STUDIES ON Colletotrichum gloeosporioides (Penz.) Penz and Sacc. THE CAUSAL AGENT OF LEAF SPOT OF CASHEW (Anacardium occidentale L.)
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Date
2001
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University of Agricultural Science, Dharwad
Abstract
"Studies on Colletotrichum gloeosporioides a causal agent of leaf spot of
cashew (Anacardium occidentale L.) includes sun-ey of the disease spread,
morphological, physiological, nutritional studies, spore germination, toxin
studies, host range studies and in vitro evaluation of chemicals and
botanicals.
During survey in three districts the maximum mean per cent disease
index was found to be 17.10 in Sirsi. The fungus was isolated from infected
cashew leaves. The pathogenicity was proved by spraying monoconidial
culture which resulted in the formation of numerous oval or irregular brown
or deep brown spots of variable sizes and shapes were noticed. The conidia
were cylindrical or oblong, hyaline single celled with oil globules in the
centre and measured about 8.2 to 10.34 x 3.4 x 4.5 ;Um. Spores germinated
with varied number of germtubes originated from any surface of the conidia.
Among various media tested maximum spore germination occurred in two
per cent sucrose solution. Potato dextrose agar and Richards's broth were
best solid and liquid media respectively which supported maximum growth
of the fungus. Sucrose, potassium nitrate and magnesium sulphate yielded
maximum dry mycelial weight of the pathogen among the carbon, nitrogen
and sulphur sources respectively. Maximum growth of fungus was recorded
at 6.5 pH and 30°C temperature. Maximum toxic metabolite was produced
when sucrose, potassium nitrate and magnesium sulphate were used as
carbon, nitrogen and sulphur sources, respectively. The pathogen showed
positive reaction on all the host tested. In vitro evaluation of fungicides and
botanicals revealed that carbendazium (500, 1000 and 1500 ppm) and
garlic bulb extract (5 and 10%) were effective against C. gloeosporioides
respectively. Among different cultivars tested, Vengurla-1 showed resistant
reaction for leaf spot of cashew under artificial condition."
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