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Postharvest Pathology and Mycotoxins

The Effect of Seed Infected with Phoma betae on Rot and Sucrose Yield of Stored Sugar Beet. W. M. Bugbee, Plant pathologist and plant physiologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, North Dakota State University, Fargo 58105; D. F. Cole, adjunct professors, Department of Plant Pathology and Agronomy, North Dakota State University, Fargo 58105. Phytopathology 71:357-359. Accepted for publication 30 August 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-357.

Sugar beet seeds of cultivar US H20 infected with Phoma betae were treated with recommended amounts of fenaminosulf, a mixture of pentachloro-nitrobenzene and 5-ethoxy-3-(trichloromethyl)-1, 2, 4-thiadiazole, prochloraz, or thiram. Stand counts for any of the seed treatments were not improved over nontreated seed under field conditions in 1977 and 1978. The thiram-soak treatment in 1977, and all treatments in 1978, reduced Phoma betae infection in surviving seedlings. The most effective treatments were thiram soaking, and prochloraz. All seed treatments in 1978 resulted in less rot in roots stored for 150 days at 46 C compared with storage rot in roots from nontreated seed. Storage rot was positively correlated with numbers of surviving seedlings infected with P. betae. Regression analysis showed a 0.04% increase in storage rot for each 1% increase in infected seedlings. The correlation coefficient was significant (P = 0.05) but low (r = 0.15), indicating that sources of P. betae inoculum other than the seed were contributing toward infection and rot. Therefore, seed treatments to reduce infection by P. betae would result only in partial reduction of storage rot, insufficient to increase recoverable white sugar per ton of beets.