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Leaf Sheath Blights of Sorghum bicolor Caused by Sclerotium rolfsii and Gloeocercospora sorghi in South Texas. G. N. Odvody, Assistant professor, Texas A&M Research and Extension Center, Route 2, Box 589, Corpus Christi 78410; D. B. Madden, research associate, Texas A&M Research and Extension Center, Route 2, Box 589, Corpus Christi 78410. Phytopathology 74:264-268. Accepted for publication 8 September 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-264.

Sclerotium rolfsii (causal agent of southern sclerotial rot) and Gloeocercospora sorghi (causal agent of zonate leaf spot) caused leaf sheath blights on grain sorghum (Sorghum bicolor) in fields and nurseries in South Texas. S. rolfsii infected and killed one to all leaf sheaths of susceptible sorghums growing in saturated soil under hot, humid conditions. Sclerotia of S. rolfsii were often present on the outside of necrotic leaf sheaths. G. sorghi also infected basal and underlying leaf sheaths on susceptible cultivars under hot, humid conditions. Sclerotia were produced in large quantities and gave a gray appearance. Infection of sheaths by G. sorghi either preceded or occurred simultaneously with infection of leaf blades. Free and residue-associated sclerotia of G. sorghi were isolated from field soil and germinated readily in culture. Three field soils had 4- 17 germinable sclerotia per gram of air-dry soil. Occurrence of southern sclerotial rot was sporadic and predominantly in poorly drained areas, but zonate leaf spot on sheaths was present in most fields. Neither disease was economically important, but some cultivars were extremely susceptible to either one or both diseases in the field.