Presence on Sweetpotato Through the Growing Season of Erwinia chrysanthemi, Cause of Stem and Root Rot. V. Duarte, Former Graduate Student, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, LSU Agricultural Center, Baton Rouge 70803-1720. C. A. Clark, Professor, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, LSU Agricultural Center, Baton Rouge 70803-1720. Plant Dis. 76:67-71. Accepted for publication 2 August 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0067.

Storage roots of sweetpotato (Ipomoea batatas) cv. Beauregard were either dipped in a 10⁸ cfu/ml suspension of a rifampicin-resistant, virulent strain of Erwinia chrysanthemi (2rr) or implanted with a micropipette tip containing 50 ?l of the same suspension. The roots were then planted in field beds. At both the first and second harvests of plants, slips (sprouts) were cut above the soil line or pulled from the mother roots and transplanted to the field. Strain 2rr was recovered from inoculated roots 7 days after the roots were bedded and at the first and second harvests of slips. The bacterium also was present on or in symptomless vine cuttings at transplanting and on or in the underground stem and daughter storage roots at harvest. However, little stem rot was observed in the field. Inoculation of stem cuttings at transplanting or whether pulled or cut slips were used for transplants did not affect disease occurrence. Strain 2rr was recovered from 23 and 9% of samples from pulled and cut slips at harvest, respectively. When slips of sweetpotato cv. Jewel were cut with a contaminated knife, strain 2rr was recovered from the cut stub of the sprout, from slips removed at the subsequent cutting, from the surface of the mother root, and from the underground stem of the daughter plants at harvest. Thus, symptomless mother roots, slips, and vines may harbor latent populations of E. chrysanthemi that may serve as sources of inoculum for bacterial stem and root rot of sweetpotato.