Sexuality in Pythium sylvaticum: Heterothallism

SUMMARYPairings of 5 heterothallic isolates of Pythium sylvaticum in all possible combinations revealed the existence of 2 sexually compatible groups of isolates.Tracings of gametangial hyphae leading to the formation of over 100 oospores showed that 3 heterothallic isolates produced only antheridia whereas 2 produced only oogonia.The nature of the line of contact between male and female isolates permitted prediction of the sex of the parental isolates; male and female isolates were found on the smooth and diffuse sides of the reaction line, respectively.Evidence suggestive of a possible hormonal system controlling the initiation of gametangial initials was found.