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Etiology

Pythium Species Pathogenic to Onion Seedlings Grown on Organic Soils in New York. W. L. Bruckart, Graduate research assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853; J. W. Lorbeer, professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853. Phytopathology 72:469-475. Accepted for publication 9 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-469.

Pythium irregulare and P. coloratum isolated from onion seeds and seedlings grown in natural organic (muck) soils in New York were strongly pathogenic to onion seedlings. Five of six other species (P. ultimum, P. sylvaticum, P. torulosum, P. paroecandrum, and P. rostratum) from the same sources were weakly pathogenic and isolated infrequently. P. irregulare caused significantly more damping-off than did P. coloratum and was isolated from organic soils cropped to both onion and lettuce. P. coloratum was associated most frequently with one soil having a history of lettuce culture.