GROUP DISCUSSION 1 Research Needs on the Pathologens

Abstract

Shaw : I will lead off by discussing mating reaction – item 1. There is uncertainty as to where meiosis occurs in the life eyeles of Oomycetes. For years in fungi like the downy mildews (DMs) the nucleus in the oospore was considered diploid (2n) and meiosis was reported to occurduring oospore germination. However, Sansome (Chromosomes Today, V, i: 77-83. 1966) has hyoothesized that all the oomyeetes, including the DMs, may be diploid in their vegetative state. This would mean that meiosis does not occur in the first divisions of the oospore nucleus but occurs in the formation of gamete nuclei i.e. during the last two nuclear divisions in the antheridium and oogonium respectively. The genetic basis for pathogenicity is entirely different if we are dealing with diploid (2n) vegetative mycelium instead of haploid (1n) mycelium. We must clarify the chromosomal and nuclear content of the mycelium of DMs.