Production of chlamydospores by Fusaria in onion (Allium cepa) bulb extract

Production of chlamydospores by Fusarium oxysporum f. sp. ciceri, F. oxysporum f. sp. lini, F. oxysporum f. sp. lycopersici, F. oxysporum f. sp. pisi, F. semitectum, F. solani and F. udum on cellophane disc on unsterilized sandy loam soil and acid washed sand saturated with onion bulb extract was determined at different temperatures and pH. Onion bulb extract enhanced the formation of chlamydospores from macroconidia of seven species of Fusarium. Chlamydospore production from macroconidia incubated on soil saturated with 0.1% (v/v) steam sterilized (antoclaved) bulb extract or with 0.01% (v/v) Millipore filtered bulb extract was significantly (P = 0.05) greater than on sand. Chlamydospore formation was also significantly (P = 0.05) higher in autoclaved bulb extract than in the extract sterilized by Millipore membrane filter. Chlamydospore initials were formed in maximum frequency after 18 h of incubation and chlamydospore production reached at the peak after 7 d incubation. Higher temperatures (25-45 C) favored the chlamydospore production. Greater production was at 35 C. Chlamydospore production was higher at pH 6-7 and was reduced significantly (P = 0.05) beyond this range. The results indicate that onion bulbs extract significantly increased the chlamydospore production.