A new isolate of Sclerotium rolfsii Sacc. causing bulb rot in onion (allium cepa L. variety Poona red)

The causative fungus of a hitherto unreported bulb rot cusease of onion (Allium cepa L. variety Poona red) was found to be Sclerotium rolfsii Sacc. The vegetative propagative structures of the fungus known as sclerotia, were able to germinate within 24h on a suitable substratum and produce new colonies. The fungus took about ten days to produce fresh sclerotia from germinating sclerotia, under laboratory conditions. The fungal isolate obtained from infected onion plants (Sclerotium rolfsii - Isolate 5) had a temperature optimum of 35% for germination of sclerotia. It showed luxurious growth and maximum amount of sclerotial production at temperatures between 30 and 35⁰ C. The fungus was able to survive in a wide range of pH conditions (pH 3 to 9) but had an optimum pH of 5.5 for germination of sclerotia and radial growth.