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Genetics

Heterothallism in Peronospora effusa. T. Inaba, Plant pathologist, Division of Plant Pathology, National Institute of Agricultural Sciences, Yatabe, Tsukuba, Ibaraki 305, Japan; T. Morinaka, plant pathologist, Division of Plant Pathology, National Institute of Agricultural Sciences, Yatabe, Tsukuba, Ibaraki 305, Japan. Phytopathology 74:214-216. Accepted for publication 2 September 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-214.

Nineteen isolates of the spinach downy mildew pathogen, Peronospora effusa, were collected from spinach seedlings infected by seedborne oospores. The isolates were subcultured individually in spinach cotyledons for 6- 15 mo, and no oospores were detected. Although inoculation with single isolates did not result in oospore production, oospores were observed in cotyledons inoculated with certain specific pairs of isolates. The isolates were grouped into two mating types; crosses within each group were sterile, whereas those between the groups were fertile. Seventeen isolates belonged to the mating type P1 and two isolates to the mating type P2. Antheridia were declinous, paragynous, and single. These results clearly demonstrate the existence of heterothallism in P. effusa.