Differences in Aggressiveness of Erwinia carotovora subsp. betavasculorum Strains and Their Reactions to Sugar Beet Cultivars. E. D. Whitney, USDA-ARS, Research Plant Pathologist, 1636 East Alisal St., Salinas, CA 93905. B. E. Mackey, USDA-ARS, Consulting Statistician, 800 Buchanan St., Berkeley, CA 94710. Plant Dis. 73:220-222. Accepted for publication 17 October 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/PD-73-0220.

In tests conducted in the greenhouse, strains of Erwinia carotovora subsp. betavasculorum caused significantly different amounts of disease in sugar beet. The apparent aggressiveness of the strains varied because of a cultivar resistance × strain interaction. A large difference in cultivar resistance to individual strains was also found. In tests conducted in the field, very aggressive strains infected a higher percentage of beets than less aggressive strains (19 vs. 3.7%), increased the percentage of rot per diseased beet from 8.7 to 44.3%, and raised the disease index from 0.2 to 3.5%. Because of cultivar × strain interactions, we suggest that several of the most aggressive strains of the bacterium be used when selecting for resistance, to allow reliable identification of the most resistant plants.

Keyword(s): selection.