Chlamydospore Induction in Pure Culture in Fusarium Solani

SUMMARY

Chlamydospore initiation by ungerminated or pre-germinated macrospores of Fusarium solani f. sp. phaseoli is induced by incubation in a complete medium at pH 4.0; this low pH may be achieved by direct adjustment or by changes in the amount and source of nitrogen. Between pH 4.0 and 6.5 the proportion of chlamydospore initials to normal germ tubes falls linearly. Initials form in maximum frequency in 6–12 hr from pre-germinated spores, in 18–24 hr from ungerminated spores. Maximum chlamydospore induction from ungerminated spores requires sources of carbon, nitrogen, and minerals; induction from pre-germinated spores has only a partial carbon requirement and no requirement for nitrogen or minerals. Pre-germinated spores can form chlamydospore initials under anaerobiosis, ungerminated spores cannot. Induction from ungerminated spores is independent of spore concentration over the range 2.5-1,000 × lO³ml. The pH effect on induction is not attributable to a deficiency of exogenous phosphate. Developmental alternatives for ungerminated and germinated spores are described; these are subject to experimental control.