280 M. BABADOOST
Pseudoperonospora cubensiscan infect cucurbit plants at all ages. Infection is
limited to leaves. Symptoms of downy mildew are small, slightly chlorotic to
bright yellow areas on the upper leaf surface and mold (sporangiophores and
sporangia) ofP. cubensison the corresponding lower leaf surface.Pseudoper-
onospora cubensisis an obligate parasite and thus survives only on living host
tissues. Host range ofP. cubensisis limited to only members of the Cucur-
bitaceae family. Temperatures of 15â25âŚC and moist conditions are favorable
for downy mildew development.Pythiumspp. are soil inhabitants, existing as
nonspecialized parasites.Pythium anandrum,P. aphanidermatum,P. irregular,
P. myriotylum,oligandrum,P. periplocum,andP. ultimumcause damping-off,
root rot, and Pythium cottony leak.Pythiumspp. cause infection in a wide
range of species in more than 24 pant families. Cooler and moist conditions
favor infection byPythiumspp. All of the oomycete pathogens of cucurbits
have been reported from cucurbit-growing areas throughout the world. Under
favorable environmental conditions, these pathogens can cause up to 100%
crop losses. Strategies for effective management of diseases caused byP. capsici,
P. cubensis,andPythiumspp. in cucurbits are different from each other, but
no single method is adequate for successful control of any of these pathogens.
Successful, long-term management of each of the diseases caused by oomycete
pathogens in cucurbits requires integrated strategies with measures that erad-
icate or reduce initial inoculum, reduce effectiveness of primary inoculum,
increase the resistance of the plant, delay the onset of disease, and slow spread
of disease.
KEYWORDS:damping-off; disease management; downy mildew; fruit rot; Phy-
tophthora blight;Phytophthora capsici;Pseudoperonospora cubensis;Pythium
spp.
I.INTRODUCTION
II.OOMYCETES
A.Taxonomic Position of Oomycetes
B.Biology of Oomycetes
C.Classification of Oomycetes
D.Plant Pathogenic OomycetesIII. Oomycete Diseases of Cucurbits and their Management
A.Phytophthora Blight
1 .Symptoms
2 .Pathogen Biology
3 .Host Range
4 .Disease Cycle and Epidemiology
5 .Disease Management
B.Downy Mildew
1 .Symptoms
2 .Pathogen Biology
3 .Host Range
4 .Disease Cycle and Epidemiology
5 .Disease Management