SELF-STERILE ISOLATES OF PYTHIUM MATE WITH SELF-FERTILE ISOLATES OF PYTHIUM-ULTIMUM

Self-sterile isolates of Pythium (type S or Pythium group HS) that pos sessed cultural growth characteristics and morphologies similar to P. ultimum var. ultimum produced antheridia and mated successfully when p aired with self-fertile (type O or homothallic) isolates of this speci es and P. ultimum var. sporangiiferum. The self-sterile isolates produ ced antheridia that fused with oogonia produced by self-fertile isolat es of P. irregulare but the oogonia aborted. The self-sterile isolates were identified as male forms of P. ultimum, since they exclusively f ormed antheridia when paired with self-ferile isolates of this species . Progenies from crosses between male and self-fertile isolates displa yed traits of recombination in culture, indicating normal sexual repro duction occurred during mating.