Interactions Between Phymatotrichum omnivorum and Sorghum bicolor. C. M. Rush, Research Scientist, Texas Agricultural Experiment Station, Blackland Research Center, P.O. Box 748, Temple, TX 76503. T. J. Gerik, Assistant Professor, Texas Agricultural Experiment Station, Blackland Research Center, P.O. Box 748, Temple, TX 76503, and S. D. Lyda, Professor, Department of Plant Pathology, Texas A&M University, College Station 77843. Plant Dis. 68:500-501. Accepted for publication 14 December 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-500.

Borescopic observations of sorghum roots grown in association with Phymatotrichum omnivorum revealed that the fungus causes small burgundy-colored lesions on the roots. After contact, however, the fungus does not continue to grow on the lesion as on cotton roots, and new strands do not develop from the point of root contact. Lesion development on sorghum roots resembles a hypersensitive resistance reaction. Sorghum plants grown in association with P. omnivorum showed no reduction in root or shoot weights compared with plants grown in the absence of the fungus. Sorghum plants were capable of supporting sclerotia formation. The number of sclerotia produced in association with grain sorghum was about half the number produced when cotton was host. It is suggested that sclerotial formation in association with grain sorghum may be a result of saprophytic survival of the fungus on root exudates as opposed to a parasitic interaction.