Resistance of Sweet Potato to Bacterial Root and Stem Rot Caused by Erwinia chrysanthemi. C. A. Clark, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803-1720. J. A. Wilder-Ayers, and V. Duarte. Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803-1720. Plant Dis. 73:984-987. Accepted for publication 19 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0984.

Greatest differences in resistance of sweet potato (Ipomoea batatas) storage roots to bacterial root rot were observed 6 or more days after a micropipette tip containing 50 µl of a 10⁹ cfu/ml suspension of Erwinia chrysanthemi had been inserted 1 cm into the root. The frequency of disease was variable when the suspension contained less than 10⁶ cfu/ml, but lesion size was consistent for each genotype at 10⁷–10⁹ cfu/ml. Differences among genotypes were related to the duration of active decay, whereas differences within genotypes were associated with location of the crop. Reaction among storage roots was not correlated with reaction of vines. Older “heirloom” cultivars were relatively resistant to root rot. Thus, susceptibility to bacterial root rot may have been introduced into breeding programs recently.