Gametangial meiosis in Phytophthora capsici

Abstract

The report of Stephenson et al. that the nuclear divisions in the gametangia of Phytophthora capsici are mitotic, resembling the divisions in the vegetative hyphae, was not confirmed. Pachytene, diplotene, and diakinesis stages were observed in the oogonia. Metaphase and anaphase were followed by a second division without any increase in nuclear and chromosome size between the two divisions. The haploid chromosome number is nine and an association of four chromosomes is present in one or both parents.The association of four chromosomes observed at diakinesis and metaphase is evidence that pairing of homologous parts occurs during the first division and is thus proof that the gametangial divisions are meiotic.There was no evidence of a prolonged prophase in the first division of the zygote nucleus and an eight-nucleate oospore showed no evidence of reduction in nuclear size or nuclear elimination such as would be required to account for the homokaryotic condition of single-oospore cultures on the hypothesis of zygotic meiosis.The problems involved in obtaining reliable chromosome counts from somatic nuclei are discussed.