Genetical Relatedness of a Former Apomict and a Heterothallic Isolate in Didymium Iridis (Myxomycetes)

ABSTRACT

Several lines of the Pan 4 isolate of Didymium iridis (Ditmar) Fries have been made to convert from an apomictic to a heterothallic life cycle mode. With the single exception of the Ky 1 isolate, clones from the converted lines are either incompatible or only partially compatible with all available naturally occurring heterothallics. This indicates that during its existence as an apomict Pan 4 diverged from those heterothallic counterparts to the point where it is now reproductively isolated from them. In the case of the Ky 1 isolate, however, sexual compatibility is relatively good. This is especially intriguing because Ky 1 is incompatible with all other known heterothallics. Analyses of Pan 4 × Ky 1 F₁ hybrids show that recombination did occur, as evidenced by recovery of both parental mating types, by segregation of two vegetative (plasmodial) fusion classes, and by increased sexual compatibility in crosses of F₁'s x parents as compared to parent x parent. These results show that Pan 4 and Ky 1 are more related to each other than each is to any other isolate. Whether mating types of these two isolates constitute a separate multiple allelic series remains somewhat uncertain, however, because of partial barriers between Pan 4 and Ky 1.

Key Words:

• apomixes
• heterothallism
• genetical divergence