Front Cover
 Front Matter
 Abstracts of papers presented at...
 Survival of pseudomonas solanecearum...
 Genetic recombination in the blast...
 Survey of pythium associated with...
 Rapid detection of tabacco mosiac...
 Effect of nematicides and tagetes...
 The effect of ammonia and propionic...
 Screening for fusarium wilt and...
 Note: Corynespora disease of papaya...
 Back Matter
 Back Cover

Group Title: Journal of Tropical Plant Pathology
Title: Journal of tropical plant pathology
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00090520/00022
 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: June 1979
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: VID00022
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
    Front Matter
        Front Matter 1
        Front Matter 2
    Abstracts of papers presented at the sixteenth annual meeting of the Philippine phytopathological society inc., Holiday Inn, Metro Manila, 2-5 May, 1979
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
    Survival of pseudomonas solanecearum E.F. Smith in the rhizosphere of some weed and economic plant species
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
    Genetic recombination in the blast pathogen pyricularia oryzae Cav.
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
    Survey of pythium associated with tabacco in the Ilocos region and their comparative virulence to eight varieties of tabacco
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
    Rapid detection of tabacco mosiac virus in orchids
        Page 137
        Page 138
        Page 139
        Page 140
    Effect of nematicides and tagetes erecta on the control of meloidogne incognita and on yield of tomato
        Page 141
        Page 142
        Page 143
        Page 144
    The effect of ammonia and propionic acid on the growth and aflatoxin production of aspergillus parasiticus NRRL 58 35
        Page 145
        Page 146
        Page 147
        Page 148
    Screening for fusarium wilt and dry root rot resistance in cowpeas
        Page 149
        Page 150
        Page 151
        Page 152
        Page 153
        Page 154
        Page 155
        Page 156
        Page 157
    Note: Corynespora disease of papaya in the Philippines
        Page 158
        Page 159
        Page 160
        Page 161
        Page 162
    Back Matter
        Page 163
    Back Cover
        Page 164
        Page 165
Full Text

1WI Ei "H NE D1



A\ E--*.---*._ -X n- -- ^ -- __- -A,,r, J.. C*:-. A-.l ^A-L A ^. --I

May, 1979 .................

Survival of Pseudomonas solanacearum E.F
Rhizosphere of Some Weed and Ecor
Species A.J. Quimio and H. H. Cha

Genetic Recombination in the Blast Pathog
orvzae Cav. K. Manibhushan Rao a

ith in the
c Plant

l.H O u . . . . . . . . . . . .

Varieties ot tobacco Florida U. Puruganan and
Tricita H. Quimio ...................... .................

Rapid Detection of Tobacco Mosaic Virus in Orchids -
L.T. Talens, N. Chansilpa and Angelita D. Talens ..... ...........

Effect of Nematicides and Tagetes erecta on the Control
of M'clh/oidgnc incognita and on Yield of Tomato -
R. G. Davide ................................. .............

The Effect of Ammonia and Propionic Acid on the Growth and Afla-
toxin Production of Aspergill.us para-
siticus NRRL 58 35 Ida F. Dalmacio ............. ...............

Screening for Fusarium Wilt and Dry Root Rot Resistance
in Cowpeas Cynthia L. Dacquel, P.H. Halos.
and H. Aycardo ....................... ....................

NOTE: Corynespora Disease of Papaya in the Philip-

Founded 10 October 1962


easurer LINA L. ILAG
)ard Members: MANUEL K. PALOMAR


nerican Cyanamid Company, Princeton, New Jersey, USA.

iyer Philippines, Inc., 622 Shaw Blvd., Mandaluyong, Metro Manila

inlubang Sugar Estate, Canlubang, Laguna

jo Plantation, Inc., Tagum, Davao del Norte

- -,


Official Organ of the Philippine Phytopathological Society, Inc.


TRICITA H. QUIMIO, Editor-in-Chief, Department of Plant Pathology
UPLB, College, Laguna
S. C. DALMACIO, Associate Editor, UPLB, College, Laguna

2-5 May 19

'ungbean mottle virus. L.T. Talens, I
Dolores-Talens, A.A. Lacuata, and
Martinez (UPLB). I
'ost range and symptomatology. b
gbean mottle virus infected a limit- e
lumber of plant species mainly be- c
ing to Chenopodiaceae and Legumi- 3
ae. Chenopodium amaranticolor c
:e et Reyn. and C. quinoa Willd. devel- i!
I chlorotic lesions which spread sys- N
cally in the latter but not in the n
ler host plant. Cyamopsis tetragono- r;
(L.) Taub., Macroptilium lathy- t,
?s L., Phaseolus acutifolius L., andP. 4
vis L. showed diagnostic local, non- N
smic lesions on inoculated primary or n
ledon leaves. e
lungbean (Vigna radiata (L.) Wil- v
cv. CES-ID 21), soybean (Glycine v
cv. Clark 63), and blackgram (P. 1
go L.) responded to virus infection d
the appearance of mild mosaic, p
)w streaks to mottle symptoms. In b
gbean variety "Pagasa" (CES-ID 21), c
ulated primary leaves mainly pro-
ed randomly-distributed chlorotic r
s which later tended to spread and s
ime necrotic, depending upon envi- e
mental conditions. Later, distinct 1
tie, random yellow spots, and green n
-banding appeared on trifoliate leaves. E
bean developed faint sometimes in- (
spicuous and diffused mottle. Some c
ding lines of blackgram and mung- a
a developed bright yellow streaks a
g the veins followed with marked g
tie reaction. Cowpea (V. unguicula- v
L.) Walp. cvs. Early Ramshom and a


) appeared immune to virus infection.

Purification and Properties. Purified
s preparations which were obtained
clarifying infected mungbean leaf
acts with 10% chloroform and two
es of differential high (100,000 g for
) and low (8,000 g for 15 min) speed
rifugations contained full and empty
metric particles 28-30 nm in diameter.
is suspension exhibited a single immu-
ectrophoretic component which mig-
d toward the anode at pH 8.6 and
ard the cathode at pH values below
The electrophoretic mobility of
V was approximately similar to the
lility of the reference slowly-moving
trophoretic protein of cowpea mosaic
s, with a value of 4.0 x 10"5 cm"2
' in 0.1 M phosphate buffer, pH 7.0.
lunoelectrophoretic analysis of virus at
:rent pH values showed an isoelectric
it at PH 4.5. This value was confirmed
minimum solubility and precipitation
irus kept at this pH value.
'edimentation analysis in 10-50%suc-
and CsCI gradients resulted in a
le centrifugal component with an
nated sedimentation coefficient of
S and a bouyant density of approxi-
ely 1.372 g/cm3, respectively.
:d on the bouyant density value in Cs-
and colorimetric analysis MMV was
ulated to contain 25% ribonucleic
1. Polyacrylamide gel electrophoretic
ysis of sodium dodecyl sulfate-de-
led virus showed one protein subunit
i an estimated molecular weight of
ut 43,700 daltons.

Phillinnmnp Phvtnnathnin

Ultraviolet spectrophotometric anal,
sis of purified virus preparations demon
treated absorbance spectrum typical c
nucleoprotein with a minimum optics
density value at 240 nm and a maximurr
at 260 nm. The absorbance ratios 26
nm/280 nm and maximum were 1.47 an
1.19, respectively, without corrections c
values due to light scattering.
Antisera prepared against the purifie
virus reacted specifically in Ouchterlon:
agar gel diffusion tests with titers c
1:640 to 1:1280. No serological relatior
ships could be found between the viru
and other legume viruses with similar
properties except blackgram mottle viru,
The extinction coefficient (E26%o nrn
cm) was determined to be 50.04. Spec
fic infectivity determinations gave value
ranging from 1.2 x 104 to 4.0 x 104 loc,
lesions per mg virus using Cyamopsi
tetragonoloba as assay host.

III. Effect on growth and yield, ano
sources of resistance. Virus infection o
mungbean at 1 to 3 weeks after seedin
reduced yield ranging from 25-279
Maximum loss occurred when plants bi
came infected 1-2 weeks after seeding
minimum loss, at 3 weeks after seeding
Seed transmission tests suggested lack o
virus perpetuation through seeds harvest
ed from infected mungbean plants at al
stages of development. However, vigo
of plants emerging from infected seed
seemed to be affected.
Four or five breeding lines of selected
germplasms tested appeared to posses
varying degrees of resistance/toleranc
to infection with MMV under greenhouse
The relationship of mungbean mottl
virus with other known legume viruse
and its implications on the mungbeal
improvement program are discussed

Evidence that blackeram mottle anc

mungbean mottle viruses are distinct bu
serologically indistinguishable viruses. L
T. Talens (UPLB).

Comparative studies on the host range
and symptomatology of blackgram mot
tie virus (BGMV) and mungbean mottl
virus (MMV) and reciprocal serologica
tests were undertaken. Both viruses wer
efficiently transmitted by mechanical inc
culation onto test plant species mainly
belonging to the family Leguminosaeae
Both viruses were thermostable (reten
tion of infectivity after heating to 95 (
but not to 100 C) and occurred in higl
concentration in infected plants (reten
tion of infectivity after dilution of crudi
sap to 10-6 but not to 10-7).
The response of virus indicators par
ticularly Chenopodium amaranticolor an<
C. quinoa, Phaseolus vulgaris, and Vigni
mungo, and V. unguiculata suggested tha
BGMV and MMV were distinct vira
entities. Only MMV incited chloroti,
local lesions in C amaranticolor and C
quinoa which later was followed by sys
temic spread in the latter but not in thi
former host plant.
Both viruses induced necrotic loca
lesions on Cyamopsis tetragonoloba
Macroptilium lathyroides, Phaseolu
acutifolius, and P. vulgaris.
Reciprocal serological test in Oucther
lony agar gel plates revealed fusion o
proximal ends of precipitin lines suggest
ing identity in antigenic determinants. I
is suggested that MMV is serologicall)
indistinguishable but biologically distinc
from BGMV.

Cowpea viruses in the Philippines. II
Identification of a yellow strain of cow
pea mosaic virus. L.T. Talens and A.C
Dolores-Talens (UPLB).

Survey and systematic investigations
on the identity of viruses infecting cow

w- i

;racts of Papers

:ies similar to the cucum
pea mosaic virus, based ]
ossessed in vitro and ser
retention of in-
i of crude sap to The
detention of infec- Nicotia
10 min at 65-70 C 10-3, I
-etention of infec- 10 mil
25 C for 5-7 days and afl
ys. for 7 d
y of negatively- Elec
warations of con- partial
;ions revealed iso- tively
y particles 28-30 showed
Ouctherlony agar Dou
linst several refer- plates
isera yielded posi- isometi
only against cow- precipi
um. ber mo
>lant species main- The
enopodiaceae and longing
odium amaranti- Cucurb
developed chlorotic naceae.
systemically and
otic in the former
it plant. Both virus
virus i
as assay and diag- L.T. T
a mosaic viruses in
unguiculata devel- A
mptoms, leaf dis- (TMV)
ion. In some cul- original

ninmf int Ftr.n ntln*t slariacb ha.-

. -* .. - -

rr .


Philippine Phytopatholc

local lesion. Capsicum annuum and C. flexuous rod-shaped virions about 51
frutescens produced faint mosaic with 600 nm in size.
apical necrosis in the latter but not in the Serological identification in Oucht
former host plant. Gomphrena globosa lony agar gel diffusion plate gave posit
produced necrotic local lesions. Petunia precipitin reaction only against referee
hybrida showed small chocolate-brown anti-potato aucuba mosaic virus.
non-systemic lesions. Symptomless infections were obscrv
The properties of the virus in crude in several species of Nicotiana except
sap were as follows: retention of infecti- N. glutinosa where symptoms consist
vity after heating for 10 min at 85-90 C, of diffused chlorotic areas develop
but not at 95 C; retention of infectivity Capsicum annuum developed local lesio
after dilution to 10.4, but not at 10-5; with sunken greyish center and conce
retention of infectivity after storage for tric rings which seemed to spread sys
about 4 months at 25 C. mically. Gomphrena globosa form
Electron microscopy of partially puri- necrotic local lesions. Datura stramoniu
fled virus preparations negatively stained had inconspicuous mosaic sympton
with 2% phosphotungstate revealed rigid Lycopersicon esculentum produce
rod-shaped particles 300-350 nm in size. yellow spotting on mature leaves but n
Virus particles tended to aggregate later- on younger leaves.

antiserum preparations.

Potato viruses in the Philippines. I
Identification of potato aucuba most
virus. L.T. Talens, A.C. Dolores-Talec
& D.A. Luna (UPLB).
Previous studies on the identity
viruses in potato in the Philippines si
gested the occurrence and relatively hi,
incidence of potato viruses X, S, Y ai
potato leaf roll virus. Recently, a vir
causing yellow mosaic symptoms w
isolated from infected leaf and tuber sar
ples obtained from Atok, Benguet Pro
ince and Bukidnon, respectively. It w
identified as a strain of potato aucul
mosaic virus. Identification was based c
symptomatology, morphological featu
of the virus particles, and serologic
Electron microscopy of negative'
stained specimen preparations of partia
ly purified virus suspension reveal

*.. ..Tf lj Ovu, f. lrt.m . 5.

Spores from pure cultures of f
fungal pathogens of rice were used to t
the effect of various fungicides at dif
rent rates on the spore germination
Drops of the spore-fungicide suspl
sions were mounted on glass slides plac
inside moist Petri dishes and incubate
for 24 hours. The effectiveness of I
fungicides was determined based on t
percentage spore germinations after t
24-hr incubation period.
Results indicate 6 fungicides to
very effective in suppressing the sp(
germination of the blast fungus, 16 1
leaf scald, 11 for Cercospora leaf spi
4 for brown spot and 14 for sheath I
fungus pathogens.
Four of the fungicides, i.e. BAS 330:
(82% W.P.), Delsene MX (78% W.P
Dithane M-45 (80% W.P.) and Dacol
2787 (75% W.P.) at the rates of 0.05


,e 1979 Abstracts of Papers 92

% product were very effective in sup- seedbeds. Two weeks after seeding, seed-
ssing the spore germination of the lings were exposed to a uniform heavy
It, leaf scald, Cercospora leaf spot and infective blast condition in the nursery.
ith rot fungus pathogens. Other fungi- Favorable conditions for rapid blast de-
s such as Zinc Omadine (48% disper- velopment and heavy disease pressure
i), Difolatan (50% W.P.), Brestan were provided by covering the plants
% WP.) at 0.05 to 0.1% formulation, with plastic sheets for at least three con-
A49104 (50% W.P.) at 0.05 to 0.24%, secutive nights to maintain prolonged
SCop (54.4%a.i.) at 0.15 to 0.3% and dew period. Lesions were counted at
e 25986 (75% W.P.) at 0.03 to 0.04%, weekly intervals starting 1 week after
e very effective in inhibiting germina- exposure to the source of inoculum.
i of leaf scald, Cercospora leaf spot CGA 49104 (50% W.P.) at the rates of
I the sheath rot fungus spores. 4, 8, 16, 32 and 40 g/kg seeds, PP389
he other che s w h e d JF 5816 (50% W.P.) at 20 to 40 g/kg
The other chemicals which exhibitedercob M (70% W.P.) at 20
,FF,~~., ,,c~ ,C,,,,seeds, and Cercobmn M (70% W.P.) at 20

P"" to 40 g/kg seeds effectively controlled
f% WP at leaf blast. At 8 g/kg seeds, border rows on
ea scald an each side of CGA 49104-treated rows

.... T ...., uj ... were apparently protected from heavy
Y6 E.C.) at 0.05 to 0.1% for blast and
SE at 00 5 to 01% for blast a leaf blast infection. Benlate (50%W.P.) at
ald; RH 2161 (2% E.C. at 0.05 to 40 g/kg seeds, both in dry or slurry form,
3% for leaf scald, Cercospora leaf spot gave fairly good control of leaf blast.
brown spot; Hinosan (50% E.C.) at
5 to 0.1% for blast, leaf scald and Phytotoxic effects of the different
ith rot; Kocide 101 (83% W.P.) at chemicals were also noted. At 16 to 40
5 to 0.l%and M7007 PB20 (20%W.P.) g/kg seeds CGA 49104 exhibited phy-
).0625 to 0.125% for leaf scald and totoxic effects expressed as slight delay
ith rot: and PP389 JF 5816 (50% W. and rwdcied nercentane of seed eermina-

-- VV

ieair oast control mn me Diast nursery, were: rnai-ui (z2% E.u.) at U.23
IR442-2-58, highly susceptible to rice EL-291 (75% W.P.) at 0.035%; Hc
blast, was used as the test variety. Seeds 25986 (75% W.P.) at 0.04%; and Hc
were seeded either in plastic seedboxes 00550 (75% W.P.) at 0.013%. Und4
or in the blast nursery plots. Two weeks heavy infective blast conditions in ti
after seeding, the plants were sprayed blast nursery, Cercobin M, Benlate an
three times at weekly intervals starting PP389 JF5816 showed only moderal
at 2 weeks after seeding with the diffe- degree of leaf blast control.
rent fungicide suspensions using small E o c a
Effect of chemicals against leaf bla
plastic sprayers. The sprayed plants were
immediately exposed to the source of of ce in greenhouse and upland bla
nursery. Y.H. Lee, J.M. Bandong, & J.
inoculum in the blast nursery plots.H. Lee, J.M. Bandong,J.
Naturally-infected leaves cut into short
pieces and spread uniformly on the test Four different methods, i.e. seed, so
plants served as supplemental source of seedling dip and foliar spray app
inoculum in addition to the standing in- cations with systemic and nonsystem
fected plants. The test plants were fungicides were used to select new funj
covered with plastic sheets for at least cides against leaf blast.
three consecutive nights to insure rapid CGA49104 (50% W.P.), F-1 (40% i

counting the number of lesions per see
ling, the first cound made 1 week aft
the first spray application and week
In the first two trials, Benlate (50%1
P.), Hinosan TCP (35% W.P.), PP31
JF5g16 (50% W.P.), and Cercobin I
(70% W.P.), each used at the rate i
0.05% spray, showed effective leaf bla
control even until 3 weeks after the la
or third spray was applied. Hinos;
E.C. (50% E.C.), Delsene MX (78%W.P
Dithane M-45 (80% W.P.), Daconil 27(
(75% W.P.), each at the rates of 0.05
sprays and Top Cop (54.4% a.i.) at 0.3'
showed only a slight to moderate degri
of leaf blast control when compare
with the unsprayed plots.
In another trial where disease develop
ment was very fast and disease press
was very heavy, Hinosan TCP, Hinos;
E.C. and CGA 49104 (50% W.P.), ea<
used at the rate of 0.05% spray, show
the most effective leaf blast contr
among the chemicals tested. Other funj

of 0.5% suspension when used for treat
ing (dipping) the seeds for 12 hr showed
effective leaf blast control.
In soil treatments (either drenched <
soil mixed) with systemic fungicide:
CGA49104G5, (a 5! granular formula
CGA49104G5, (a 5% granular formula
tion), F-l (8% granules) at 40 kg/ha, an
EL-291 at 25 kg/ha (0.5%) were moi
effective than the other chemicals tested
However, CGA49104 showed leaf ti
blighting and EL-291 exhibited sloi
growth of seedlings.
In the seedling dip treatment, CG
49104 (0.1%) was the most effective f
leaf blast control among the chemic,
tested in 12-hr treatment. EL-291 show
very effective leaf blast control at bo
the 30 and 10 min dip treatment
but other chemicals were less effect
even at 30 minutes dipping.
All the chemicals, i.e. CGA49104 (51
W.P.), Hinosan (30% E.C.), Kitazin (41
E.C.), F-l (40% E.C.), Kasugamin (2% ]
C.), Benlate (50% W.P.) applied at tl
t* n 4 _n j .- -. _. 1 J 7T mfll /

DL:l:rr:~r DL..c~lC1rrl~.

I most effective for leaf blast con- suspension, Validacin (3% solution) at

rays. 0.05% were not as effective as Iprodione,
but exhibited effective sheath blight
zical control of leaf sheath blight control compared with the unsprayed
?f rice. J.M. Bandong, B.A. Estra- check plots on three test varieties
Sanchez, & J.P. Crill (IRRI). B9c-Md-3-3, IR 1317-392-1-2 and IR1487.
icide foliar sprays were evaluated 372-1-1.
greenhouse and in the field for In the field, Validacin-sprayed plots of
blight control. Seedlings were IR1317-392-1-2 had more than 1 ton and
n the greenhouse in plastic boxes Iprodione, more than 1.5 tons per hectare
ut 2 weeks and then sprayed yield increase over the unsprayed control.
mes at weekly intervals with the An unusual Helminthosporium leaf
e suspensions. The test plants spot on a rice variety Sekiguchi Asahi
oculated with rice grain culture (B689A1-BK2-2-2-4). J.M. Bandong, S.H.
,haath hl;nht Fn m 1 tI A r ,o

- uwx v-ui--yvu MI. -LV Iiamiojy jIn- JL k JJ), 10 rn, o (ki), 4 irJ), L (krj
fected plants in the field. On the two and 1 (PL). Race group PM-1 which i
breeding lines of IR4915, small brownish, duced resistant reactions to all 12 difl
lesions, typically the same as brown spot rental varieties is included to complex
on field plants started to appear also 5 the total number of races to 4096.
to 6 days after inoculation but did not The races can be numbered with
enlarge to the lesion size on Sekiguchi consulting the computerized table
Asahi indicating that the two lines re-, racesby simply adding the values of tl
acted differently from Sekiguchi Asahi. squares equivalent to each race groi
Measurements of conidia from lesions and assuming that for reaction S the valid
of infected leaves were made and the is 0 and R is 1. Finally, add 1 to the tol
number of cells of each conidium were values of the squares whether the reactic
counted. Most of the conidia collected of the last variety is R to S. For example
from infected leaves were slightly curved if reaction pattern of the varieties to :
and widest about the middle portion isolate is SS S R R R RSRRSR Rit
measuring 22.5-65 x 7.5-12.5 u (with an longs to race PA-494 obtained by addii
average of 43.05 x 9.97 u). The number values of (PD), 128 (PE), 64 (PF),
of conidial cells varied from 4 to 10 with (PG), 8 (PI), 4 (PJ), 1 (PL) and 1. A
an average of 7.64. other way of determining the race nut

numbers of Pyricularia oryzae. F.L
Nuque, S.H. Ou, J.P. Crill, J.M. Bandon
& S.P. Ebron (IRRI).
The system consists of a dichotomou
or binary arrangement of susceptible an
resistant reactions of the different;
varieties. The races are grouped usin
reactions of key varieties as the criterio
with prefix P followed by the capit,
letters A (Kataktara DA-2), B(C15309:
C(Chokoto), D(C025), E(Wagwag), F(Pa
kan-tao), G(Peta, H(Raminad Str. 3'
I(Taichung T.C.W.C.), J(Lacrosse), I

verting hexadecimal values to decin
values or its reverse. The reaction p
tern of the above example is grouped in
4 as SSSR = 0001 = I RRRS = 1110
E; and RRSR = 1101 = D. By looki
at the IE in the vertical column and
at the horizontal column the race
equivalent to 493 + 1 = 494. Since t
first variety is susceptible the race nu
ber is PA-494. The researchers work
on races using Philippine different
varieties, International differentials
any differentials can use any of the abc

tain isolate, automatically this belongs Tomato Viruses in the Philippin
to a PA race regardless of whatever re- I. Properties of a virus infecting toma
action combinations take place in suc- Lycopersicon esculentum Mill. L
ceeding varieties. If Kataktara is resistant Talens & A. C. Dolores-Talens (UPL
to a certain isolate but CI 5309 is sus-
ceptible it is classified in PB group, etc. in a survey of viruses infecting tomato
If all the 11 differentials are resistant to a mechanically transmitted virus isol
an isolate it is categorized as PL group. was obtained which was found to dif
The theoretical race numbers for in properties with those of tobac
each group are 2048 (PA), 1024 (PB), mosaic (TMV) and cucumber mos
C1 f)'1\ 'C1Z IDT11 110 /1Df tA fIDC1 .:..- t11'Xl\ The -.... .; *Ir, ..:,

.1 .

June 1979 Abstracts of Papers 9<

in crude sap were as follows: retenton stations, leaf tissues were sampled al
of infectivity after dilution to 10-3; but random and analyzed for virus by agar-ge
not to 104 ; retention of infectivity after diffusion technique employing reference
heating for 10 min at 60-650C, but not at antisera against several isometric legume
700C; retention of infectivity after viruses. All six samples tested showed
storage at 250C for 3-5 days; but not for positive precipitin reaction against cow
7 days. pea mosaic virus (CPMV) antiserum. Sub
The following virus indicator plant sequent transmission experiments ontc
species were found susceptible to virus: Chenopodium amaranticolor Coste el
Capsicum annuum, Datum stramonium, Reyn. C quinoa Willd, and Gassia obtu.
D. metel, Lycopersicon esculentum cv. sifolia L. resulted in the appearance ol
Marikit, Nicotiana glutinosa, N. cleve- local lesions typical of CPMV infection
landii hybrid, and Petunia hybrida. Serological reaction in agar gel plates
No. local lesions were formed nor was showed that the virus reacted against
virus recovered from Chenopodium ama- CPMV virus antiserum. Electron micros

attributed to the late formation ot uredia ditterent ages suggested that symptom
and uredospores and a shorter duration development was very slow on older
of active uredospore release compared to plants. Senescence of the outer leaves
susceptible TK-5 in which there was was rapid and the midribs became dark
earlier uredial development, earlier release brown while the stalk was gradually
of uredospores and a longer period in rotten. Individual colony types or
which uredia continued to release spores mixture of both showed no difference
before they became senescent. in symptom development.
Inoculation on detached stem by the
Etiology of a bacterial stalk rot of rice. pin-prick method in the laboratory show-
T.W. Mew, M.B. Rosario and K. Tsuchiya ed no difference in rotting between the
(IRRI). two colony types under different tempe-
A bacterial disease of rice causing stalk On PSA, some isolates of Type A were
rot on IR36 and IR29-192 was found in butyrous, while others were fluidal at
IRRI in 1977 and 1978, respectively, The low temperature levels (30, 25 and 20 C);
disease was observed at maximum tillering but at high temperature (35 C), all were
stage. The infected plants showed brown- butyrous. Type B remained unchanged at
ing and watersoaking of the leaf sheath all temperatures.
and the stem tissues at the basal inter- Initial bacteriological studies indicated
nndre arrnmnrniprl h rn mfinto t th fnl .1 .

wo oistmct colony types. une or type
Swas creamy white, raised, circular
o irregular, with undulate margin, and
he surface was rough at high tempera-
ares. On potato sucrose agar (Wakimo-
o's medium), the colonies became yellow
nd produced gas and brown pigment.
he other one or Type B was white, flat,
lizoid with lobate margin. The colonies
f both types were distinct from Erwi-
ia carotovora var. chrysanthemi, the
ausal organism of corn stalk rot.
Pathogenicity tests on intact plants
y syringe injection showed identical
(mptoms as described above. On young
lants (at maximum tillering stage) how-
ver, young leaves wilted rapidly. Other
ifected leaves dried and senesced while
ie stalk was rotten at the site of infec-
on. Subsequently, the affected tiller
ied; however, the new tillers that
merged were apparently healthy.
Artificial inoculation of plants at

)n corn-stem sections, E. carotovora
rar. chrysanthemi produced distinct blue
)igment and caused rotting at high tem-
)eratures (30 and 35 C). With the "rice
talk rot" bacteria, both colony types
showed no blue pigment on the corn
tem sections.

Relationship of root injury to the
'kresek" phase (wilt) of the rice bacte-
ial blight syndrome. B.A. Zaragoza and
'.W. Mew (IRRI).

Inoculation by dipping roots of rice
seedlings, pulled from seedbeds with or
without attendant root injury in bacte-
ial suspension, resulted in severe kresek
ifection. Sowing seeds directly in a seed-
ed infested with the bacteria yielded
minimal percentage of kresek but if roots
f the plants were artificially wounded
resek was produced at a percentage
similar to the transplanted rice seedlings.

1A hk r-r. n- PnPrr.

When the soil of the seedbed was infeste
at different times the highest percentage
of kresek was produced at the tim
closest to transplanting. No kresek wa
observed when the seedbeds were infeste
at time of sowing. Seedlings of 7 day
after sowing raised in adapog seedbed d<
veloped less kresek infestation than seec
lings at the same age from ordinary seec
Culture of healthy and diseased callih
tissues of corn infected by Sclerospor;
philippinensis. O.R. Exconde and E.A
Perez. (UPLB)

Plant tissue culture technique has bee
employed in this study to provide
means for examining the physiologica
cytological and developmental feature
involved in downy mildew disease devel
Healthy and diseased callus tissues o
corn infected with S. philippinensis wa
successfully grown on artificial media
Callus formation in four nutrient medi
showed that Linsmaier and Skoogs RN
media containing 2, 4-D was superior
Plantlets differentiated from infested,
tissues produced downy growth, with
out conidia, at temperature/relative humi
dity of 23 C/97 percent and 28 C/7:
percent for the night and day conditions

Comparative study of rust inoculatio,
methods on two corn varieties. E.E. Dan
lag and A.R. Josue (CMU)

Three methods of inoculating Puccini
polysora namely: dusting, spray, an(
whorl methods were evaluated for thei
effectiveness in inducing rust infection
on two corn varieties.
Results from two trials revealed tha
under Musuan conditions dusting o
uredospores using fine soil dust as carrie:
gave a significant pustule count per plan
10, 15, 20 and 25 days after inoculation

pension gave the next highest mean pu:
lule count in two trials 10, 15, 20, anw
25 days after inoculation. Whorl method
was the least effective method of inocu
lation because of its low pustule coun
per plant.

Production of the perfect stage o
Rhynchosporium oryzae in culture. J. P
Crill, F.L. Nuque, T.V. de Dios and S.P
Ebron (IRRI).
Attempts were made to produce thl
perfect stage by mating single ascospor,
cultures. The single ascospore culture
were grown separately in nutrient solu
tion for 10 days at 25 C in the dark ii
Erlenmeyer flasks. Portions of thi
conidial-mycelial mixtures were asep
tically pipetted into pctri dishes con
training Sach's medium in 1.7% agal
into which sterile leaf sheath pieces ol
1R442 were embedded. The spore-my
celial mixture of four parents was place
equidistantly on opposite sides of the leal
sheath pieces to mate them.
Perithecia were formed as early as 7
and as late as 14 days after the mating
plates were prepared. Fifty-eight of the
96 attempted crosses resulted on the
formation of perithecia suggesting the
fungus was heterothallic in nature.
Two subsequent experiments were
conducted using ascospore isolates grown
singly or in pair on Sach's agar with or
without leaf sheath. Perithecial forma-
tion occurred only on plates with leaf
sheath, indicating that leaf sheath is
necessary for perithecial production. Fur-
thermore, single ascospore isolates pro-
duced perithecia indicating homothal-
Perithecia ranged from 130-250 u in
diameter, (average 180 u). The asci
varied from 34-80 u x 7-11 u (average

I..n 107

hilinnina Phvtnnrthnlnarv

:d by IA (6), IB (5), IC (5), IE (1), IF East Asia. Other races were present perio-
1), IG (1), IH (1), and II-I (1). Thirty dically and races IA-1 and IG-I occurred
)ne races were determined based on the only once in Latin America and South
'hilippine differential reaction, 20 of Asia, respectively.
which are newly identified (PA-509, m n o
'B-212, PB-467, PC-212, PC-467, Induced mutation of Xanthomonas
C-4721, PD-146, PD-147, PD-195, oryzae for virulence and avirulence. K.
'C-471, PD-146, PD-147, PD-195,
'D-196, PD-209, PD-216, PD-245, lsuchiya, T.W. Mew & S. Wakimoto
'D-441, PE-45, PF-19, PI-3, PI-4. PI-8 (IRRI).
Lnd PM-1). The number of races identi- Strains PX061 and PX063, exempli-
ied based on the new Japanese, old fled by Pathotypes 1 and 2, respectively,
lapanese and Korean differentials are were used in inducing mutation for viru-
37, 29 and 17, respectively. The major- lence and avirulence. PX061 infects rice
ty of the races belong to JOC group such as IR8 with no functional genes for
t6) in the old Japanese differential bacterial blight resistance, while PX063
md KA (13) in the Korean differentials. infects IR8 as well as rice with the Xa4
for resistance.
Race patterns of Pyricularia oryzae Mutan n n
Mutation was induced by treating the
n the different rice geographical re- streptomycin-resistant parent strains with
ions of the world. C.Q. Torres, F.L. 50 ppm of N-methyl-N-nitro-N-nitroso-
uque, S.H. Ou, T. T. Ebron Jr. & J. guanidine (NTG) in phosphate survival of
. Cll (IRRI). the total bacterial cells. Based on this
The race pattern of Pyricularia ory- treatment, several mutants were obtained.
,ae in the different geographical re- Pathogenicity of the mutants were
lions of the world where rice is grown then tested on IR8 (40-day-old plants)
vas compiled from International Blast by the leaf-clipping method of inocula-
4ursery results for 13 years using the tion. Subsequently, three distinct types
actions of the International differen- of mutants were identified based on viru-
ial varieties. The race groups detected lence and colony morphology on pep-
n East Asia were IC, ID, IE, IF, IG, tone sucrose agar medium (PSA).
H, and I1 during this period. The most Two mutant strains, PX063-6 NTS and
,-.,1, -..., 1. .^ .1- i-r ITO __.j PYOA?.- NITR uar ri r AvaraA frnm PY.

I -- I .

dune 1iv-n

Abstracts of Papers

or group I, an Isolare conecrea Irom ngn
elevation (ca. 7000 ft) was consistently
less aggressive than others on lesion length
caused at a given time on older plants,
and with a longer incubation period at a
relatively high inoculum level (10" cells/
ml) on IR8.
The variation in lesion was distinct
between the two groups on the differen-
tials but within each grodp, it was conti-

on the three rice differentials IR8, IR36,
and IR1545 as compared to the parent.
The latter was almost identical to the
parent. The colony of PX063-6-NT5 on
PSA was yellow, mucoid and with
smooth margin, while that of PX063-NT8
was white on PSA.
PX061-NT3 was a mutant in another
category. It was avirulent on the rice

spontaneously changed in colony color nuous variation is a distinct character of
on PSA from white to yellow but re- the virulence groups rather than the dif-
mained avirulent. Isolates from plants ference of virulence among the isolates
infected with PX063-6-NT8 was virulent of the groups.
with white colony on PSA.
Efficacy of three protectant fungicides
The growth of PX063-6-NT8 was no for control of downy mildew of corn.
diffirpnt frnm that of the narpnt strain .-

Philippine Phytopathology

Comparative effect of different nema-
ticides for the control of nematodes
attacking bananas. N.I. Roperos & I.D.
Lozano (Twin Rivers).

The effectiveness of four nematicides
namely: Mocap 10G, Furadan 3G, Nema-
cur 5G and Nemagon 75 E.C. using the
concentration recommended by the man-
ufacturers were tested for the control of
nematodes attacking Giant Cavendish
bananas. Among the nematicides used,
Nemagon 75 E.C. (1,2-dibromo-3chloro-
propane) at 40 ml/mat followed by
Mocap 10G (0-Ehyi S,S-dipropyl phos-
phorodithicate) at 60 g/mat were-found
markedly effective against banana nema-
todes. No phytotoxic effect was noted
on the treated plants during the three
years of observations.

Plants treated with Mocap 10G and
Nemagon 75 E.C. had reduced nematode
population level particularly the burrow-
ing nematode, Radophulus similis. Their
reduction in number gave an apparent in-
crease in bunch weight during the last
phase of nematicide application. Furadan
3G and Nemacur 5G applied at 75 g and
80 g/mat, respectively, did not increase
bunch weight at the time the experiment
was terminated.
Screening methods for sheath rot of
rice. B.A. Estrada, L.M. Sanchez & J.P.
Crill (IRRI).
Attempts were made to identify re-
sistant cultivars by evaluating various
screening methods for the disease. A
pathogenicity test was first conducted in
the screenhouse using the susceptible rice
line IR1487-1-1. Plants were grown in
30-cm diameter pots and inoculated
with 2-week old inoculum by inserting
single grain culture 1-2 cm deep between
the leaf sheath and stem. Inoculation of
62-day old plants provided an effective

test of pathogenicity, with 93% of the ino-
culated tillers showing infection. Typical
symptoms of the disease appeared 5 days
after inoculation and severe rotting of
leaf sheath at the point of inoculation
occurred shortly thereafter. In another
trial, grain insertion on 50-day old
plants showed even a higher percentage
infection, with 97% of the inoculated leaf
sheath infected.
A comparison of the grain insertion
method, injection of spore suspension
and spraying spore suspension at different
growth stages (20, 37, 52 and 67(DT)
days after transplanting) indicated spray-
ing was not an effective inoculation tech-
nique. Single grain insertion resulted in
38, 0, 80.0, 89.7 and 72.4% infection on
tillers inoculated at 20, 37, 52 and 67
DT, respectively, while injecting spore
suspension showed the respective percent-
age infection of 100, 90.9, 10.8 and 81.
3%. No lesions were observed in spraying
spore suspension at any stage of growth.
For screening, grain insertion at about 52
DT seemed to be the best. Although high-
er percentage infection was obtained by
injection at 20 and 37 DT, symptoms
produced consisted only of typical
lesions (narrow dark brown stripes). In-
jection at 67 DT or booting stage appear-
ed to be the most appropriate method
and right stage for evaluating yield loss,
with some panicles from inoculated tillers
unable to emerge.
A screening method for testing varietal
resistance to ragged stunt in greenhouse.
K. C. Ling and G. Z. Salamat, Jr. (IRRI)
A method for testing varietal resist-
ance to ragged stunt disease, transmitted
by the brown planthopper Nilaparvata
lugens, in the greenhouse was developed.
The method consisted of 1) rearing and
propagating the brown planthoppers in
screen cages; 2) making the insects viru-
liferous by providing the insects with

Vol. 15

seasea nce plant at nympnai stages; iyangaia snowed percentages of infec-
Id the insects used for inocula- tion in between that Ptb 21 and TNI.
)n 9 to 10 days after acquisition feed- However, the percentage of infection of
g; 3) preparing test seedlings of rice WC1240 was lower than that of Gangala.
rieties or lines in pots at 29 seedlings/ The average life spans of the brown
it; 4) inoculating the seedlings at 13 planthoppers on Ptb 21 and Gangala
15 days after sowing in inoculation were shorter than those on WC 1240
ges with 6 to 8 insects/seedling for an and TNI. However, no significant diffe-
oculation access time of 24 hours, and rence in the life span was obtained either
examining and counting the infected between Ptb 21 and Gangala and between
edlings after the latent period. The per- WC1240 and TNI. Hence, Ptb 21 was re-
ntage of infected seedlings was used as sistant to both the ragged stunt disease
criterion for determining the degree of and to the brown planthopper. WC1240
distance: 0 to 30% infection, resistant; was more resistant to ragged stunt than
to 60%, infection, intermediate; and 61 Gangala but more susceptible to the
100% infection, susceptible. The brown planthopper than Gangala: and
method had a capacity of inoculating TNI was susceptible to both the ragged
!8 seedlings in 32 pots in two inocula- stunt and the brown planthopper. Con-
)n cages in a day. Of 4,641 entries of sequently, varietal resistance to the
:e varieties and lines tested from May to ragged stunt disease is not always asso-
:cember 1978, 2, 16 and 81% were ciated with varietal resistance to the vec-
tegorized in resistant, intermediate, and tor.
sceptible groups, respectively. Varieties Evaluation of different resistance to
the resistant group will be retested bacterial blight of rice. T.W. Mew, C.M.
r the confirmation of their resistance Vera Cruz and R.C. Reyes (IRRI).
the ragged stunt disease.
Provinllce etcll inmrlletar "hat" r+d1et.

Four rice varieties were tested for their
distance to ragged stunt disease, trans-
:ted by the brown planthopper Nila-
vata lugens, by comparing seedling in-
tion after inoculation with viruliferous
ects in screened cages at four to six in-
ts/seedling and from 358 to 437 seed-
gs/variety. The resistance of these varie-
i to the brown planthopper was also
ted by comparing the average life span
the insects confined on seedlings in test
)es at 200 insects/variety. Ptb 21 (IRRI
:. no. 11053 from the Central Rice Re-
rch Institute, India) consistently show-
a low percentage of infection. Tai-
ing Native 1 (TNI) showed a high
rcentage of infection. WC1240 and

o tour major groups namely: overau
instance which denotes a resistant reac-
n to a specific pathotype at all stages
plant growth, adult plant resistance
ach denotes a resistant reaction at the
ult plant stage based on the infection
flag leaves but not at the seedling
ge, moderate resistance and partial
distance which denote intermediate
ease reaction, and unstable and
hanging according to locality and some-
ies season of testing.
Overall resistance was further found
t to be affected by increasing nitro-
i level unless the resistance was over-
me by pathotypes with specific viru-
Ice. The infection at tillering stages
5 DAS) of plants with adult plant re-

.Philippine Phytopath(

distance was not ntterent trom tmo
with no resistance. The increase in lesic
length on plants with intermediate r
action to bacterial blight was consider
ably less than those with no resistance
Rice with adult plant resistance shoi
ed significantly shorter lesions when i
fection occurred in older plants. Ri(
with overall resistance showed no dra
tic difference in disease reaction
three ages, 40, 60 and 80 days after soi
ing. When a plant with overall resistan(
was overcome by pathotype with spec
fic virulence, the disease reaction change
from resistant to susceptible at all stage
At low inoculum level plants wil
adult plant resistance inoculated at tille
ing stage produced lesions as long as tho
with no resistance but considerable
longer than rice with intermediate resist
ance. Plant with overall resistance show<
negative infection at low inoculum lev
but positive infection with shorter lesiol
at high inoculum level.
Screening for resistance to Helmi
thosporium leaf spot of sorghum. S.,
Dalmacio, C.B. Pascual & P. Javi
Five hundred and fifteen sorghu:
-materials representing locally availab
varieties, advanced generation lines ar
introduced germplasm materials we
screened for resistance to Helminthosp,
rium sorghicola during the 1978-19
dry season planting using artificial inoc
lation. Inoculum was prepared by groom
ing the fungus at room temperature c
sterilized sorghum grains in flasks which
were shaken every other day to attain
even distribution of the fungus. Contel
of the flasks were then mixed together
after 7 days of incubation and air-drie,
Inoculation was done by placing 10-2
infested grains into the whorl of sorghul
plants prior to booting stage. Resistant
was evaluated 10 days later using a ratir

aL,41i UI .1J Wl.ii, a U nIUiLa 1Lll I a
ance and characterized by minute, chlor
tic or necrotic flecks, and 5 denotes su
ceptible reaction characterized by tl
presence of typical lesions.
None of the recommended varieti
tested showed resistance while only tv
of the 157 advanced generation lin
(CS-lines) tested consistently showed i
distance (scale 1-2). Sixty nine of 3:
introduced materials tested consistent
showed resistance, although the resistant
of other lines has yet to be confirm

A study on some components ofresi,
ance to rice blast. L. K. Chou, F.
Nuque and J.P. Crill (IRRI)
Resistance of cultivars Tetep, Carreo
IR36, IR442-2-58 and KTH-17 inocul
ed with isolates 1-2017 and 1750678-1
4-5 leaf stage incubated in the 3 SA
cabinet (25 C/21 C) was determined usil
number, size of lesions and spores pr
duced on the lesions of each variety
The general reactions of the varieti
were recorded 6 days after inoculation
Carreon was resistant to both isolate
while KTH 17 and IR442-2-58 were su
ceptible to 1-2017. IR36 reaction to bol
isolates was the reverse of Tetep. Cull
vars Tetep, IR36 and IR442-2-58 exhibi
ed considerable fewer number of lesioi
than KTH. The size of lesions produce
also differred greatly between the tw
isolates on the same variety. On KTH-l'
lesion size induced by 1-750678-1 we
twice (16.8 x 2 mm) those produced b
1-2017 (8.1 x 2 mn) 15 days after inoci
lation suggesting that 1-750678-1 w;
more virulent than 1-2017. Twenty foi
days after inoculation little difference i
lesion size of the two isolates on KT]
was observed. The spore number (
1-750678-1 from KTH lesion was coi
siderably higher, ranging from 100 t
5,900 spores compared to 1-2017 (1(


Abstracts of Papers

1800) during the sporulation period. Re-
sults further indicated that 1-750678-1
was more virulent than 1-2017.

Leaf wettability and stable resistance
to rice blast. S. Suryanarayan and J.P.
Crill (IRRI)

Although horizontal resistance to rice
blast has not been demonstrated in the
true sense of the term, varieties like Tetep
and Carreon show a type of stable resist-
ance. Only a few lesions of any type de-
velop on them. It seems useful to under-
stand why few lesions develop on these
varieties in the context of breeding for
blast resistance of either type.
The number of lesions that develop
on the rice plant has been well correla-
ted with the number of conidia deposit-
ed on the leaf. Since the rice leaf is very
hydrophobic, it is conceivable that the
distribution of conidia on the leaf surface
could be affected by its wettability. De-
position of conidia of the blast fungus by
a leaf dip inoculation technique showed
that lesser number of conidia were
trapped per unit area of the leaf surface
of the blast-resistant than the susceptible
cultivars. Leaf samples collected from an
upland blast screening nursery also show-
ed lesser number of conidia deposited per
unit area of the leaf in the resistant Car-
reon or Tetep than in the susceptible
IR442. Assessment of the wettability of
the blast-resistant (Carreon, Tetep, IR36)
and susceptible (KTH, IR442) rice leaves
indicated that the former were wetted
to a lesser extent than the latter. A study
of the epicuticular wax content further
showed that blast-resistant Tetep had a
higher wax content per unit area of the
leaf than the susceptible KTH. These re-
sults suggest that the fewer number of
lesions on varieties like Carreon and
Tetep may be associated with the relative
wettability of their leaf surfaces. The
implication of these observations in

breeding for stable resistance to rice
blast is discussed.
Test of different fungicides for the
control of late blight of potato. J.S.
Mariano (BPI)
The efficacy of different fungicides
for the control of potato late blight (Phy-
tophthora infestans) was evaluated in
farmers field at La Trinidad, Benguet
from November 1978 to February 1979.
Spraying was done when plants were
about 10-15 cm. in height at 1 week
intervals with a total of 8 spraying during
the crop season.
Curzate M appeared highly effective
and gave significant control over Difola-
tan 4F, Zincolfol and Captafol at 1 per
cent level of significance. Daconil,
Dithane M-45 and Manzate 200 consist-
ently gave statistically similar results and
were significantly better than Difolatan,
Zincofol and Captafol. However, the
latter gave highly significant difference
over the control. All the treatments show-
ed highly significant yield difference over
the unsprayed.

Survival of sheath rot and leaf scald
pathogens in rice seeds. L.M. Sanchez,
BA. Estrada, FL. Nuque and J.P. Crill

The survival ofAcrocylindrium oryzae
and Rhynchosporium oryzae, the organ-
isms causing sheath rot and leaf scald
diseases of rice, respectively on rice seeds,
was determined by plating, blotter and
centrifuge methods.

Results of the laboratory tests indi-
cated that both organisms were present
in either or both the air-and-sun-dried
samples stored at 20, 25, 30 and 35 C
for up to 12 weeks. Seedlings infected
with either pathogen were transplant-
ed in pots in the greenhouse for observa-
tion up to maturity. The presence of the

June 1979

Umvi uMuiI uwiu n%,uI w U Iuum uum. vjuic crown planuioppers snoweu negauv r1v
associated organisms such as species of suits, suggesting that the two weeds wen
Fusarium, richoconis, Urvularia, not host of rice ragged stunt virus.
Nigrospora, Helminthosporium, Phoma, R
Response of improved mungbear
Cercospora and other unidentified, non-
Sa varieties to different levels of inoculun
sporulating, slow-growing fungi, were con o Cm
concentration of Colletotrichum lindi
also observed during the tests.
muthianum. R.D. Magallon and N.S.
The study is still in progress and will Franje (CMU
Franje (CMU)
continue for a period of 6 months or
until the time that both organisms can MG 50-10A, CES 35, CES 14, anc
no longer be detected. ARV 20 were the varieties used in the

Studies on the host range of rice experiment. Among the five varieties onlb
ragged stunt virus. E.R. Tiongco, P.Q. ARV 20 reacted as moderately resistant
Cabauatan, and K.C. Ling (IRRI). CES 14, though susceptible to anthrac
nose gave the highest average grain yieli
The search for additional hosts of the of 180.37 g per plot of sq. m at vary
rice ragged stunt virus, involving species ing inoculum level. CES 35 gave the leas
of Oryza, maize, sorghum and two species average yield with only 77.78 g/plot
of weeds was conducted. Decrease of functional leaf area, pre
Following the cage method of inocu- mature drying of leaves and pod abortion
lation, more than 90% rice ragged stunt caused the reduction in yield.
infection was recorded in Oryza barthii The control plants (not inoculated
(IRRI ace. no. 100122), 0. glaberrima gave the highest average number o
(acc. nos. 100132, 100133, 100152, pods/plant, number of seeds per pods
intMICr IfnCO inCQ CC 10nnC1 / nlant hainht nrl )rain iile./nlnAt ,.,h;l,

showed about 20% infection. None ou
of a total of 41 seedlings of 0. austn
liensis (ace. nos. 100410, 101144, an
101397) became infected after inoculb
tion. Of the 18 maize (Hawaii Supel
sweet No. 9) and sorghum (Cosor 3
plants inoculated with viruliferous brow
planthopper Nilaparvata lugens, none b4
came infected when the insects lived fc
only 3 days on both plant species.
Two different weeds, Echinochlo
glabrescens and Sorghum halepense shom
ing symptoms resembling those of ric
ragged stunt disease were collected an
used as virus source for transmission
study. No positive transmission on Ta
chung Native, 1 rice seedlings from thes
weeds was obtained. Furthermore, inoci

airecuy proporuonat to me mocuiur
Rust incidence on soybean (Glycin
max fL.) Merr. as affected by varyin,
levels of NPK applied singly and in con
bination. V.L. Piccio and N.S. Franj
Nitrogen, phosphorus and potassiur
were applied singly and in combination
to rust susceptible soybean variety (Clar
63) at levels of 30, 60 and 90 kilogram
per hectare. Disease rating based on th
International Working Group for Soybea
Rust rating system was done at fou
stages of plant development: pod forms
tion stage, early pod filling stage, mic
pod filling stage and at late pod filling

tion were translate m terms or yiciu,
pods per plant, seeds per pod, and weight
of one hundred seeds.
Of the 16 treatments, only the plants
given complete fertilizer at the rate of 30
kg/ha gave moderately resistant reaction
to the disease incited by the fungus, Pha-
kopsora pachyrizi Syd. Complete ferti-
lizer application at 90 kg/ha gave the
highest number of pods per plant, seeds
per pod, weight of hundred seeds and
yield per plot. However, plants given this
treatment reacted moderately susceptible
towards soybean rust. This experiment
showed that excess of nutrients increases
the susceptibility of plants to disease.
The effect of varying rust intensity on
the net assimilation rate and yield of two
corn varieties. L.U. Falcon & A.R. Josue
The effects of varying levels of rust in-
tensity on the net assimilation rate
(NAR) and dry grain yield of two corn
varieties DMR Comp. 1 and 2, were deter-
mined during the dry season of 1977
under field conditions.
Results showed that the different
levels of rust intensity attained by adjust-
ing the inoculum density during the
inoculation have no significant effect on
the dry grain yield of the two varieties.
Under the conditions of the experiment,
DMR Comp. 1 gave a relatively higher
yield than DMR Comp. 2.
Analysis also showed that the net assi-
milation rate was not significantly affect-
ed by the various rust intensity 47-67
days after emergence. There was how-
ever, a significant difference between
varieties with DMR Comp. 2 having a
higher net assimilation rate compared to
DMR Comp. 1.
Efficacy of surfactants in smut inocu-
lation. F.T. Gargantiel and F.C. Barredo

varying rates, were tesieu iomr ueir Icwi
in smut inoculation. The VMC standard
inoculation method of 2.5 g spores mixed
in one liter water served as the control.
Percentage infection of more than 50%
was obtained after 180 days when Tergi-
tol NPX and Citowett at 250 and 500
ppm and Surfac H at 100 ppm were add-
ed to the spore suspension. The dif-
ference in the percentage infection com-
pared to the control was highly signifi-
cant. Not one among the wetting agents
tested showed any effects on germ tube
initiation of the spores.
The use thiabendazole in the control
of damping-off in tobacco seedbed.
A.C. Necesito & P. Sta. Cruz (UPLB)
Greenhouse experiment was conduct-
ed to determine the effectiveness of
Thiabendazole (TECTO) in three
methods and concentrations together
with Maneb 80 and Methyl Bromide steri-
lization for the control of damping-off
in tobacco.
Thiabendazole applied as drench at a
concentration of 25 g/50 m2/ 10 1 gave
the highest seedling survival.
The combined drenching (5 mg/50
m2/20 li) and spraying of TECTO (25
g/50 m2/20 1) produced the highest
seedling density of 275 seedlings per
468 cm2, followed by drenching with
TECTO 25 g/50 m2/20 1 concentra-
tion. The average number of seedling
established with drenching, however, was
significantly higher also compared to
spraying alone and/or to drenching plus
spraying treatment.
In pricked seedlings, all treatments
showed no significant effect including
vigor as measured by the number of
leaves, length of shoot, fresh weight and
dry weight of shoot and fresh weight of
roots. Dry weight of roots was higher in
the drenched treatment.

Effect of vesicular-arbuscular mycor-
rhizae on the growth of tomato plants
and their infection by Pseudomonas
solanacearum. P.M. Halos and R.A.
Zorilla (UPLB)
Two-week old tomato (Lycopersicon
esculentum Mill.) seedlings were trans-
planted on sterilized and non-sterilized
soils in no. 6 pots. The treatments were:
inoculation with mycorrhizae, with
mycorrhizal and Pseudomonas solana-
cearum EFS, P. solanacearum only, and
the uninoculated (control) with 15
replicates for each treatment in both soil
Significant differences were obtained
between plants grown in sterilized and
non-sterilized soils in most of the indi-
cated treatments in terms of their mean
final heights, dry weights, percentages of
bacterial wilt infection and with yields.
Tomato plants grown in sterilized soil
and inoculated with mycorrhizae were
taller and healthier than plants of any
other treatments. Those inoculated with
both mycorrhizae and P. solanacearum
grew faster than uninoculated control
plants and those inoculated with P. sola-
nacearum only. Tomato seedlings grown in
non-sterilized soil with corresponding
treatments responded similarly, Those
inoculated with P. solanacearum in non-
sterilized and sterilized soils exhibited
yellowing, stunted growth and wilting.
Decreased incidence of bacterial wilt in-
fection was observed among tomato
plants inoculated with mycorrhizae, then
P. solanacearum in sterilized soil. Possib-
ly, mycorrhizae acted as competitors and
provided mechanical and chemical
barriers against the bacterial wilt patho-
Highest yield of tomato fruits was
observed among tomato plants inocula-
ted with mycorrhizae only in sterilized
.,1 J1.,1 U~l..~ .r 4l*M :n nrlnn a^ n4+l.

both mycorrhizae and bacterium, their
those inoculated with bacterium only
Tomato plants grown in non-sterilizei
soil with corresponding treatments show
ed poorer yields than those grown ii
sterilized soil.

both mycorrhizae and bacterium, the1
those inoculated with bacterium only
Tomato plants grown in non-sterftizeq
soft with corresponding treatments show
ed poorer yields than those grown h
sterilized soft.

une 1979



Respectively, Assistant Professor, Department of Plant Pathology, University of
;he Philippines at Los Banos, College, Laguna, and Crop Protection specialist, Crop Pro-
tection Services, Department of Agriculture, Kuala Lumpur, Malaysia.

Portion of the junior author's M.S. thesis.

Research supported by the Southeast Asian Regional Center for Graduate Study
and Research in Agriculture, College, Laguna, Philippines.


The population of P. solanacearum gradually declined in both rhizo-
sphere and non-rhizosphere soils of jungle rice (Echinochloa colonum L.)
goose-grass (Eleusine indica L.) spiny amaranth (Amaranthus spinosus L.),
corn (Zea mays L.), mungbean (Vigna radiata L.) and rice (Oryza sativa
L.) but not in the rhizosphere soil of common purslane Portulaca olcea
L.) where it gradually but distinctly increased. The rate of population decline
was lowest in P. oleracea, E. colonum, and E. indica, while relatively greater
suppression of the population occurred in rice and corn. Latent infection
by the bacterium was found in P. olemcamn ut not in the other plant species.

The population of P. solanacearum was also higher in the rhizosphere
soil than in non-rhizosphere soil of the weeds. On the other hand, both corn
and rice had relatively higher population in non-rhizosphere soil. In bare
fallow soil, population decline was slow and comparable to that in the weeds.

In bioassays with wilt susceptible tomato cv. 'Yellow Plum', the highest
level of wilting occurred in soil previously planted to common puralane and
the lowest in soils previously planted to corn and rice. Compared to previous-
ly fallowed soil, significant lowering in degree of wilting was detected in soils
previously planted to corn, rice and spiny amarauth, but not in those pre-
viously planted to goose-grass, jungle rice and common purslane.

As different plants exert rhizosphere have the unique ability to survive in the
effects which vary in magnitude, the pre- soil in the absence of host plants, includ-
sence of a particular plant species will ing both crop and weed plants. There is a
greatly determine the survival and per- possibility that P. solanacearum and other
sistence of soil-borne pathogens like P. soil-borne pathogens may persist in this
solanacearum. In many cases, carry- manner. For example, Schroth and Hen-
over of this pathogen has been attribut- drix (1962) discovered that the number
ed to indigenous or native weed flora of propagules of Fusarium solani var.
which could play the role of alternate phaseoli increased in the rhizosphere of
hosts (Kelman, 1953; Dukes et al., 1965a tomato, lettuce and corn, but decreased
and b; Sequeira and Averre, 1961). in the rhizosphere of onion. Valleu et al.
It is also known that some pathogens (1944) had earlier indicated that Pseu-

"- fr "

domonas rabaci and P. angulatum grew
on roots of several plant species unrelated
to tobacco, i.e., henbit, chick weed,
clover and rye. Okabe (1971) in examin-
ing weed rhizosphere soil found that
growth of P. solanacearum was high in
Capsella soil while the bacterium's popu-
lation became very low in Stellaria and
Poa soils after incubation at 30 C for
5 to 30 days.

Thus, the study conducted was aimed
at monitoring the population changes of
P. solanacearum in the rhizosphere of
some plant species found commonly
associated with tomato cultivation, either
as weed or as rotation crop. A better un-
derstanding of how these plants con-
tribute to the survival of the bacterium
would add considerably towards an integ-
rated approach of controlling the bacte-
rial wilt problems.


Top soil from fields previously
planted to vegetables and field legumes,
was collected, thoroughly mixed and
placed into half-drums (44 gal capacity)
which served as microplots. The soil in
each drum was infested with P. solana-
cearum (Isolate LE-13) by pouring the
bacterial suspension around the base of
wilt susceptible tomato cv. 'Yellow
Plum' seedlings. After the plants wilted
md died, the soil from all the drums were
:omposited, mixed thoroughly, and put
back into the drums; 'Yellow Plum'
seedlings were planted into the soil to
:heck infestation with P. solanacearum.

When the second batch of tomato
plants died, the soil in the drums were
planted to several plant species which
included jungle rice (Echinochloa colo-
ium L.), goosegrass (Eleusine indica L.)

L.), common purslane (Portulaca ole-
racea L.), mungbean (Vigna radiata L.),
rice (Oryza sativa L.), and corn' (Zea
mays L.). The first four plants species
are weeds found commonly associated
with tomato growing areas and the
latter three plant species are crops rotated
with tomato in the Philippines. Half-
drums with soil kept bare fallow were
provided as control plots.
Before planting of the test plants,
initial population of P. solanacearum in
the soil in each plot was determined in
the following manner: five soil cores
up to 15-cm depth were taken and
composite. From the composite, one
30-g sample was placed into a sterile
graduated Erlenmeyer flask and sterile
distilled water was added until the 250
ml mark was reached. After shaking for
30 min, a 10-ml aliquot was transferred
to 90 ml sterile distilled water in a flat
bottle. After subsequent transfers of 10-
ml aliquots to 90 ml sterile water, soil
suspensions up to 10"s dilutions were
obtained. Two-tenths ml of 10'3, 104
and 10'5 dilutions were surface-plated
onto Nesmith-Jenkins' (1976) medium
which had been shown to be highly suit-
ed for quantitative detection of P. sola-
aceamm in Philippine soils (Chan and
Quimio, 1978). The plates were incubat-
ed at 30 C for 72 hr after which counts of
P. solanacearum colonies were made
based on the colony characteristics of
he bacterium on the medium on Nes-
nith-Jenkins' medium, P. solanacearum
producess very fluidal round 2-to 3-mm
diameter colonies with bright red dif-
'used formazon centers and narrow white
nargins (Fig. 1).

Beginning at 3 weeks after planting
)f the test species, weekly sampling of
hizosphere and non-rhizosphere soils of
he plants was conducted until the 9th

P. solanacearum in the non-rhizosphere amount of rhizosphere soil used, 33.3
il was similar to that for population ml aliquots of the initial suspension were
termination in the soil before planting; placed into previously weighed petri
e non-rhizosphere soil being taken from dishes and oven dried for 24 hr.
:as devoid of plant roots.
Nine weeks after planting, a bioassay
In determining the population of for bacterial wilt was conducted using
solanacearum in the rhizosphere 4-week old wilt susceptible tomato cv.
il, blocks of soil containing the test 'Yellow Plum' as indicator plants; forty
ints were carefully loosened. Soil to 60 seedlings were planted in each
11 adhering to the roots was considered drum and counts of wilted and dead
rhizosphere soil (Johnson and Curl, plants were made throughout a 21-day
72). The roots with adhering soil were period.
-n washed for 1 min in sterile water in
0-ml capacity flasks. Sterile water was RESULTS AND DISCUSSION
ded to make a 100 ml suspension.
ter stirring with a magnetic stirrer The initial population of P. solana-
ab-line Instruments Inc. Chicago, Ill. cearum in infested soils before planting
S.A.) for 30 min, the suspension was the test plants was not significantly dif-
rially diluted and surface plated in the ferent from each other (Table 1).
me manner as that for the non-rhizo- Sampling after planting indicated, how-
here soil. ever, that there were differences in popu-
lation decline of the bacterium depending
For each composite soil sample used, on the plant species growing in the soil
e moisture content was determined by (Table 2; Fig. 2).
acing 5-to 10-g samples in previously
sighed bags into a hot air oven over- At the 9th week, the population level
ght and reweighed. To determine the of P. solanacearum in the soil were sig-


Philippine Phytopathology

Table 1. Initial soil population of Pseud
plants were planted into half-drum mi

Species to be planted

Echinochloa colonum
Eleusine indica
Portulaca oleracea
Amaranthus spinosus
Zea mays
Vigna radiata
Oryza sativa
Bare fallow (Control)

Grand Mean

a Average of three plates: serially diluted s
kins' medium; colony counts made after

nificantly different from each other
(Table 3). Soils planted with common
purslane, goosegrass, jungle rice, and
mungbean had higher population levels of
P. solanacearum compared to bare fallow
soil and soils planted to rice and corn.
The two latter crops significantly reduced
the population of P. solanacearum
compared to the other plant species.

There was a general decline in soil
population for both rhizosphere and non-
rhizosphere soils except for the rhizo-
sphere soil of P. oleracea which showed
an increase in population level of P. sola-
nacearum with time (Figs. 3 to 6).

The rate of decline in P. solanacearum
population in the rhizosphere and non-
rhizosphere soil of each plant species

lonas solanacearum before weed and crop

P. solanacearum cells
(X 10 )/g soila



suspensions were plated on Nesmith-Jen-
hours of incubation at 30 C.

cea, and A. spinosus) and mungbean
seemed to favor a relatively higher popu-
lation of P. solanacearum than non-rhizo-
sphere soil. The R/S ratio (rhizosphere
population: non-rhizosphere population)
increased with time for these plant spe-
cies while that for corn and rice decreas-
ed. The rate of population decline of the
bacterium in the rhizospheres of the weed
species and mungbean is much more gra-
dual than in non-rhizosphere soils. This
indicates strongly that the rhizospheres of
these plants are favorable for the survival
of the pathogen in the soil.

With corn and rice (Figs. 5 and 6), the
rhizosphere population after 9 weeks was

s the logo population, is the logo UL paV a.u. L ua. .n-
nitial population, x is the timein weeks, cates a less favorable site for survival of the
md b is the rate of decline. organism in the rhizosphere of the said
plant species and thus could bear account
The rhizosphere soil 6f the four weed for the decline of the population of the
species (E. colonum, E. indica, P. olera- bacterium in the soil.

Vol. 15

Survival of Pseudomonas solanacearum

Amongst the non-rhizosphere soils of
the four weed species examined, the
population of P. solanacearum decreased
at the slowest rate in P. oleracea. This can
probably be attributed to the fact that
the rhizosphere population in this weed

species kept increasing with time. Favor-
able conditions for multiplication in its
rhizosphere may be present, allowing the
bacterium to persist in the surrounding
soils for a longer period of time com-
pared to the other plants tested.

Table 2. Changes in population of Pseudomonas solanacearum in rhizosphere and non-
rhizosphere sols of several plant species at different periods after planting

Soil plpted No. P. solanacearum cells (X 106 )/g oil
Owk 3wk 3wk 4wk 5 wk 6 wk 7 wk 8wk 9wk




4.34 13.32 8.30
9.62 8.03 5.44
0.47 1.66 1.53

8.53 16.65 6.56
7.27 8.19 6.21
1.17 2.03 1.06

9.55 25.26 11.60
8.32 9.58 7.08
1.46 2.63 1.64

9.95 61.18 8.96 5.76
9.13 6.80 3.73 4.05
1.09 0.91 2.40 1.42

3.30 6.41 4.67 2.19
3.08 2.44 2.91 11.19
1.07 2.63 1.60 1.84

2.67 8.18 6.57 2.67
6.98 6.67 5.08 2.81
0.38 1.23 1.29 0.95

2.05 3.69 1.05 0.46
3.56 3.55 2.28 1.09
0.58 1.04 0.46 0.45

E. colonum
E. indica
P. oleracea
A. spinosus
Z. mays
V. radiata
0. sativa
Bare fallow

6.51 4.68 8.24
3.90 2.35 3.08
1.67 1.99 2.68

6.01 4.44 5.46
4.29 2.37 3.56
1.40 1.87 1.53

27.72 45.60 17.11
5.08 3.08 5.39
5.46 14.80 3.174

4.63 3.28 2.79
3.63 3.20 2.04
1.28 1.03 1.37

0.95 0.81 0.83b.
1.35 1.15 1.2
0.70 0.70 0.61

3.35 6.40 4.63
2.56 2.30 2.68
1.31 2.78 1.73

0.37 0.49 0.35~
0.59 0.15 0.82
0.63 3.20 0.421

1.58 2.50 2.11

a Average of three plates; serially diluted soil suspensions were plated on Nesmith-
Jenskins' medium; colony counts made after 72 hours of incubation at 30 C

bR -- Rhizosphere aoil
S Non-rhizosphere soil
R/S Rhizosphere population
Non-rhizosphere population

11.14 4.35 5.49 4.20 2.11








June 1979

Philippine Phytopathology

0 Initial population before planting

9 Non-rhio.phere soil
2 Rbhizophere soil

099 099 099 099 09 0 9 099 0 099

Plant Echinochloa Eleusine
species colonum indica

Portulaa Amaranthus
oleracea !inoulI

Zea Phaseolus Orya
may aureus sativ

Fig 2. Comparison of Pseudomonas solanacearum initial population in the soil with
the population detected 9 weeks after planting of the various test plants.

The rate of population decline of the
bacterium in bare fallow soil is compar-
able to that in the weed species (Table 3).
It appears, therefore, that keeping the soil
re fallow without cultivation is not ad-
visable if quick reduction of P. solana-
cearum population is desired. Sequiera
(1958) reported that infested soil should
be disked and fallowed for an effective
control of the wilt organism attacking
banana as the organism is highly suscepti-
ble to desiccation. Kincaid (1960) report-
ed that clean fallow for 4 years gave less
wilt control than 4 years of corn. Crosse
(1957) noted that P. solanacearum had
been known to survive for 4 to 6 years in
bare fallow soil. The findings of the
present study, therefore, indicated the
probable reason for these observations.
Decline of the bacterium's population in
soil planted to corn was greater than
fallow soil resulting in less wilt incidence
for corn.

In an effort to determine whether
latent infection of P. solanacearum
occurred in the test plants, stems of these
plants were cut, and placed into sterile
water. When suspensions were streaked
onto Nesmith-Jenkins' or TZC medium,
negative results for P. solanacearum were
obtained, except for some common purs-
lane plants. Colonies with the character-
istics features of P. solanacearum were
recovered from suspensions coming from
some common purslane plants not exhi-
biting any vascular discoloration. This
indicated that latent infection of P. sola-
nacearum occurred in common purslane
which could have probably aided in the
perpetuation of the baterium. Likewise,
Berg (1971) was able to isolate the SFR
strain of P. solanacearum from 12 weed
species growing in banana plantations in
Honduras. Earlier, Dukes et ai. (1965a)
reported that Solanum carolinense L.,
common weed in South Georgia, rarely

Time 099

Vol. 15

Survival of Paeudnmonas Solanacearum

Table 3. Changes in population of Pseudomonas solanacearum in non-rhizosphere soil
after 9 weeks of growth with different plant species

Species planted P. solanacearum Statistical
(X 10' )/g soil Significance

Portulaca oleracea 5.39 a
Eleusine indica 3.56 b
Echinochloa colonum 3.10 bc
Vigna radiata 2.68 bcd
Control (bare fallow) 2.11 bcde
Amaranthus spinosus 2.04 cde
Zea mays 1.26 de
Oryza sativa 0.82 e

a Mean of three replicates; obtained from surface plating 0.2 ml aliquots of 10 10
and 10's dilutions of soil on Nesmith-Jenkins' medium with three replications per
Any two means having a common letter are not significantly different at 5% level with
Ducan's Multiple Range Test.

showed symptoms of wilting although
infection occurred.

Table 5 summaries the results obtained
from the bioassay for bacterial wilt using
susceptible 'Yellow Plum' tomato plants
as indicator plants. The results were
in concurrence with those obtained
in the population study. Soils previously
planted to P. oleracea had the highest
percentage of wilting. Previous planting
of the other three weed species resulted
in wilting percentages not significantly
different from those resulting from pre-
viously fallow soil and soil previously
planted to P. oleracea.

Corn and rice, in turn, caused signifi-
cant reductions in wilting incidence com-
pared to bare fallow soil and weed species
after 9 weeks of growth. It can be expect-
ed, therefore, that successive planting of
either corn or rice in P. solanacearum-in-
fested soil would result in reduction of
the bacterium population in the soil.

Results of the study suggest a positive
role of weed species in the survival of P.
solanacearum in tomato-growing areas in
the Philippines. The weed species name-
ly, E. colonum, E. indica, P. oleracea and
A. spinosus had caused slow but gradual
decline of the bacterial population in
infested soil, while the two crop species
(corn and rice) resulted in faster reduc-
tion of population levels. The rhizo-
spheres of the weed plants presumably
provided a favorable site for reproduc-
tion and multiplication of the pathogen,
thus, enhancing its survival even though
host crop plants were absent. Plants are
known to release diffusates, nutrients like
amino acids and sugars, which could
be utilized by microorganisms living in its
rhizosphere (Rovira, 1963).

The results with corn and rice suggest-
ed their inability to support P. solana-
cearum in their rhizospheres. The present
study, thus, confirms the field observa-
tion that rice and cor arc reliable rotation

June 1979

115 Philippine Phytopathology Vol. 15

I 7.0276 O.o0S,6

e / .-.......... ./

Y 7.238 0.0877X


: 6

-- oea-rhisoaphere so

Rhisspheer soil


"I 7.21 0.07x

7 7.027 0.0802x *


SS Nno-rhzosphare soil

-..- Rhiseophbre noil

TlHs IR vEsK

akma m 1R

Fig. 3. Population changes of Pseudomonas solanocearum in rhizosphere and non-rhizo
sphere soils of jungle rice, (Echinochloa colonum) and goose grass, (Eleusine

e 1979 Survival of Pseudomonas Solanacearum 116

fe 4. Regression analysis for the change in log, o population of Pseudomonas solana-
cearum in the rhizosphere and non-rhizosphere soils of several plant species in
relation to time

it Species Regression Equation

inochloa colonum
zosphere Y = 7.0276 0.0346x
i-rhizosphere Y = 7.238 0.0877x

isine indica
zosphere Y = 7.21 0.0576x
i-rhizosohere Y = 7.027 -- 0.0802x

S,.-- T 6.857 + 0.060o


o*- aoB-rhtswphere Mifl


"? 7.254 O.o869z

Won-rbhisophere 8

.*** htsophbere oil


onas solanacearum in rhizosphere and n
lane (Portulaca oleracea) and spiny amara

o 3

S- *7.132 0-.0861X

1 6

Fig. 4. Population changes of Pseue
rhizosphere soils of common
(Amaranthus sphnosus)

Survival of Pseudomonas Solanacearum




f 6.958 o.U5z


No-rbisolphTer soil

S hiseopher* soil

0 1 2 3 4 5 6
as ain vEm

mai mM


T 7.o12 0.087

6.699 0,o07,4x


-- I-rhissphere soil

--* Rhisoephere soil

Fig. 5. Population changes of Pseudomonas solanacearum in rhizosphere and non-
rhizosphere soils of corn (Zea mays) and mungbean (phaseolus aureus).



0 1 @ 1 4 i 7 9
2 1I IIN V
2a9 z w1M


June 1979

? 7.226 0.153I

Philippine Phytopathology

Vol. 15

r 6.98 O.0859x *

. 7.






I 7.128 o.18zx

Non-rhios . re o'

--- RShizosphre A~c .:

= 6.878 0.162x

Fig. 6. Population changes of Pseudomonas solanacearum in bare fallow soil and in rhizo-
sphere and non-rhizosphere soils of rice (Oryza sativa).

S 1 24 87 S

0 1 2 3 4 S 6 7 '
Tr IN VI vWu

Survival of Pseudomonas Solanacearum

Table S. Comparison of the percentage wilting of susceptible 'Yellow Plum' seedlings in
Pseudomonas solanacearum-infested soil in which various plant species had been
planted previously for 9 weeks.

Plant Species Wilted (Dead) Difference from
Plantsa controlb

Control (bare fallow) 61.19 -
Eleusine indica 62.88 1.69 ns
Portulaca oleracea 70.87 9.68 ns
Echinochloa colonum 53.33 7.66 ns
Vigna radiata 44.14 17.05 *
Amaranthus spinosus 40.31 20.88 *
Oryza sativa 34.05 27.14**
Zea mays 28.49 32.70**

a Average of three replicates with 39 to 60 plants per replicate

b LSD0.05 = 16.33; LSDO.01 = 25.23
significant at 5% level
** significant at 5% level
ns not significant

serve as indigenous reservoirs of inoculum
in virgin soils, or as primary sources of
inoculum in field soils in between plant-
ing of susceptible crops. Control of these
weeds could possibly lower bacterial wilt

incidence in tomato areas in the Philip-
pines, while the rotation of crops with
rice or corn would aid considerably in the
reduction of the disease.


BERG, L.A. 1971. Weed hosts of the SFR strain of Pseudomonas solanacearum, causal
organism of bacterial wilt in bananas. Phytopathology 61: 1314-1315.

CROSSE, J.E. 1957. The dispersal of bacterial plant pathogens. pp. 7-12. In C. Horton-
Smith (ed.). Biological aspects of the transmission of disease. Oliver and Boyd
Ltd. Edinburg.

CHAN, H.H. and A.J. QUIMIO. 1978. Comparison of media for detecting Pseudomonas
solanacearum E.F. Smith in some Philippine soils. (Abstr.) Philipp. Phytopathol.
14: 8-9.

DUKES, P.D., S.F. JENKINS, C.A. JAWORSKI, and D.J. MORTON, 1965a. The iden-
tification and persistence of an indigenous race of Pseudomonas solanacearum in
soil in Georgia. Plant Dis. Reptr. 49: 586-690.

June 1979

PhilinninA Phvtnnathnlonv

by Pseudomonas solanacearum in Soi

JOHNSON, L.F. and E.A. CURL. 1972.
borne plant pathogens. Burgess Publ.

KATZNELSON, H. 1963. Nature and imp
W.C. Snyder (eds.) Ecology of soil-b<

NS. 1965b. Infection of indigenous hosts
leorgia. Phytopathology 55: 1055

hods for research on the ecology of soil-
Minnessota. 247 p.

nce of the rhizosphere. In KF. Baker and
plant pathogens. Univ. of California Press,

Vnl 1.5

..l- I 0

gnus af WF55 rumissupuu. Klea&uma Lmmu5
to nudntain variation in P. oryzae.

Y paClr tou WaUIIIeausn ae& i u tLW ut neve
appears to provide a genetic mechani

"* var *7 1

r ..uzpy..w nl~ry b~yats~avs

MATERIALS AND METHODS ed between me complementary auxo-
trophs. Among the 24 combinations
The isolate of P. oryzae (wild-type) tested, microculturing of two markers
employed in the present investigation was with different nutritional requirements
a single spore culture of race P 150 viru- (greyish-2 x pink-1 met-3) yielded one
lent on rice in repeated trials. Media heterokaryon on minimal medium and
routinely employed and the isolation and the growth was not comparable and
characterization of auxotrophs were done slightly less than the wild type. The hete-
as described earlier (Manibhushan Rao rokaryotic colony was greyish and brown
and Suryanarayanan, 1971). when compared to the greyish histidine
Mutagenesis with NTG (N-methyl-N'- and pink methionine parental isolates.
nitro-N-nitroso-guanidine) was found to Further, heterokaryon formation was not
be more efficient than UV irradiation, a case of reversion or cross feeding since
Aqueous conidial suspensions were pre- both parental types were recovered from
pared from 6-8 day old cultures to which conidia produced on colonies grown from
NTG was added to obtain a final concen- a single hypha when random sampling
tration of 0.1 mg/1. The mixture was was done.
agitated for one hr and NTG and the
nutrients removed by washing the coni- Segregation and recombination studies
dia three times using centrifugation and
resuspension in sterile water. Random sampling of conidia from the
For synthesis of heterokaryons, a heterokaryon showed that from 156
number of techniques viz., hanging drop conidia, two were prototrophic on mini-
technique, streaking method, UV in- mal medium (MM) and these were sub-
duction and growth on mating medium cultured to MM agar slants (Table 2).
(twice concentrated complete medium When single conidia of these prototrophs
(CM) was absorbed with 10% activated were cultured on supplemented MM they
charcoal) were used. showed segregation or recombination of
the characters of the parents. Two coni-
RESULTS AND DISCUSSION dia could grow on MM showing the dip-
loid characters. Conidial length varied
Isolation of mutants considerably. Conidial volume of pre-
sumptive diploids of P. oryzae was re-
Specific biochemical mutants of P. ported to be significantly larger than that
oryzae were successfully screened and the of wild type conidia (Genovesi and
highest frequency of mutants was obtain- Magill, 1976).
ed when NTG was used at concentration That the prototrophs were probably
of 0.1 mg/ml. However, with pink-1, a diploid may be inferred from the fact
colour mutant, the percentage of auxo- that they subsequently produced auxo-
trophs among survivors was.slightly lower trophic segregants which presumably re-
(Table 1). Twenty two mutants were suited from mitotic recombination and
isolated, of which 19 were identified as haploidization. Table 3 shows the segre-
auxotrophs and 3 as colour mutants. gants obtained among single spore isolates
from two putative diploids of P. oryzae.
Formation of heterokaryons in culture Pontecorvo et al. (1953) distinguished
between diploids and haploids in Asper-
Heterokaryons were not readily form- gillus nidulans on the basis of prototro-

- --- --

Genetic Recombination in Pyricularia

Table 1. Auxotrophic and colored mutants obtained after mutagenic treatment of Pyri-
cularia oryzae Cav.

Cone. of NTG Colonies Auxotrophs Auxotrophs Colored Colored
used examined isolated among mutants mutants
(n'g/ml) (No.) (No.) survivors isolated survivors
(%) (No.) (%)
50 377 4 1.06 1 0.27
100 380 11 2.89 2 0.53
200 300 1 0.33 0 0.0
100a/ 320 3 0.94 0 0.0

a/Pink colored mutant, pink-1.

phic growth, conidial size, recombination
and through the sexual cycle. No perfect
state is reported in P. oryzae although it
was reported in P. oryzae on crab grass
(Herbert, 1971). However, Kato et al.
(1976) produced perfect state by mating
P. oryzae with P. grisea f. sp. eleusinae
from ragi but not within P. oryzae. Fur-
thermore, with no easily applicable

criterion of chromosome number and
conidial length, the interpretation of the
results is difficult. However, our obser-
vations seem to show that in P. oryzae
heterokaryosis plays a part in genetic
recombination outside the sexual stage
although the frequency of heterokaryon
formation reported here was consider-
ably lower than that found in other fungi.


H. KOIDE. 1975. Occurrence of rice blast and causal races on breeding lines with
resistance gene Pi-zt derived from Toride No. 1. Kanto-Tosan P1. Prot. Soc. Proc.
22: 14-15.

GIATGONG, P. and R. A. FREDERIKSEN. 1969. Pathogenic variability and cytology
of monoconidial subcultures of Pyricularia oryzae. Phytopathology 59: 1152-1157.

GENOVESI, A. D. and C. W. MAGILL. 1976. Heterokaryosis and parasexuality in Pyri-
cularia oryzae Cavara. Can. J. Microbiol. 22: 531-536.

HEBERT, T. T. 1971. The perfect stage ofPyricularia grisea. Phytopathology 61: 83-87.

International Rice Research Institute. 1975 Annual Report for 1976. Los Banos, Laguna,
Philippines, p. 207.

KATO, H., Y. YAMAGUCHI, and N. NISHIHARA. 1976. The perfect state of Pyricu-
laria oryzae Cav. in culture. Ann. Phytopathol. Soc. Japan 42: 507-510.

KIYOSAWA, S. 1974. Studies on genetic and breeding of blast resistance in rice. Miscl.
Publ. Nat. Inst. Agr. Sci. Ser. D. 1: 58.

June 1979

T7.Al 7

Biochemical markers and its colony color
observed at randomly harvested conidia
No. of CM MM grey pink gray
markers h-2 his-2 met-8

1 25 25 0 9 4 5
26- 50 23+ 0 17 4 0
51- 75 25 1 14 4 8
76- 100 24+ 0 14 5 0
101- 125 25 0 16 2 2
126- 150 22+ 1 10 2 4
151- 156 6 0 5 1 0
Total 150 2

*Average of 4 replicates

Table 3. Recombinants recovered from two putative diploids of P. oryzae

Biochemical markers and its colony color
at randomly harvested conidia

Serial No. No. of
ofthe spores CM MM grey pink grey
diploid tested* hs-2 his-2 met-2

58 35 35 6 14 6 3
141 26 25+ 3 16 3 1

*Average of 4 replicates

OU, S. H. and M. R. AYAD. 1968. Pathogenic races of Piricularia oryzae originating froi
single lesions and monoconidial cultures. Phytopathology 58: 179-182.

OU, S. H., F. L. NUQUE and J. M. BANDONG. 1975. Relation between qualitative an
quantitative resistance to rice blast. Phytopathology 65: 1315-1316.

BUFTON. 1953. The genetics of Aspergillus nidulans. Adv. Gent. 141-238.

SUZUKI, H. 1967. Studies on biologic specialization in Pyricularia oryzae Cav. Toky
Univ. Agric. Technol., Tokyo, Japan 235 p.

WU, H. K. and T. M. TSAI. 1975. Studies on variation in pathogenicity of Pyric
laria oryzae Cav. 1. Mechanism of genetical variation. Memoires of College <
Agric. Nat. Taiwan Univ. 15: 7-21.

YAMASAKI, Y. and H. NIIZEKI. 1965. Studies on variation of rice blast fungus Pil
cularia oryzae Cav. 1. Karyological and genetical studies on variation. Nat. Ins
Agric. Sci. Bull. Ser. D. 13: 231-274.

Philipp. Phytopathol. 15(2): 127-136
Received for publication: 20 August, 1979



Former graduate student, now instructor at Mariano Marcos Memorial State Univer-
sity and assistant professor respectively, University of the Philippines at Los Banos, Col-
lege, Laguna.

Portion of the master's thesis of the senior author.


Four species of Pythium were isolated and identified from a total of
510 soil samples collected from 51 tobacco-growing municipalities of the
Ilocos Region. These were P. debaryanum, P. aphanidermatum, P. monosper-
num and P. ultimum listed according to their relative frequency of occurrence.
The last three species were the first report of the genus infecting tobacco in
the Philippines.

The virulence of the four species were compared using eight varieties
of tobacco, namely: Yarda, Giant Cocker, NCBY, 100 leaves, Turkish, Zota,
Simmaba and Reax. P. debaryanum was the most virulent as the cause of
pre- and post-emergence damping-off. It also significantly reduced seedling
height. Among the tobacco varieties, Yarda was most resistant to the attack
of the organism; NCBY, 100 leaves, Simmaba and Reax were susceptible,
Turkish slightly susceptible, and Zota very susceptible.

Tobacco (Nicotiana tabacum L.) had disease of tobacco. It is so pathogenic
become the most important cash crop in that once infection started in a small area
the provinces of Ilocos Norte, Ilocus Sur, of the seedbed, the whole seedbed will
Abra, La Union, and Pangasinan since be wiped out unnoticed within 3 to 7
1953, when the flue-cured Virginia tobac- days.
co was introduced. However, just like in Except for the report of their occur-
the Cagayan Vall-y, the cigar type had rence, studies on Pythium spp. in the
also been grown in these provinces since I
Ilocos Region are lacking. It is there-
the Spanish regime. fore, an objective of this investigation

Like any other field crops, the tobacco to make a study of the distribution of the
however suffers from devastating mala- different species in the area. As there is
dies resulting to great loss to its grower. no damping-off-resistant variety of tobac-
The culture of tobacco seedlings makes co found so far, screening of tobacco
the crop susceptible to soil-borne patho- varieties for resistance to damping-off
gens, one of which is Pythium. would be of value in selecting resistant
plants to reduce the ravages of the dis-
Seedling damping-off caused by various ease. Therefore, pathogenicity tests on
species of Pythium is a common seedbed different varieties of tobacco were also

June 1979 Survey of Pythium 128

undertaken to check their resistance to- growth, several of which have sporangia
particular species of Pythium. with swarming zoospores, were carefully
separated and planted on the center of
MATERIALS AND METHODS water agar plates. These were incubated
at room temperature.
Collection of Soil Samples
Growth of the organisms on plated

Soil collections were made from water agar was observed daily until the
December 1976 to March 1977, a period appearance of vegetative as well as re-
which coincided with the season when productive structures. Their mode of
growth was noted, their vegetative and
tobacco seedlings were grown on seed-

10 cm deep around the root zone ot the
seedlings. Soil samples about one half
liter each, were placed in plastic bags The monograph of Midd
The monograph of Middli
and tied with rubber bands. Ten sam-
was used in the identification
ples from different sites were taken from However, other literature
each town. Soil collection was made three
(1949, 1960) and Feel i
times: one during 3rd week of January (1949, 16 and Fel
(1975)) were also consulted.
and the last on the last week of March.
After each trip, collected soil samples
were stored in the Mycology Laboratory Pu utres o te
of U.P. at Los Banos, where isolation of Pythium were deposited a
and identification were done. Culture Collecton (FCUP) o
ment of Plant Pathology, I
Isolation and Identification of Pythium Bafios.

Sorghum seeds were used in the iso- Pathogenicity and Virulence 1
lation of Pythium spp. from the soil
samples. Seeds were boiled in water for 5 Pathogenicity tests on to
minutes cooled and then cut into lings were done in the gre
halves with a scalpel. Prior to baiting, the Department of Plant
aliquots of soil samples were dispensed from October 29 to Decemlx
in sterile petri plates and were flooded Four species of Pythium,
with distilled water. Three of four seeds aphanidermatum, P. debam
were placed in each pl-te and were in- monospermum and P. ultimur
cubated for 3 to 4 days. isolated from the previous
were used to inoculate eig
Colonized baits were washed first of tobacco grown in the Ilo
in tap water and rinsed several times in The varieties were Yarda, Gi
sterile water. Cleaned colonies were trans- NCBY, 100 leaves and Turki
ferred to other sterile petri plates with type), Zota (Burley), Simmat
small amount of distilled water. and Reax (Filler).

With the aid of a dissecting micros- The inocula were grown

in (194
if special
i Masi

id spec
ie Funl
ie Depa
'. at L


cco see
27, 197
all newly
s Regic
t Cocki


and the soil-fungus mixtures characteristics of the species:
ed for 8 days to give the or- permum: sporangium filament
to establish themselves and ly inflated; oospore plerotic
thin the sterile soil. Planting dium monoclinous, or diclinoi
watered everyday including dial cell typically terminal: :
ots. They were covered with flated, clavate and crookneck
heet up to the time the IA). P. aphanidermatum: spo
ready for sowing the seeds. mentous, very much inflated
aplerotic antheridium diclinoi
ays, infested soil was placed dial cell terminal, barrel or doi
ri plates and were planted sub-orbicular or broadly cli
seeds. There were five treat- during conspicuous penetra
ch treatment had four repli- (Plate I, B). P. ultimum: s
globose; antheridium usually 1
nous, originating immediately

cal counting for post-emergence globose; antheridium ranges from 1-5
ring-off was made 45 days after per cogonium and diclinous, not origi-
ng. nating immediately adjacent to the oogo-
arietal resistance was noted using an
L based on the number of surviving Table 1 shows the frequency distribu-
ings 15 days and 45 days after tion of the four species of Pythium in the
ig. The index used was: 1 highly five major provinces of the Ilocos region.
ant (95-100 seedlings), 2 resistant In all the provinces, P. debaryanum
4 seedlings); 3 moderately re- predominated in the soil isolations, fol-
it (75-84 seedlings); 4 slightly lowed by P. aphanidermatum, except
ptible (55-74 seedlings); 5 suscep- in La Union where, no isolation of this
(55-64 seedlings); and 6 very sus- latter species was made from out of 100
ble (54 and below), soil samples. P. ultimum ranked next,
except in Pangasinan where no isolation
...... -.............. of this species was made. P. monosmer-

Survey of Py thium





June 1979

Philippine Phytopathology


A. P. monospermum Pringsheim Jabrb. A and B, typical filamentous sporangia; C.
intercalary sporangium; D, acrogenous oogonium with monoclinous antheri-
dium and plerotic oospore; E, acrogenous oogonium with monoclinous and
diclinous antheridia; F, acrogenous oogonium with diclinous antheridium.

B. P. aphanidermatum (Edson) Fitzpatrick. A, B and C, inflated filamentous spo-
rangia; D, sporangium with vesicle containing zoospores, outside vesicle are
mature reniform zoospores; E, encysted zoospore producing germ tube; F,
oogonium with aplerotic oospore and diclinous antheridium.

C. P. ultimum Trow. A, terminal globose sporangium; B and C, typical oogonia with
aplerotic oospore and monoclinous antheridium; D, oogonium with both
monoclinous and diclinous antheridium; E, intercalary sporangium.

D. P. debaryanum Hesse. A and C, intercalary sporangia; B, terminal globose spora-
ngium; D, sporangium with vesicle containing zoospores; E, terminal oogo-
nium with 1 monoclinous antheridium and 2 diclinous antheridia; H, oogo-
nium with 5 diclinous antheridia.

tobacco, followed by P. ultimum, P.
aphanidermatum and P. monospermum
respectively. It should be noted that P.
debaryanum also gave the highest relative
frequency in soil isolations from all the
provinces, while P. monospermum which
seemed to be the least virulent, gave the
lowest frequency.

P. debaryanum as an important cause
of pre-emergence damping-off had been
reported by Pakdi and Claridad (1971).
On their screening test of 51 varieties of
tobacco against P. debaryanum, 8 varie-
ties were considered highly resistant; 10
resistant and 14 susceptible. This is fur-
ther evidenced by the report of Bogo-
yavlenska (1975) that P. debaryanum
had caused the destruction of tobacco
seedlings in Maldavia.

The pathogenicity of P. debaryanum
was already reported by Clara (1925)
in the Philippines.

Among the eight varieties tested in this
study, Yarda seemed to be moderately
resistant, while Giant Cocker, 100 leaves,
Turkish and Reax were susceptible. From
the report of Pakdi and Claridad (1971),
Turkish, Simmaba and Burley were sus-
ceptible to pre-emergence damping-off
caused by P. debaryanum.

P. ultimum was considered second in
pathogenicity to tobacco seedlings. An
earlier report was made by Wilhelm
(1915) who stated that P. ultimum is
primarily the cause of pre-emergence
damping-off of tobacco and is respon-
sible for poor plant growth.

In this present study, Yarda was found
to be resistant to P. ultimum; while Tur-
kish was slightly susceptible; Giant Cock-
er, NCBY, 100 leaves, Simmaba and
Reax were susceptible; and Zota (Bur-
ley) was very susceptible. These findings
corroborate with the report of Orellana

Vol. 15

locos Nortea Ilocos Sur
Relative Relative
Frequency Frequency Frequency Frequency Frequency
% % %

um 52 53 52 66 51
n 23 28 13 16 10
7 8 9 11 8
rmum 0 0 4 5 1
aOut of 130 soil samples dOut
Out of 60 soil samples Out

average number of germinated seedlings 15 days after sowing in pre

riety Inoculated with Inoculated with
P. aphanidermatum P. debaryanum

nt Cocker 79 60
rda 85 75
" BY 62 40
3 leaves 85 55
rkish 64 55
ta 35 30
imaba 47 41
ax 69 45

ut of 100 seedlings. Control plates gave 100% germination.

Table 3. Varietal resistance to pre-emergence damping-off caused by Pythium spi

Pythium Pythium Pythium Pythiu
Variety aphanidermatum debaryanum monospermum ultima

Giant Cocker 3 5 2 5
Yarda 2 3 1 2
NCBY 5 6 4 5
100 leaves 2 5 2 5
Turkish 4 5 2 4
Zota 6 6 6 6
Simmaba 5 6 5 5
Reax 4 5 5 5

aSymbols used:
1 Highly resistant (95-100 seedlings up to 15 days)
2 Resistant (85-94 seedlings up to 15 days)
3 Moderately resistant (75-84 seedlings up to 15 days)
4 Slightly susceptible (65-74 seedlings up to 15 days)
5 Susceptible (56-64 seedlings up to 15 days)
6 Very susceptible (54 and below seedlings up to 15 days)

(1953) that in Venezuela, P. ultimum pathogenic to tobacco, although it is t
causes severe pre-emergence damping- least virulent among the four spec
off losses on seedbeds planted to Vir- compared. Yarda was highly resistal
ginia and Burley tobacco. Giant Cocker, 100 leaves and Turki
were resistant; NCBY was slightly susce
P. aphanidermatum ranked third in tible, Simmaba and Reax were suscep
virulence. Yarda and 100 leaves were ble; and Zota (Burley) was very susce
resistant; Giant Cocker was moderately tible.
resistant; Turkish and Reax were slightly Middleton (1943) earlier reported
susceptible; NCBY and Simmaba were monospermum as causing tobacco danm
susceptible; and Zota (Burley) was very ing-off. However since P. monospermu
susceptible. This confirms earlier reports was rarely isolated in the Ilocos Regii
made by Teakle (1960), and Mathrani it can be considered as minor in econonr
(1960). importance as a tobacco damping-(
causal organism.
P. aphanidermatum as a causal organ-
ism of damping-off of tobacco has been Post-emergence damping-off Table
reported in Queensland, India, France, shows the average number of seedlin
South Africa, Gold Coast, Carolina and that survived 45 and 60 days after so,
Indonesia (Pakdi and Claridad, 1971). ing while Table 5 shows the rosultij
There is no doubt that in the Philippines, varietal resistance to post-emergen
this species could thrive and parasitize damping-off caused by the four specie
seedlings of a number of tobacco varie-
ties. A similar trend in pre-emergen
damping-off is noted in post-emergen
P. monospermum was also found damping-off with P. debaryanum as tl

Table 4. Average number of surviving seedlings 45 and 60 days after sowing in pre-infested soil

Average number of surviving seedlingsa
Type Variety Inoculated with Inoculated with Inoculated with Inoculated with
P. aphanidermatum P. debaryanum P. monospermum P. ultimum

45 days 60 days 45 60 45 60 45 60
Virginia Giant Cocker 74 71 49 38 94 94 91 90
-do- Yarda 57 55 41 38 76 76 61 61
--do NCBY 82 82 51 44 89 89 54 54
-do -- 100 leaves 82 82 51 44 89 89 54 54
-do Turkish 76 73 52 44 91 89 67 64
Burley Zota 38 38 30 28 37 37 31 31
Wrapper Simmaba 53 53 41 38 47 47 55 54
Filler Reax 61 61 54 50 59 56 44 43

aOut of 100 seedlings. Control plates gave 100%? germination.

'able 5. Varietal resistance to post-emergence damping-off caused by Pythium spl

Pythium Pythium Pythium Pythiu

N U BY 0
100 leaves 3
Turkish 3
Zota 6
Simmaba 5
Reax 5

aSymbols used:
1 -- Highly resistant (95-100 seedlings
2 Resistant (85-94 seedlings 45 up ta
3 Moderately resistant (75-84 seedlii
4 Slightly susceptible (65-74 seedlin
5 Susceptible (55-64 seedlings 45 up
6 - Very susceptible (54 and below)

most pathogenic, followed by P. ulti
mum then P. aphanidermatum and P
monospermum as the least pathogenic

The apparent increase on the number:
of seedlings 45 days after sowing may be
due to the fact that after the counting or
pre-emergence damping-off, some seed:
still germinated which increased the num
ber of seedlings up to the time the 45
day-period was reached. However, it
some plates, there was a rather decrease
in the number of seedlings which indicate
ed that there was a positive interactior


of tobacco seedling rot. Tobacco Ab

CLARA, F. 1925. Diseases of tobacco i
171. Phil. Agr. Rev. 18: 564-570.

DRECHSLER, C. 1940. Three species o
ogy. 30: 189-213.

DRECHSLER, C. 1960. Pythium causing
Sydowia 14 (1/6): 4-20.

6 3 5
5 2 4
5 2 4
6 6 6
6 5 5
5 5 6

up to 60 days)
) days)
45 up to 60 days)
65 up to 60 days)
60 days)

between the host and the pathogen.

It was found that among 45-day-ol
seedlings, Giant Cocker was susceptible
to P. debaryanum, and all the other sever
varieties were very susceptible; the same
case occurred when they were 60 days
old. A more or less similar result had beer
reported by Pakdi and Claridad (1971,
who stated that tobacco varieties were
affected in varying degrees of severity
by damping-off disease due to P. debarya


S1975. Pythium perniciosum, a causal ageni
19: 6.

ie Philippine DANR. Bureau of Agric. Circ

Othium associated to root rots Phytopathol

n rot of tobacco in Nicaragua and Indonesia

vey or ryrmum

nov) can. J. of Bot. 53 (24). 2908-2922.

FHRANI, D. 1960. Diseases in Flue-cured

IDLETON, J. 1943. The taxonomy, host
genus Pythium. Mem. Torrey Bot. Club. S

ELLANA, R 1953. Copper sulphate for th
bed. Phytopathology 43: 125-127.

IDI, S. and F. CLARIDAD. 1971. Screen
to damping-off disease caused by P. de

LKLE, D. 1960. Species of Pythium in Quef

,HELM, S. 1965. P. ultimum and the soil
ogy 55: 1016

bacco. Indian Tobacco 10 (3): 171-7.

ge and geographic distribution of the

)ntrol of damping-off in tobacco seed-

.f some tobacco varieties for resistance
'anum Hesse. Araneta J. Agr. 18 (3):

nd J. Agr. Sci. 17 (1): 15-31.

igation growth response. Phytopathol-


Received for publication: 8 September,



1Virologist, Graduate Student, an
trol Laboratory, Institute of Plant Bree
College, Laguna, Philippines

The authors are grateful to Dr.
Pathology, UPLB, College, Laguna, for al


The counterimmunoelectn
TMV-0 antigen in orchids. It wa
sensitive and specific serological p
cations in mass indexing of orchi
rantine work.

The occurrence and identity of toba
co mosaic (TMV-O) and cymbidiu
mosaic (CyMV) viruses in imported c
chids became known only recently (Rill
1978). As a consequence, efforts are ct
rently underway to minimize the fourth
introduction of orchids in small or coi
mercial quantities unless they pass
appropriate quarantine testing proc
dures. Information is also lacking regard
ing the relative incidence and distribution
of these viruses in established nurseri
in the Philippines.

Detection of orchid viruses is a dif
fult and oftentimes a complicated tas
It involves careful visual examination
orchids for symptoms of virus infecti4
and, when symptoms are inapparent, le
tissue samples are indexed by mechanic
transmission studies onto a set of vir
indicators or differential hosts. Oth
tests particularly those based on serol




Research Associate, respectively, Virus Bioco
g, University of the Philippines at Los Banc

G. Divinagracia of the Department of Pla
ring the use of his orchid plants.


oretic technique was used to detect
found to be a simple, rapid, eomemical,
edure. The technique has potential appli
n established nurseries and in plat qua-

gical reaction between antigen and i
specific antiserum are utilized.
We describe here a laboratory proc
dure that could be used to index orchi!
for TMV-O. The technique is rapid ar
specific. It will detect TMV-O antigen i
leaf extracts in nanogram quantities.


The orchid strain of tobacco mosa
virus was obtained from an infected
Laeliocattleya 'Randy'. It was kind
provided for our use by Dr. G.G. Divin
gracia of the Department of Plant Pathc
ogy, University of the Philippines at LA
Bafios. The virus isolate obtained aft,
repeated single local lesion transfers
Gomphrena globosa was propagated i
the same host plant. Its identification ;
TMV-O was based on particle morph
logy and serological property (Talens, u,
Published observation).

cj -- %-,/ --Uar--,Aaa uiu LWU
es of differential high speed (90 min 1
30,000 rpm in a Spinco FA-type 1
r). Purified virus was resuspended in
5 M phosphate buffer, pH 7.5.

Lntiserum was produced in rabbits by
weekly intravenous immunization of
mg per ml virus protein per injection. 1
;ific antiserum was obtained 7-10
after the last intravenous injection.
end-point titer (1:1024) was deter-
ed using microprecipitin titration (van
teren, 1955).

ounterimmunoelectrophoresis (CIEP)
used to determine the sensitivity and
ificity of the serological technique.
r (1.0% dissolved in 0.025 M phos- 1
e buffer, pH 7.5 and 0.85% NaCI) '
1-2 mm in thickness was prepared
i 25 x 76 mm glass slide. A Grafar (
iple gel puncher was used to bore the

s. Wells were sealed with a small
unt of dissolved agar. One hundred
50 ul of antigen and antiserum pre-
tions were placed on appropriate
s. Electrophoresis was run at 10 mA ,
slide for 15-30 min using 0.025 M
iphate buffer, pH 7.5. Slides were
rined for the precipitin lines using a
-field illuminator. To enhance con-
, slides were stained for 2 hr with
% Coomassie blue and destined in
!r for 12-24 hr at room temperature


litial CIEP run indicated that TMV-O r
ific antiserum when used at a dilution a
:64 to 1:128 yielded sharp precipitin p
at antigen concentrations ranging v
i 5-100 ug per ml (Fig. la). Further- V
e, when CIEP agar gel was stained in
% Coomassie blue a thin band was

cn was not previously visualized in
trained preparation. Thus, for routine
)ratory testing, results of CIEP were
rded after each run and again after
iing with 0.025% Coomassie blue.

o establish the specific reaction be-
en TMV-O antiserum and its homo-
>us antigen, CIEP was conducted
zing several homologous and hete-
gous antigen sources including Laelio-
leya 'Randy' from which TMV-O was
finally isolated (Rillo, 1978). Purified
IV was included as a negative antigen
trol. It is apparent from Fig. 2 that
V-O antiserum only reacted with
gen preparations from tobacco infect-
with a common strain of TMV and
iocattleya 'Rapdy' infected with
1-0. No other precipitin lines were
irved even after staining with 0.25%
massie blue.

several orchid plants which were
wn to be infected singly or doubly
I TMV-0 and CyMV (Chansilpa, un-
lished observations) were used as
ce of virus antigen. Only Aranda
istine' No. 1 and Catlleya 'Queen
:it' were symptomless; Aerides, Cym-
Um, Laeliocattleya 'Randy' and
idium showed symptoms of virus
:tions. Fig. 3 shows that both Chris-
No. 1, Queen Sirikit and Randy
id plants showed positive precipitin
tions. Except for Oncidium in which
thanical transmission studies suggested
presence of TMV-O (Rillo and Chan-
, unpublished observations), the
Its of CIEP were in good agreement
the bioassay. Further tests are being
ned to determine the identity of the
agent in Oncidium orchid plant
:h incited reactions in virus indica-


_ ________ __ _____

uippme rnyuopau

Fig. 1. Detection limits of TMV-O by c
stained (b) agar gel. Numbered
in microgram. Wells labeled As
1:64. Photographs were taken
(a) and after staining with 0.259

Fig. 2. Specificity test of TMV-O spe
analysis in agar gel. Numbered
infected orchid, (2) uninfected
TMV-O, (4) infected Cymbidiu
TMV, and (6) purified CyMV.
rum diluted at 1:64. Photogr

Fig. 3. Counterimmunoelectrophoretic
bered wells contained leaf sal
(3) Oncidium 'Golden Shower
and (6) Aranda '.Christine' No
antiserum diluted at 1:64. Phot

iterimmunoelectrophoresis in unstained (a) ai
Is contained indicated amount of virus prote
stained TMV-O specific antiserum diluted
aediately after counterimmunoelectrophore
omassie blue (b).


: antiserum by counterimmunoelectrophon
Is contained antigen preparations from (1)
iacco, (3) Laeliocattleya 'Randy' infected w
(5) tobacco infected with a common strain
Is labeled As contained specific TMV-O ant
was taken immediately after electrophore

section of TMV-O in infected orchids. Nu
om (1) Aerides, (2) Laeliocattleya 'Rand
1) Cymbidium, (5) Cattleya 'Queen Siriki
Wells labeled As contained TMV-O speci
iph was taken staining with 0.25% Coomas


pid Detection of TMV

Fhe results of this investigation pro-
: evidence for the use of CIEP as a
sitive, rapid, economical, and reliable
cedure for testing the occurrence of
V-O in orchids. Under optimum con-
ons, the test capable of detecting
logram quantities of TMV-O proteins
ild be accomplished by a trained tech-


,LO, E. P. 1978, Isolation and identificat
on Laeliocattleya 'Randy' and chlorotic
in the Philippines. M.S. Thesis, Unpublish

NSLOGTEREN, D. H. M. 1955. Serologica
oil. Proc. 2nd Conf. Potato Virus Diseasei

is and in 12-24 hours in stained pre-
ations. It eliminates several laborious
I tremendous space requirements in
conduct of mass bioassay for TMV-O.
empts are being made to develop a
,e scale indexing procedure and to
ipare the sensitivity of CIEP with that
bioassay and other serodiagnostic pro-


of the viruses causing mosaic disease
streak on Oncidium "Golden Shower"

icro-reactions with plant viruses under
ssee. Wageningen. 51-54.


j..uipS r. jr .yuu. j ..o J'y.--.
Received for publication: 28 September



Associate Professor, Department c
sity of the Philippines at Los Banos, Coll

This study was supported by UPI
E. Gallardo and Mr. V. Siman in condu


Seven nematicides tested agi
siderably reduced nematode infec
yield. Vydate-treated plants gave
lowed by Hoe 2960-5G, Furadan
plants, taken after the completion
any relationship with the yield. '
phytotoxicity of the chemicals or
occurred after the yield potential
planted as intercrop, showed som
obtained was even lower than th
tive effect on the soil nutrients a

Annually, about 16,700 hectares
land are planted to tomato through
the country with yields that vary frc
2.3 to 10.6 metric tons per hecta
(NFAC, 1976). Pests and diseases are fi
tors that contribute largely to such wi
yield variation. Among these pests a
the root-knot nematodes, Meloidogy,
spp., which in severe cases could cau
more than 50% reduction in yield
tomato (Ducusin & Davide, 1972). 1
cidentally, all the tomato varieties grov
in this country as tested by the auth
are susceptible to root-knot nemato
infection. For the last few years, the
have been some studies done to fii
effective control against root-knot neir
uintcrl Muelh and Dnvitlde 1976 : Ducus




plant Pathology, College of Agriculture, Univ,
, Laguna.

A-NFAC research grant. The assistance of N1
ig the experiment is gratefully acknowledge


t Meloidogyne incognita on tomato con-
i and resulted in a significant increase in
e highest percentage yield increase fol-
and Temik 10G. The gall index of the
Sthe experiment, did not generally bear
was probably due either to subchronic
later reinfection by the nematode which
the plants was realized. Tagetes erecta,
egree of nematode control but the yield
control. This may be due to its competi-
other ecological factors for the tomato

& Davide, 1972). It has been demonstr;
ed abroad that nematicide control
root-knot nematodes on tomato oft
resulted in significant increase in yie
(Kyrou, 1973;Johnson, 1978)

The present study was primarily
signed to evaluate the effectiveness
some locally available nema.icides ai
Tagetes erecta, planted as intercrc
for the control of Meloidogyne
cognita Chitwood attacking toma


The following nematicide, were c'
luated for the nematode con r,!: Ten
10G (2-methl -2 (me thvlthio -:Iopion

rect of Nematicides

S--- ---------r-----,-,J' VI----,
plied by Union Carbide Philippines;
:ap 10G (-O-ethyl S, S-dipropyl
isphorodithioate), supplied by Mobile
ippines; Furadan 3G (-23-dihydro-2,
imethyl-7-benzofuranyl methylcarba-
e), supplied by FMC International;
late (S-methyl l-(dimethylcarbamoyl)
(methylcarbamoyl) oxy]thioformimi-
e), supplied by Du Pont Far East Inc.;
lite (O-phenyl, N, N'-demiethyl-phos-
rodiamidate supplied by Dow Chem-
Pacific Ltd.; Hoe 2960-5G (1-phenyl-
,0-diothyl-thionophosphoryl)-1, 2,4-
zol supplied by Hoechet Phil. Inc.:
Nemagon 20G (1,2-dibromo-3-chlo-
ropane) supplied by-Shell Chemical
(Phil.) Inc. These chemicals were
lied based on the manufactures' re-
imended rates. The experimental
gn used was a randomized block with
The experimental farm, located at the
LB Central Experiment Station, has a
y loam soil. It was thoroughly pre-
ed and subdivided into plots of 1 x 4
:ers. In each plot, two furrows, 30
apart, were dug at 8 cm deep and 10
wide. The nematicides were applied
o these furrows and covered with soil
nediately thereafter. The following
,each furrow was planted with 3-
:k old tomato seedlings VC2-1 pre-
isly grown in small plastic bags and
e inoculated with one eggmass of
incognita per plant before transplant-
Eight tomato seedlings were planted
each furrow at 30 cm apart. In the
etes plot, 1-month old T. erecta seed-
s, previously grown in small plastic
s, were planted 30 cm apart from the
iato plants between the two furrows.
Snon-treated plots were also planted
i tomato seedlings to represent the
trol treatment.

Throughlou; the duration f the expc

ent me plants were suppuea wim aae-
ite fertilizer and periodically sprayed
h insecticide and fungicide to control
:ct pests and fungal diseases. Manual
eding was done regularly to keep the
erimental area free of weeds. Since
experiment was conducted during the
season, artificial watering of the
its through overhead irrigation was
ie once every 2 weeks.
harvesting was done as soon as the
ts were ripe. Data on fruit weights
e taken every harvest and these were
I as basis for the yield evaluation.
it after the last harvest, all the plants
e uprooted and adhering soil particles
e carefully removed from the roots.
gall formation in each root system
indexed and rated as follows; 1 for
galls (0%); 2 for trace (1-25%); 3 for
it ( > 25-50% ); 4 for moderate
50-75%) and 5 for severe galling (over
,). Mean gall index was caicula-
based on the individual gall rating of
he plants in each treatment. The data
the gall index ratings were used as
s for comparing the effectiveness
the different nematicide treatments
the effect of T. erecta as an inter-
Son the control of the root-knot
rhe data presented in Table 1 indicate
t the different nematicide treatments
considerably reduced the root-knot
latode infection on the tomato plants.
ed on the mean gall index ratings,
late treatment gave the highest per-
tage control of the nematode follow-
by Temik 10G, Nellite W.S., Mocap
, Furadan 3G and Hoe 2960-5G.
iato plants in the T erecta treatment
an irdex rating of 3.2 which is conm-
ible to the gall index rating in plants
ted with Hoe 2960-5G ard Nen:gon,


Philippine Phytopathology

Table 1. Root gall index of tomato plants treated with different nematicides and Tage-
tes erecta taken after the last harvest of the crop a

Rate b Replication
Treatment Mean
Per furrow (kg a.i./ha) I II HI IV V

Vydate 40 cc 48.0 1.3 1.0 1.0 1.0 1.0 1.06
Temik 10G 9 g 4.5 2.4 2.0 1.3 1.0 1.0 1.69
Nellite W.S. 30 cc 4.05 2.5 2.3 1.7 1.9 1.9 2.21
Mocap 10G 9 g 4.5 3.2 2.9 2.7 2.7 2.7 2.57
Furadan 3G 30 g 4.5 3.0 2.5 2.6 2.9 2.9 2.91
Nemagon 20G 9 g 9.0 2.5 2.6 3.7 2.9 2.9 3.01
Tagetes erecta 2.9 3.1 3.2 3.6 3.6 3.18
Hoe 2960-5G 24 g 6.0 3.3 3.3 3.1 3.9 3.9 3.20
Control 4.4 3.9 3.9 3.6 3.6 3.82

aThe gall index ratings were as follow: 1 for no galls (0%), 2 for trace (1-25%), 3 for
slight (>25-50%), 4 for moderate (>50-75%), and 5 for severe galling (over 75%).
bNellite and Vydate were botl EC formulations, the required dosage was added 1
U.S. gallon of water per furrow.

Table 2. Yield of tomato plants treated with different nematicides and Tagetes erecta

Replication (Yield Kg)
Treatment Mean a Percentage
I II HI IV V (kg) Increase

Tagetes erecta
Nellite WS
Mocap 10G
Nemagon 20G
Tomik 10G
Furadan 3 G
Hoe 2960-5G





14.65 a
13.80 a
16.29 bc
16.51 be
17.41 b
17.61 b
18.00 b
18.15 b
20.21 brr


aMeans followed by the same letter are not significantly different at P = 0.05 DMRT.

As shown in Table 2, the different
hematicide treatments resulted in signi-
ficant increases in yield of tomato. The
highest yield increase was 37.9% obtained
from the Vydate-treated plants, while
those treated with lHoe 2960-5G, Furadan
3G and Temik 10G gve a yield increase

of 23.9, 22.8, and 20.1%, respectively.
Less than 20.0% yield increase was
observed in plants treated with Mocap
10G, Nemagon 20G, and Nellite W.S.
However, there was no yield increase
obtained in plants intercropped with
'. 'rrcta.

Vol. 15

.liun 1979

effect of Nematicid,

Results maicaie inat ue gaiu mIucx
rating taken at the completion of the
experiment generally bears no relation-
ship with the yield increase in most nema-
ticide treatments. This is particularly true
with Nellite, Mocap and Temik treat-
ments. They seemed to exhibit long last-
ing effect on the nematode but at the
same time probably have some phyto-
toxicity which prevents tomato plants
from giving optimum yield performance
despite the nematode control. Temik 10G
particularly at high dosage may cause
burning of tomato leaves (Chongruksa
and Davide, 1973). The relatively high
galling index in some treatments may be
due to second and possibly third gene-
ration nematode infection upon which
the chemicals may have already less resi-
dual effect on them. The reinfection may
have only occurred after the full yield
potential of the plants was realized;
hence, the treated plants could still show
high yield performance as in the case of
Hoe 1960-5G-treated plants. It has been
shown that root-knot nematode infection
taking place at flowering stage of tomato
plants has much less effect on the yield
than when the infection takes place at
the seedling stage (Ducusin and Davide


ment and sex differentiation of Mel
57: 198-209.

DUCUSIN, A. R. and R. G. DAVIDE. 197
to yield and some methods of control

JOHNSON, A. W. 1978. Effect of nematici
control of root-knot nematodes on t(

KYROU, N. C. 1973. Effect of soil treatma
under field conditions. Plant Dis. Rep

RUELO, J. S. .nd R. G. DAVIDE. 1976.
Meloidogyne incognita on tomato. Ph


On the other hand, the performance
of T. erecta, as an intercrop, though com-
parable with that of Hoe 2060-5G, did
not increase the yield of tomato plants.
It was possible that the effect on the
nematode was overcome by its competi-
tive effect on the soil nutrients, sunlight
and other ecological factors for the toma-
to plants as they were also growing luxu-
riantly and the distance of 30 cm apart
was probably too close to the tomato
plants to withstand such competition.
However, it has been demonstrated that
Tagetes could provide excellent control
of the nematode when planted 1-2
months ahead of the tomato plants as a
rotation crop (Ducusin and Davide,
1972). In the Netherlands it has been
shown that Tagetes spp. can effectively
control root-knot nematodes and other
species when planted either as an inter-
crop or in rotation with other vegetable
crops (Suatmadji, 1969). In the Philip-
pines, however, more studies should be
done along this area as Tagetes spp. can
easily be grown and could cheaply be
used in nematode control if a more prac-
tical method of using it is developed.

>. Influence of nematicides on the develop-
agyne incognita on tomato. Philipp. Agr.

deloidogyne incognita: Its effects on toma-
tilipp. Agr. 55: 261-281.

applied through overhead irrigation on the
,to transplants. Plant Dis. Reptr. 62: 48-51.

; on root-knot nematodes and tomato yield
57: 1033-1035.

grated biological and chemical control of
p. Phytopathol. 12: 9 (Abstr.)
Mr 'Fn _'r M-4- __ -1-+ n-aciftir

Philipp. Phytopathol. 15(2): 145-148
Received for publication: 12 November 1979



Assistant Professor, Department of Life Sciences, University of the Philippines Los
Banos, College, Laguna.

Portion of the Ph. D. dissertation presented by the author to the Graduate School,
Pennyslvania State University, 1976.


Aflatoxin production and growth of Aspergillus parasiticus Speare
NRRL 5835 in potato dextrose broth (PDB) at different propionic acid and
ammonia levels at different pHs (4, 7 and 9) was studied. No growth and
aflatoxin production was detected in PDB having an initial pH of 4 and 7
with acid levels of 1.0% and up and with ammonia levels of 0.2 and 0.1% and
up for pH 7 and 9, respectively.

The solution to the aflatoxin problem
lies mainly on the control of the growth
of the organism. Chemicals, such as am-
monia and propionic acid have been used
to a large extent in Lhe preservation of
grains and other food commodities
against spoilage molds. The value c
ammonia in controlling microbial growth
in citrus fruits has been described by a
number of investigators (Eaks et al.,
1958; Grasovsky and Shiff, 1934: Hop-
kins and McCormack. 1957: Tomkins
and Trout, 1931).
Recently, ammonia was used to pre-
serve stored high-moisture corn against
fungal invasion (Bothast. 1973: Dalma-
cio and Fung, 1977). Propionic acid was
reported to be toxic to a number of
molds (Kosakiewicz and Clarke, 1973)
and has been used to treat feed grains
prior to storage (Sauer. 1972).
Previous laboratory studies conducted
b\ the author in 1976 shower that as lo

as 0.1% ammonia at pH 9. and .1% pro-
pionic acid at both pHs 4 and 7 prevented
aflatoxin production of a toxin-produc-
ting strain of Aspergillus parasit'cis (Dal-
macio, unpublished data).
This study was conducted .: dt-r-
mine the effect of the above (iemincals
on the growth and aflatoxin pr auctionn
of A. parasiticus NRRL 5835 at iif: erent


Potato dextrose broth (PDB) adjusted
to pH 4, 7 and 9 were prepare d using
0.01 M buffer solutions. Levels of pro-
pionic acid and ammonia used were
as follows:
For pH 4 0, 0.01, 0.1, 1.0 1.5 and
2.0% propionic acid
For pH 7 0, 0.01, .,1. 1IC, 1.5
and 2.0% propionic acid
0.0!.0.1 and 0.2% anunonim

ana rropionic Aci On on

For Ph 9 0.0.01, 0.1, 1.0, 1.5 and
2.0% ammonia

One ml spore suspension (approxi-
mately 87,000 spores) of a 2-week old
culture of the isolate was seeded to 75
ml of PDB contained in 250-ml screw-
capped flask and incubated under room
conditions (28 C on the average) for
8 days. A coulter counter model B (Coul-
ter Electronics, Hialeah, Florida) was
used to determine the number of spores
in the suspension. Three flasks were
used per treatment. At the end of the
incubation period, the cultures were
steamed to kill the fungus. Aflatoxin
extraction and thin-layer chromatography
procedures of Pons et al. (1968) and Pons
and Goldblatt (1965). respectively, were
followed. The amounts of aflatoxin pro-
duced by the fungus in the different
treatments were determined.


The amounts of the different aflatoxin
types produced by Aspergillus parasiticus
under different ammonia and propionic
acid levels are in Table 1. The highest pro-
duction of the aflatoxins occurred at
pH 4 with 0.01% propionic acid and at
pH 7 with 0.01% and 0.1% acid. No afla-
toxins were produced at pH 4 and pH 7
with propionic acid concentrations of
1.0% and above, at pH 7 with 0.2%
ammonia and at pH 9 at 0.1% ammonia
and above. The combination of 0.1% am-
monia + 0.1% propionic acid at pH 7
yielded aflatoxins in the amounts similar
to that of 0.1% ammonia at pH- 7. More
aflatoxin G than B were produced at pH
4 with 0.01% propionic acid, pH 7 with
0.01 and 0.1% propionic acid and with
0.01% ammonia and at pHl 9 with 0.01%
Propionic acid and :11immll ia in sinmll

tion by A. parasiticus NRRL 5835 as
shown in Table 1. More aflatoxin was
produced in media with initial pHs of 4
and 7 when 0.01% propionic acid was
added to the medium while addition of
0.01% ammonia enhanced aflatoxin pro-
duction in media with initial pH of 9.
Addition of 0.1% acid to PDB with initial
pH of 4 reduced the growth and aflatoxin
production. A combination of ammonia
and propionic acid at pH 7 markedly re-
duced the aflatoxin production compared
to that in ammonia or acid alone.

The effect of initial pH on aflatoxin
production by A. parasiticus NRRL 2999
in a semi-synthetic medium was examined
by Buchanan and Ayres (1975). Their
data showed that maximal growth, afla-
toxin production and aflatoxin produc-
tion per unit of growth occurred at initial
pH levels of 5.0, 6.0, and 7.0, respective-
ly, and that initial pH levels less than 6.0
favored production of the B toxins,
whereas levels higher than pH 6.0 favored
production of the G toxins. In the
present study, the production of the dif-
ferent aflatoxin types was not influenced
by the initial pH, but probably by the
presence of the chemicals in the medium.
Varying amounts of the B and G aflato-
xins were obtained in the PDB with the
same pH but with different amounts
of ammonia or propionic acid.

The difference between the results
of the present study and the study made
by Buchanan and Ayres (1975) further
substantiates their previous observation
that initial pH has no universal effect
on aflatoxin production and that the
effect of pH is dependent on the com-
position of the medium employed lor
growth of the mold.

The inhibition of the atllatoxiln nni-


hilionine Phytopai

Table 1. Effect of propionic acid and ami
of Aspergillus parasiticus NRRL.

Chemical Concentration (%)
Propionic Re
pH Acid Ammonia Gi

4 0 0 +
0.01 0 +
0.1 0 +
1.0 0
1.5 0
2.0 0
7 0 0 +
0.01 0 +
0.1 0 4
1.0 0 -
1.5 0
2.0 0
0 0.01 4
0 0.1 4
0 0.2
0.1 0.1 4
9 0 0 4
0 0.01 4
0 0.1
0 1.0
0 1.5
0 2.0

a/ No growth
+ Scanty growth
+++++ Most abundant growth
/ Average of 3 replicates
c/ Not detected

tion was primarily due to the inhibition
of A. parasiticus growth. In this experi-
ment, media without any detectable
aflatoxins did not show any A. para-
siticus growth and those with the high-


spoilage molds in corn. J. Dairy Sci.

tion. Appl. Microbiol. 30: 1050-1051

lia on the growth and aflatoxin production

Amount of aflatoxin (ppb)bl
tha/ B1 B2 GI G2

500 50 400 100
F+ 1000 200 1400 350
250 50 200 50
750 150 700 175
-+ 1000 200 1400 350
-+ 1000 200 1400 350
750 150 1200 300
250 50 200 50
50 200 200 50
S 500 100 500 125
-+ 100 200 1200 300

est amounts of the toxins had the most
growth. It is very possible that the treat-
ments used in this research could inactive-
ate aflatoxin, however, detoxification
under these conditions were not studied.


,.W. HESSELTINE. 1973. Ammonia kills

75. Effect of initial pH on aflatoxin produc-



anu rropionlc AnCi on t

ed with "cold flow" ammonia. Kalika

control of Rhizopus rot on peaches. I

GRASOVSKY, A. and M. SHIFF. 1934.
storage of oranges. Hadar 7: 168.

board carbons on stem-end rot and n
20: 18.

of propionic acid to fungi from store(

1968. Improved fluorodensitometri
products. J. Amer. Oil Chem. Soc. 45

PONS, W.A. Jr. and L. A. GOLDBLATT. 1
tion of aflatoxins in cottonseed prc

SAUER, D. B. 1972. How to use organic
and Mycotoxins. Agri. Fieldman 28:

TOMPKINS, R.G. and S.A. TROUT. 1931
the prevention of green mold in citru

, Philipp. J. Biol. 6: 203-216.

CHER. 1958. Ammonia gas fumigation for
tDis. Reptr. 42: 846.

effect of ammonium bicarbonate on the

,7. Effect of ammonia treatment on fiber-
decay in Florida oranges. Fruit. Veg. Mag.

173. Techniques for determining toxicity
tin. Trans. Br. Mycol. Soc. 61: 355-367.

determination of aflatoxins in cottonseed

. Improved flourodensitometric determina-
Its. J. Amer. Oil Chem. Soc. 42: 461-475.

s for best results. Master Manual on Molds

ke use of ammonia and ammonium salts for
Hort. Sci. 9: 257.

Philipp. Phytopathol. 15(2): 149-156
Received for publication: 4 December 1979



Research Assistant and Assistant Professor, Department of Plant Pathology; and
Instructor, Department of Horticulture, respectively, U.P. at Los Banos, College, Laguna.


One hundred ninety six cowpea selections were screened against Fusa-
rium wilt and dry root rot complex under field conditions. Three selections
were moderately resistant, 23 moderately susceptible and 170 as highly sus-
The moderately resistant cowpea selections were P.L 170844, 180013
and 293453 while the moderately susceptible selections were P.I. 293455,
182316, 293171, 146113, 164337, 295570, 205240, 292906, 293497,
256341, 4544, 433, 346, TVU. 1065-1, 1707-1, 1778-1, 45, 1009-1-1, 1035-
1, 1283, 1438, 30-1-1 and VCS 6-1.

The organisms isolated from the infected cowpea plants were identified
as Fusarium oxysporum Schlect and Fusarium solani (Mart) Appel.

Cowpea, botanically known as Vigna
unguiculata (L.) Walp. [V sinensis
(Tomer) Savi ex Hassk., V cylindrica
(L.) Skeels is considered one of the
economically promising crops in the
Philippines. This herbaceous plant under
Family Leguminosae provides a cheap
source of vegetable protein. It is also a
good source of minerals and vitamins
for our body's needs. Furthermore, the
mature dried pods of cowpea can be uti-
lized as feed by poultry and livestock.
As a legume, it can be used as green
manure when cultivating other crops.

Growing cowpea is a profitable one;
in fact, it is an important item of com-
merce and a good monej maker. In one
cropping, from May to July, a farmer can

get as much as P 4,000 per hectare.
Marketing is not a problem and the
prices do not fluctuate much. Jamora and
Sarian (1975) reported that a Japanese
firm has already expressed interest to
import several hundred tons of red beans
from the Philippines. An increase in the
commercial production of the crop will
meet the local and fast increasing foreign

Despite the advancement made in the
production and marketing aspects of this
commodity, diseases have limited its
potential yield. Among these diseases,
the most common and destructive are
probably the wilt and dry root rot.

As early as 1899, Fusarium wilt

by E.F. Smith of the USDA Division of
Vegetable Physiology and Pathology. The
result of subsequent extensive investiga-
tions shed light on the cause of the
disease, the nature, biology and relation-
ship of the fungus inciting it. In 1902,
Orton published a rather comprehensive
account of the same disease.

On the other hand, Fusarium root rot
was first investigated by W. H. Burkhold-
er in Western New York in 1915. He
mainly studied the histopathology of root
rot diseases, but did not report on the
mode of penetration.

Barker and Neal (1923) stated that
wilt was the most serious disease of cow-
pea in Mississippi. Kendrick (1929)
observed that 90% of the cowpea had
been killed by Fusarium wilt in a study
done in San Joaquin Valley, Califonia.
He noted that of the 74 selections used
in the field tests, only 7 were apparently
immune and all the rest were susceptible.
Johnston (1963) reported that Fusarium
wilt organisms caused spreading lesions,
killed parts and affected the growth of
cowpea in Hongkong.

Burkholder (1917) observed that in
New York State, Fusarium root rot
disease is of general occurrence. It has
been observed in 90% of the bean fields
in the six largest bean producing countries,
and is found wherever the crop has been
grown. Weimer and Harter (1926)
observed that root rot of bean is a wide-
spread disease in California. The per-
centage of plants affected varied consi-
derably, not only in different fields but
also in different parts of the same field.
Some entire fields have been seen where
practically 100% of the plants were
affected. Chatterjee (1958) reported that
the disease is considered to be the major

state of Idaho. It is so prevalent that it
is almost impossible to find a non-infect-
ed plant growing in the major bean pro-
ducing areas.

In order to reduce crop damage, the
use of resistant varieties seems the most
economical and practical measure of con-
trolling the disease. In USA, Hare (1949)
showed that generally,the cowpea varie-
ties like Black Crowder, Red and
Speckled types were relatively resistant
to Fusarium wilt. Erwin and Thomason
(1956) found that the Grant variety of
Blackeye was relatively resistant to Fusa-
rium wilt in a study done at the Univer-
sity of California.

Regarding the susceptible varieties,
Mackie (1934) observed that the Black-
eye cowpeas in the Interior Valleys are
liable to severe damage by Fusarium wilt.
Singh (1954) found that the new early
maturing variety of Lobia type was
suffering from a wilt disease in India.
For Fusarium root rot disease, the pro-
duction of resistant varieties has not been
satisfactorily done due to lack of highly
resistant breeding material (Zaumeyer
and Thomas, 1957). However, they point-
ed out that crop rotatioa\ith cereals has
proved the most sum=es and effec-
tive means of control.

On the identity of the causal organism,
Oyekan (1975) claimed that the cowpea
wilt is caused by Fusarium oxysporum f
sp. trcheiphihum in Ibadan, Nigeria. This
confirmed an earlier woa by Singh and
Singh (1955) who stayed that Fusarium
oxysporum f. sp. tracheiphilum indeed
caused cowpea wilt. Schroth and Snyder
(1961) on the other hand claimed that
Fusarium solam (Mart) Appl. & Wr. f. sp.
phaseoli causes the root rot of cowpea.
The fungus normally attacks the bean

ialippine rhytopat


In the Philippines, studies on tt
screening of cowpea varieties again
Fusarium wilt and dry root rot have nc
yet been done. Hence, there is an imper;
tive need to locally evaluate cowpe
selections for resistance against Fusi
rium wilt and dry root rot. A method c
evaluating the resistance of cowpea selei
tions is by screening them under fiel
conditions in a heavily infested are,

This experiment was conducted at tt
College Experiment Station (CES) ne;
the Rodent Research Center and the D
apartment of Plant Pathology, U.P. at L<
Banos. The aims were: 1) to determir
the resistance or susceptibility of sever;
cowpea selections against Fusarium wi
and dry root rot under field condition
and 2) to verify the identity of the Fus,
rium species causing wilt and dry roc
rot on cowpea in the Philippines. Th
field and laboratory studies were carrie
out from June, 1977 to April, 1971


Cowpea selections tested, planting c
seeds and inoculation. One hundred nine
ty six selections were used in the stud)
They were sown at the CES in an area c
20 m x 10 m with an average of 20 seed!
row which were further thinned aft(
seedlings have emerged leaving out 1
plants/row. The experiment was replica
ed twice.
The plants had natural inoculation
of Fusarium species which are widely:
distributed in the test soil..

Quantitation of Fusarium spp. in th
soil. To determine the inoculum poter
tial of the pathogen, fifty soil sample
were collected at random in the are,
Twenty five samples were collected fror

nearby root zone. Soil samples of abo
5 grams were collected, placed in plast
bags and labelled with the date and si
of collection. The soil samples we
brought to the laboratory, weighed fi
sub-samples and tested for the prescne
ofFusarium spp. propagules.

Direct inoculation method of fun
from soil was used (Waksman, 1916
Crumbs of soil were pulverized and tran
ferred aseptically with sterile forceps c
the center of the PCNB agar medium
with streptomycin (Papavizas, 1967) i
petri dishes. Soil samples weighing 0.C
and 0.1 grams were spread evenly on tf
plates. This experiment was replicate
thrice. The discs were covered and ii
cubated for 24 hr at 20 C. Fusariui
propagules were observed and quantifie
with the use of colony counter.

Disease evaluation and classification e
reaction. Plants were evaluated week
for the presence of Fusarium infection
from 3 weeks time after their cme
gence from soil up to the fruiting stagi
Criteria used were crop growth, absence
or presence and development of Fus;
rium wilt and dry root rot. A weekly ev;
luation was made starting July 8, takin
note of the total number of seedlings pc
row and the number of infected or wilte
plants. A representative plant in a rol
was considered infected when the sign
and symptoms of Fusarium wilt and dr
root rot were shown. The results wer
expressed in percentage of infected
plants, obtained by dividing the number
of infected cowpea plants by the tote
number of plants in each row, then mul
tiplied by 100. The average of the tw,
replicates represented the reaction of
the selections.

In classification of reaction, a mod


June 1979 Screening for Fusarium Wilt 152

fled disease index was devised to deter- medium, hyphal growth of pure cultures
mine the promising selections. were scraped and observed in the com-
pound microscope. Identification of the
The infection ratings were as follows: causal organism was based on the mor-
Percentage of Reaction phological and cultural characteristics.
Infected Plants The morphological characteristics exam-
ined were the sizes, shapes and septations
0 Highly Resistant or Immune (HR) of macroconidia and microconidia, pre-
1-15 Moderately Resistant (MR) sence or absence of chlamydospores and
16-30 Moderately Susceptible (MS) spore measurements. One hundred micro-
31-above Highly Susceptible (HS) conidia and 150 macroconidia were
measured for each type of pathogen
Microscopic observation and patho- isolated. Cultural characteristics exam-
gen isolation. The infected cowpea plants ined included the manner and rate
in every row were carefully uprooted of growth, sporulation and the color
and labeled with the date of collection exhibited in pure cultures. Growth
and selection number. Then they were rates and sporulation were assessed after
observed under the compound micros- 4 days on 100 plates for each particular
cope for detailed symptoms and the pre- species.
sence of Fusarium wilt and dry root rot
causing organisms in the roots, base of RESULTS AND DISCUSSION
stems, cortex and vascular elements of
the plants. Description of signs and symptoms
of the disease
For isolation, the discolored diseased
tissues were washed under running tap Fusarium wilt
water to remove surface dirt. Two to
three sq. mm were cut from the ad- The uprooted infected cowpea plants
vancing area of the lesions in such a way showed a faint reddish-brown to dark
that the specimens included both healthy tinge in the stem. Sectioned stem show-
and diseased portions. The diseased parts ed the dark brown discoloration of the
were surfaced-sterilized in 1% sodium vascular system which extended through-
lmnnhlnrita f-nr -1- m-n than rinpda in .llt the nl2nt Thp latpral rnntc wilted

ess of transfer. Sections were then placed
I sterile blotting paper. To prevent bac-
erial contamination, two-three drops of
% lactic acid were dropped during
lating, then dried for 12 hr at room
;mperature. Four to five sections were
quidistantly placed in plated PDA.

Identification of pathogen species.
'ure cultures were grown in diffussed
lay light for 20 days, then maintained at
O"C. After mvcelia radiated on the agar

Dropped from the stem.

'usarium root rot

The first visible symptom showed by
he infected cowpea plants was the red-
lish discoloration of the taproot which
gradually intensified and eventually
turned brown. The feeder and lateral
oots rotted; soon, adventitious roots
appeared on the upper part of the tap-
root. Yellowing and drooping of the

Philippine Phytopathology

foliage was exhibited but pronounced
wilting was occasionally observed. Also,
the infected plants appeared stunted.
Aside from the characteristic symp-
toms exhibited by the plant with above
diseases, white cottony mass of mycelia
grew on the surface of the stems. The vas-
cular and cortical tissues also had patho-
gen growth, and sometimes caused their
walls to become deeply stained and
Source of infection and quantitation
of Fusarium in soils. The experiment in
the field depended on natural inoculation
as source of infection for the standing
cowpea plants. Seeds used were devoid
of anti-fungal chemicals. The infection
observed was the natural reaction of the
selections to seed or soil-bore Fusarium
spp. Kendrick (1931) reported that the
fungus is transmitted on the seeds espe-
cially where machine methods were used
in harvesting. Armstrong and Armstrong
(1950) also reported that transmission of
the pathogen was through soil and seeds.
Soil samples plated in improved PCNB
medium showed white cottony growth
after 24 hr at 200C. Hyphal tips when
transferred and microscopically examined
on a slide revealed abundant chlamydos-
pores which occurred singly and in pairs
and varied in sizes, shapes and wall

The quantified propagules of Fusa-
rium in the experimental area as deter-
mined by plate counts showed an in-
creasing trend with the soil sample
weight. The average number of propa-
gules quantitated per gram soil was 1,531.
The distribution of Fusarium spp.
within the field was remarkably uniform.
The fungus Fusarium solani f. sp. pha-
scoli or other species of Fusarium may
occur in the form of chlamydospores
(Nash, et al. 1961). The ability of Fusa-

rium species to form chlamydospores is
important in their survival and as source
of infection for the standing crop. The
fungus is usually associated with the soil
and gain entrance through the root sys-
tem of the plants and then cause the
brown discoloration of the vascular sys-

Reactions of cowpea selections. The
screening of cowpea for Fusarium wilt
and dry root rot resistance showed 3
selections to be moderately resistant and
23 moderately susceptible to these
diseases. The moderately resistant selec-
tions were Plant Introduction (P.I.)
numbers 170844, 180013 and 293453
while the moderately susceptible selec-
tions were P.I. 293455, 182316, 293171,
146113, 256341, 164337, 295570,
205240, 292906, 293497, 4544, 433,
346, TVU 1065-1, 1707-1, 1778-1, 45,
1009-1-1, 1035-1, 1283, 1438, 30-1-1
and VCS 6-1.
The other remaining selections were
highly susceptible. No selection was
found to be highly resistant or immune
to these diseases. Table I shows the num-
ber of infected plants, percentage infec-
tion and reaction of the moderately re-
sistant and moderately susceptible ones
among the 196 selections.

The cumulative percentage infection in
the field test was noted between 3-10
weeks of evaluation. The percentage of
infection varied among the different
selections during the weekly assessments.
The cumulative percentage showed that
infection tremendously increased during
the 5th week up to the 9th week with the
latter coinciding with flowering and pod
formation. Thomas (1938) reported that
the incidence on red grains (V. unguicu-
lata) steadily increased from the 5th
week after emergence, reached a peak
between the 13th and 15th week, then

Vol. 15

'ening for Fusarium Wilt

Table 1. Moderately resistant and moderated
number of infected plants and percel

No. of infected
Selections Replicate Tota
1 2

PI 170844 1 1 2
*180013 1 1 2
293453 1 2 3
293455 4 0 4


sceptible selections with corresponding
? infection

Mean infection Reaction

1.0 10 MR
1.0 10 MR
1.5 15 MR
2.0 20 MS
2.0 20 MS
2.0 20 MS
3.0 30 MS
2.5 25 MS
2.5 25 MS
3.0 30 MS
2.5 25 MS
2.0 20 MS
2.5 25 MS
2.5 25 MS
3.0 30 MS

MR Moderately Resistant
MS Moderately Susceptible

:lined. Also, a great percentage of the
dlings got infected after emergence
led on the 4th week of evaluation.
nerally, percentage infection decreased
the plants aged. The degrees of infec-
n were severe in highly susceptible

Description and identification of
hogen species. Based on the taxono-
: system of Snyder and Hansen (1940)
isolated and identified organisms
m the experimental area were Fusa-
m oxysporum Schlect and Fusarium
ani (Mart) Appel. The former belongs


the Martiella group. and measured at an average of 9.35 x
3.67 u.
Fusarium oxysporum Macroconidia developed from short
multi-branched conidiophore which soon
Microconidia were abundant and most- emerged to form sporodochia. The apical
ly unicellular. They were ovoid-fusoid to cell was somewhat beaked and foot cell
ellipsoidal in shape, and were borne on was rounded with thicker walls. They
short lateral conidiophores. They mea- were usually fusoid and with 4-6 septa-
sured at an average of 7.02 x 3.62 tions whose sizes ranged from: for 4
Macroconidia were usually formed septations, 28.75 x 3.42 u; 5 septations,
from sporodochia. They were bigger and 31.72 x 3.49 u; and 6 septations, 32.06
elongated, usually with thin walls and x 4.42 u. The average size of the 150
finely pointed at their extremities. They macroconidia was 30.83 x 3.76 P.
had from 3-5 septations when mature Chlamydospores were abundant and
and ranges in measurements were: for 3 usually formed singly and in pairs. They
septations, 34.29 x 3.72 u; 4 septations, were either boe terminally or inter-
46.43 x 4.39 .u; and 5 septations, 52.84 x c
4.65 u. The average size of the 150
macroconidia was 44.52 x 4.25 )a. Growth on PDA was at the average of
s we a t ad 3.52 cm diameter after 4 days, and sparse
Chlamydospores were abundant and
Pr I lV formed singly or in airs. to dense. It produced many color varia-
wi/re iinually formpri sinolv or in nairs-

6516 6uf j a' uruI forj wiLL

NDRICK, J. B. 1929. Susceptibility of cowpea varieties and selections to Fusarii
wilt and root knot. Phytopathology 19: 1145 (Abstr.).

21: 979-983.

CKIE, W. W. 1934. Breeding for resistant
charcoal rot and nematode. Phytopatholh

.LER, J. J. 1946. Cultural and taxonomic

SH, S. M., C. CHRISTOU and W. C. SNY
f. sp. phaseoli as chlamydospores in soil.

TON, W. A. 1902. The wilt disease of cow'
Indus. Bul. 299 p.

EKAN, P. O. 1975. Occurrence of cowpe
sp. tracheiphilum in Nigeria. Plant Dis. E

PAVIZAS, G. 1967. Evaluation of various
tion of Fusarium in soil. Phytopathology

BROTH, M. M. and W. C. SNYDER, 1961.
germination of the bean root rot fungi
pathology 51: 389-393.

IGH, R. S. 1954. Wilt of Lobia in Uttar Prai

IGH, R. S. and R. P. SINGH. 1955. Studio
I. Occurrence and symptoms of the di
J. Indian Bot. Soc. 34: 375-385.

YDER, W. C. and H. N. HANSEN. 1940.
J. Bot. 27: 64-67.

if Blackeye cowpea to Fusarium wilt,
24: 1135.(Abstr.)

lies on certain Fusaria. Can. J. Res. 24:

R. 1961. Existence of Fusarium solani
topathology 51: 308-312.

and its control. U.S. Dept. Agr. Bu. P1.

'ilt caused by Fusarium oxysporum f.
r. 59: 488-490.

dia and anti-microbial agents for isola-

ect of host exudates on chlamydospore
Fusarium solani f. sp. phaseoli. Phyto-

i. Sci. Cul. 19: 454-480.

n the wilt of cowpea in Uttar Pradesh.
e and identity of the causal organism.

e species concept in Fusarium. Amer.


rnuippine rnyropatnoogy

Veg. Phy. and Path. Bull. No. 17.

THOMAS, R. S. 1938. Detailed Admih
Madras. 21 pp.

WAKSMAN, S. A. 1916. Do fungi 1

by Fusarium martii phaseoli Bu

study of bean diseases and met]

ration Report of the Government Mycologi

and produce mycelium in soil? Science, N

16. Root rot of the bean in California caul
ind Fusarium aduncisporum. J. Agr. Res.

S. 1957. Fusarium root rot. In a monogram
a for their control. U.S.D.A. Tech. Bull. 8(




Assistant Professor and Senior Research Assistant, respectively, Department of
ant Pathology, University of the Philippines at Los Banos, College, Laguna.

Based on a study supported by National Research Council of the Philippines (NRCP

Stevens and Celino (1930) first report- consisting of brown rings alternating with
I a leafspot of papaya (Carica papaya light brown areas (Fig. 1B). Both young
) in the Philippines and named the and mature leaves are infected. The entire
,usal agent as Helminthosporium papaya leaf turns yellow before the leaf falls.
rd. The identification was based on des- On flowers. Spots on the flowers are
options given by Sydow (1923) from circular and light brown at an early stage,
materials collected from Zamboanga, becoming irregular as they enlarge. Spots
indanao, Philippines. In 1950, Wei coalesce and form bigger blotch until
.amined the type materials deposited at the whole flower is involved (Fig. 2).

ilipp. Phytopathol. 15(2): 158-161

Philippine Phytopathology

Corynespora casiicola. This was reported
to be the causal agent of "greasy spot
or papaya decline" in St. Croix, U.S.
Virginia Islands (Bird et al. 1966) and has
also been reported in Puerto Rico (Melen-
dez and Pifero, 1971) on papaya leaves,
and in Barbados (Norse, 1973), on stems
and fruits. It all indicates that the pre-
sent strain in the Philippines is more

destructive since it infects all parts of
the papaya tree except the trunk. A long
list of hosts had been reported for Cory-
nespora casiicola (Ellis, 1957) indicating
apparent importance of the organism as
a disease agent. For this reason, studies
on its pathogenicity and host range
among Philippine plants will soon be

Fig. 1. A. Pinpoint chlorotic spots on papaya leaves caused by Corynespora casiicola. B.
Close-up of mature spots showing distinct zonation of dark and light brown

Vol. 15


ig. 2. Healthy (left and middle) and Fig. 3. Papaya fruit showing circular, dark
diseased (right) papaya flowers. sunken spots caused by C. casiicola.

II- .~....^^Cn


161 Philippine Phytopathology Vol.


Fig. 5. A. Conidiophores of Corynespora casiicola in tuft emerging from the ho
surface. B. Conidium borne singly at tip of conidiophore. C. Conidia from c


BIRD, J., A. KROGHMAL, G. ZENTMYER & J. ADSUAR. 1966. Fungus diseases
papaya in the U.S. Virginia Islands. J. Agr. Univ. Puerto Rico 50: 186-200.

ELLIS, M. B. 1957. Some species of Corynespora. Mycol. Papers No. 65, Comm
wealth Mycol. Inst. Kew, Surrey. 15 p.

WEI, C. T. 1950. Notes on Corynespora. Mycol. Papers No. 34, Commonwealth My(
Inst., Kew, Surrey. 19 pp.

MELENDEZ, P. L. & J. B. PINERO. 1971. Corynespora leafspot of papaya (Car
papaya L.) in Puerto Rico. J. Agr. Univ. Puerto Rico 55: 411-425.

NORSE, D. 1973. A stem and fruit disease of papaya in Barbados caused by Co
nespora casiicola. Plant Dis. Reptr. 57: 404-406.


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