Host Range and Influence of Nutrition, Temperature, and pH on Growth of Pythium violae from Carrot. J. K. SCHRANDT, Graduate Student, Department of Plant Pathology, University of California Davis 95616. R. M. DAVIS, Extension Specialist, and J. J. NUNEZ, Staff Research Associate, Department of Plant Pathology, University of California Davis 95616. Plant Dis. 78:335-338. Accepted for publication 30 December 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0335.

The host range of Pythium violae, the cause of cavity spot of carrots, was determined in artificially infested potting mix in the greenhouse and in naturally infested field soil. Six new symptomless hosts were identified in greenhouse pathogenicity tests: cowpea, broccoli, celery, cucumber, sugar beet, and watermelon. Cowpea and cauliflower were also infected in natural field soil. The susceptibility of three previously reported hosts of P. violae, carrot, alfalfa, and wheat, was confirmed. The utilization of 10 carbon sources, 13 nitrogen sources, and three vitamins by P. violae was examined in liquid culture under controlled conditions. Although some growth was observed on all carbon and nitrogen sources tested, optimum growth of P. violae occurred when fructose, sucrose, or glucose was the sole source of carbon and when arginine, serine, or glutamine was the sole source of nitrogen. P. violae also utilized certain polysaccharides and oils, e.g., potato starch and wheat germ oil, and did not require an exogenous source of vitamins. The optimum temperature range for growth was 16-22°C, and the optimum pH range was 5.5-8.0.