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 possessed cultural growth characteristics and morphologies similar to P. ultimum var. ultimum produced antheridia and mated successfully when paired with self-fertile (type O or homothallic) isolates of this species and P. ultimum var. sporangiiferum. The self-sterile isolates produced antheridia that fused with oogonia produced by self-fertile isolates of P. irregulare but the oogonia aborted. The self-sterile isolates were identified as male forms of P. ultimum, since they exclusively formed antheridia when paired with self-ferile isolates of this species. Progenies from crosses between male and self-fertile isolates displayed traits of recombination in culture, indicating normal sexual reproduction occurred during mating.