Etiology of a Root Rot Disease of Sugar Beet in Texas. R. D. Martyn, Associate Professor, Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843. C. M. Rush, C. L. Biles, and E. H. Baker. Associate Professor, Texas Agriculture Experiment Station, Texas Agriculture Research and Education Center, Bushland 79012; Graduate Research Assistant, Department of Plant Pathology and Microbiology, Texas A&M University; and Research Associate, Texas Agriculture Experiment Station, Texas Agriculture Research and Education Center, Bushland 79012. Plant Dis. 73:879-884. Accepted for publication 22 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0879.

A disease of sugar beet (Beta vulgaris) in Texas characterized by wilt and root rot has been shown to be caused by Fusarium oxysporum. The disease is similar to Fusarium yellows, caused by F. o. f. sp. betae, but is distinct in that a severe root rot also occurs that is not associated with Fusarium yellows. Scanning electron microscopy revealed that the pathogen inhabited the xylem, typical of Fusarium yellows. However, electrophoretic data on three enzymes (cinnamyl alcohol dehydrogenase, esterase, and glucose-6-phosphate dehydrogenase) revealed significant differences in isozymes produced between the Texas isolates of F. oxysporum and known isolates of F. o. f. sp. betae. The Texas sugar beet isolate may be a new forma specialis (or a new race of F. o. betae). However, further comparisons with additional isolates are necessary before a definite conclusion can be made.