of 'bugtok,'
the red and the black, were observed to occur
under natural field conditions. The red
symptom type was observed in Cavite,
Batangas, Quezon, Palawan, Leyte, Samar,
Camiguin Island, Misamis Oriental, South
Cotabato and Agusan del Sur while the black
symptom type was observed in Davao City,
Davao del Norte, Davao del Sur, Davao
Oriental and Bukidnon. It was only in Sultan
Kudarat where no 'bugtok' infection
_:-_l --.I.-:0 _r .--_ -..I 1--I_

did not differ significantly from those of
samples collected from areas where the
disease was not observed. Exudates were
obtained after incubating the diseased
peduncles and male axes for 2-4 weeks. Only
under severe infections were milky exudates
observed from freshly cut male

The colonies of 'bugtok' isolates on
tetrazolium chloride agar medium were
white, irregularly round, convex, fluidal and
with nil to faint pink formazan pigmentation
in helical pattern.

Pathogenicity tests showed that the
'bugtok' isolates could cause wilting of field
grown 'Cavendish' suckers, tomato seedlings
and tissue culture-derived 'Cardaba'
plantlets. Black symptom type of infection
was reproduced upon inoculating the shoots
of tissue culture-derived 'Abuhon' plants.

Initial attempts to control the disease
showed that bagging unopened female
inflorescences of cooking bananas resulted in
the production of healthy bunches.

Results of tests conducted on the
'bugtok' isolates were all indicative that the

January- unae iuw


ADOU&M Ofo Papera

common problem encountered by farmers
Using Rice Crop Parameters to Differentiate since they started farming. Majority of the
Two Upland Sites. E. M. Kuerschner, D. L. farmers, who observed tungro on the main
Pabale and M. J. Bonman. Justus-Leibig crop and IRS var, reported yield losses of
University, Germany and IRRI. >80% and used insecticides to control the
Differences in the occurrence and Many of the farmers owned,a knapsack
severity of rice blast were observed in upland sprayer. Most of the farmers used pesticides
rice sites. Crop growth was affected by site based on their experiences. Pesticides were
properties and, consequently, by the disease, obtained mostly from local pesticide dealers
To determine the effects of selected site- on a cash basis. All respondents, at one point
specific characteristics, we recorded crop or another, used insecticides which were
development (i. e., tillers/ml2, canopy height commonly applied on a calendar basis.
and cover), total dry matter, grain yield, and Herbicides were also commonly used.
yield components (1,000-grain weight, Farmers usually spent P100-500 for
panicles/m filled spikelets/panicle and insecticides and P100-300 for herbicides.
percentage of unfilled spikelets) in two
upland sites (i. e., Sto. Tomas, Batangas and When asked where pests originated,
Cavinti, Laguna) during wet seasons from many of the respondents answered that they
1987 to 1989. These sites differed in their did not know followed by those who stated
edaphoclimatic characteristics but were that weather conditions influenced pest
similar in tiller number during vegetative occurrence. Many farmers claimed pests
growth and number of panicles at harvest could be avoided by applying pesticides even
which were found varying among years. before pests are observed. More than half of
Compared to those in Cavinti sites, higher the respondents believed that certain
canopies and lower canopy cover were varieties had less pests.
observed in the Sto. Tomas site with the site-
year interactions being significant. Among
the yield parameters, total dry matter and
percentage unfilled spikelets showed a site-
year interaction. Higher total dry matter,
grain yield and 1,000-grain weight, and lower
percentage unfilled spikelets were
consistently observed at the Sto. Tomas site
which proved to be relatively fertile.
Relations of crop growth variables and yield,
and possible interactions of crop variables
and blast disease are presented.

Perception on and Management of Pests by
Bulacan, Nueva Ecija and Pampanga
Farmers. F. A. Elazegui, J. Soriano, Jr. and
P. S. Teng. IRRI.

Development of pest management
strategy for farmers' field involves an
understanding not only of the physical and
biological environments but also of the socio-
economic aspect which influences farmers in

In the survey conducted, tungro,
followed by brown planthopper and
stemborer, was identified as the most



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