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Disease Detection and Losses

Time and Site of Infection of Resistant and Susceptible Germinating Pea Seeds by Pythium ultimum. T. E. Stasz, Graduate research assistant, Department of Seed and Vegetable Sciences, New York State Agricultural Experiment Station, Geneva 14456; G. E. Harman(2), and G. A. Marx(3). (2)(3)Associate professor, and professor, respectively, Department of Seed and Vegetable Sciences, New York State Agricultural Experiment Station, Geneva 14456. Phytopathology 70:730-733. Accepted for publication 21 January 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-730.

Pea seeds with seed coats colored by anthocyanins were resistant to Pythium ultimum seed and seedling diseases, whereas seeds with uncolored seed coats were susceptible. Aqueous extracts of colored seed coats inhibited P. ultimum hyphal growth in vitro, but uncolored seed coats contained no fungistatic compounds. Nicking colored seed coats greatly reduced resistance and removing them reduced it still further. After planting, fewer hyphae developed on the surfaces of colored seeds than on uncolored seeds. Hyphae also were found on unimbibed seeds. Colored seed coats were not penetrated by hyphae 100 hr after seeds were planted, whereas uncolored seed coats were penetrated within 40 hr after which hyphal growth was profuse on inner seed coat tissues. Susceptibility of seeds without seed coats (ie, embryos) varied among lines independently of seed coat color and decreased dramatically during germination In some lines this decrease occurred within 16–27 hr after planting which was before the radicles had emerged through the seed coats and before the fungus could penetrate even uncolored seed coats. In other lines, embryos remained susceptible longer. Decreased susceptibility was due not only to fewer infections, but also to less severe disease symptoms developed following infection. Hyphal growth in and maceration of host tissue were confined to discrete lesions after susceptibility decreased.