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Disease Note.

Root Rot of Sugar Beet Caused by Pythium deliense in the Texas Panhandle. C. M. Rush, Texas Agricultural Experiment Station, Amarillo 79106. Plant Dis. 71:469. Accepted for publication 6 February 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0469A.

Wilted sugar beets (Beta vulgaris L.), similar to those infected by Rhizoctonia solani Kuhn, were observed near Bushland, Texas, in August 1986. Black lesions covered with white mycelium were observed on excavated roots. The lesions appeared to initiate on the bald face of the root rather than on the vascular groove. The black discoloration extended well into the root. Severely infected roots were rubbery but maintained their integrity. Pythium deliense Meurs was consistently isolated from infected beets and rhizosphere soil, using potato baits, selective media (1), and direct isolation techniques. Curved oogonial stalks, diagnostic for P. deliense, were observed on water agar cultures, thereby eliminating P. aphanidermatum (Edson) Fitzp. as the pathogen. The first report of P. deliense in North America came from Arizona in 1982 (2) and was the first time the fungus was associated with a disease of sugar beet. This is the first report of P. deliense on sugar beet in Texas and only the second report of the fungus in the United States, extending the known range of the pathogen.

References: (1) S. M. Mircetich and J. M. Kraft. Mycopathol.