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Genetic Control of Primary Haustorial Development of Erysiphe graminis on Wheat. Mary Joy Haywood, Research assistant, Botany and Plant Pathology Department of Michigan State University, East Lansing, MI 48824, Present address of senior author: Assistant professor, Carlow College, 3333 Fifth Ave., Pittsburgh, PA 15213; Albert H. Ellingboe, professor, Botany and Plant Pathology Department of Michigan State University, East Lansing, MI 48824. Phytopathology 69:48-53. Accepted for publication 17 July 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-48.

Genes conferring resistance in wheat to Erysiphe graminis f. sp. tritici affect the ontogeny of early interactions between host and parasite. The rate of development of primary haustoria of E. graminis f. sp. tritici on five near-isogenic lines of wheat containing single genes for reactions to E. graminis (MS-1) was determined by direct microscopic observations made after fixation and staining of epidermal strips with aniline blue every 2 hr from 8 through 30 hr after inoculation. Inoculated plants were held under environmental conditions known to favor development of the parasite. With the compatible Px/pmx genotype, 87% of the parasite units formed haustoria 3555 μm long within 30 hr after inoculation. With the incompatible genotypes, Pla/Pmla, P2a/Pm2a, P3a/Pm3a, and P4a/Pm4a, the percentages of haustoria 3555 μm long by 30 hr after inoculation were 15, 66, 18, and 3, respectively. More than 75% of the host cells in the successful infections with Pla/Pmla, P2a/Pm2a, P3a/Pm3a, and P4a/Pm4a, in which the haustoria were 35 μm or more in length, were heavily stained, indicating mesophyll collapse and necrogenic protoplasts. These results provide evidence that the different genotypes affect different stages in the host/parasite interactions earlier than previously reported.

Additional keywords: host-parasite interactions, powdery mildew, primary infection, Triticum aestivum.