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Resistance

Mechanism of Increased Susceptibility of Bleached Pea Seeds to Seed and Seedling Rot. R. Loria, Graduate research assistant, Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing, 48824; M. L. Lacy, professor, Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing, 48824. Phytopathology 69:573-575. Accepted for publication 5 December 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-573.

Seeds of some pea (Pisum sativum) cultivars may lose normal green color during maturation. The process, which is known as “bleaching,” is associated with increased susceptibility to seed and seedling rot. When surface-sterilized unbleached seeds were inoculated with Fusarium solani f. sp. pisi, those incubated in exudate from bleached seeds had a higher disease rating than those incubated in exudate from unbleached seeds. Disease severity was similar, however, if exudate effects were minimized by injecting conidial suspensions directly into the cotyledons of bleached and unbleached seeds. Exudates from bleached and unbleached seeds contained similar quantities of fourteen amino acids, but bleached seed exudate contained approximately three times more soluble carbohydrate (glucose, fructose, and largely sucrose) than unbleached seed exudate. The carbohydrate-containing fraction of seed exudates stimulated chlamydospores of F. solani f. sp. pisi to germinate in field soil. The neutral fraction of bleached seed exudate caused 40% of the chlamydospores to germinate but the same fraction of unbleached seed exudate promoted only 10% germination. Differential carbohydrate, but not amino acid, exudation apparently causes differences in susceptibility of bleached and unbleached seed to F. solani f. sp. pisi.