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Improved Methodology for Evaluating Resistance in Sweet Potato to Streptomyces ipomoea. J. W. Moyer, Department of Plant Pathology, North Carolina State University, Raleigh 27650; C. L. Campbell(2), E. Echandi(3), and W. W. Collins(4). (2)(3)Department of Plant Pathology, North Carolina State University, Raleigh 27650; (4)Department of Horticultural Science, North Carolina State University, Raleigh 27650. Phytopathology 74:494-497. Accepted for publication 30 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-494.

A method was developed for evaluating resistance in sweet potato to Streptomyces ipomoea. Resistance in 15 sweet potato clones was evaluated under field, greenhouse, and laboratory conditions. Before transplanting was done, field plots were artificially infested with an enriched sand medium colonized with S. ipomoea. Greenhouse trials were conducted in 15-cm clay pots containing infested sand diluted with autoclaved sand to provide an inoculum concentration of 104- 106 propagules per cubic centimeter of sand. Fleshy root slices were assayed directly on the infested sand at the same inoculum concentration. There was a negative correlation (P <0.05) between disease development on fibrous roots in the greenhouse and production of fleshy roots in the field. Disease development on fleshy root slices was significantly (negatively) correlated (P <0.05) with both production of fleshy roots and percentage of marketable fleshy roots produced in the field.