VIEW ARTICLE

Etiology

Pathogenicity of Three Species of Pythium to Seedlings and Mature Plants of Grain Sorghum. R. G. Pratt, Assistant professor, Texas Agricultural Experiment Station, Texas A&M University Agricultural Research and Extension Center, P.O. Box 10607, Corpus Christi 78410, Present address of senior author: Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Department of Plant Pathology and Weed Science, Mississippi State University, P.O. Drawer PG, Mississippi State 39762; G. D. Janke, research associate, Texas Agricultural Experiment Station, Texas A&M University Agricultural Research and Extension Center, P.O. Box 10607, Corpus Christi 78410. Phytopathology 70:766-771. Accepted for publication 5 February 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-766.

Pythium graminicola, P. myriotylum, and P. periplocum were isolated from mature plants of grain sorghum in Texas with symptoms of root rot and lodging. Morphological characteristics of P. graminicola isolates are described and taxonomic concepts are evaluated. Pathogenicity of the three Pythium spp. to sorghum was evaluated by inoculating inbred plants at five stages of growth. P. graminicola and P. myriotylum caused pre- and postemergence damping-off whereas P. periplocum caused no damping-off. P. graminicola greatly reduced sizes of root systems of plants inoculated at 2, 4, and 8 wk of age, whereas P. myriotylum and P. periplocum caused little or no damage. P. graminicola caused severe necrosis of roots of mature plants whereas P. myriotylum and P. periplocum caused little necrosis. Four sorghum hybrids differed in susceptibility to P. graminicola at maturity, but not at 2 wk of age. Susceptibility was not correlated with resistance to greenbug (Schizaphis graminum). Stalk rot occurred in some plants of all hybrids inoculated in the stalks with P. graminicola.