CONTINUING VARIATION IN SUCCESSIVE ASEXUAL GENERATIONS OF PYTHIUM SPLENDENS FOLLOWING SEXUAL REPRODUCTION

Stability of the phenotypic characteristics of growth rate, colony typ e, sensitivity to streptomycin and sensitivity to chloramphenicol of t he conidium progeny of selfed oospore cultures of Pythium splendens wa s investigated. Progeny were divided into parental A type, D type for those deviated from A type but with uniform pattern and M type for tho se with irregular growth pattern or with dissimilar appearance on two replicate plates. Conidium progeny of A type isolate 167F and its A ty pe oospore cultures showed the same colony type and displayed little v ariation in growth rate, and sensitivity to streptomycin and chloramph enicol. The D and M type oospore cultures displayed considerable varia tion in all phenotypic characteristics measured. Similar variation in conidium progeny following selfing was observed in isolate 167F-9, an A type oospore progeny of isolate 167F. Following sexual reproduction conidium progeny continued to vary in second and third conidium genera tions tested. The phenomenon of continuing variation in successive ase xual generations induced by sexual reproduction may plan an important role in evolution, survival and development of pathogenicity and fungi cide resistance of an organism by increasing the diversity and extent of the constitutive variation resulting from gene recombination during sexual reproduction.