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Resistance

Evaluating Peas for Resistance to Damping-off and Root Rot Caused by Pythium ultimum. S. H. Ohh, Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108; T. H. King(2), and Thor Kommedahl(3). (2)(3)Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108. Phytopathology 68:1644-1649. Accepted for publication 8 June 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1644.

Six pea breeding lines developed at Minnesota proved to be resistant to damping-off and root rot caused by Pythium ultimum whereas two commercial cultivars were susceptible. Evaluating resistance by soaking seeds in hyphal suspensions before planting them was as effective as, and more rapid than, planting seeds in infested soil. The resistance of genotypes to damping-off was not lost by increasing exposure time of seeds in inoculum from 6 to 24 hr, by increasing inoculum concentration, or by testing in autoclaved or nonautoclaved sand or soil, but it was lost by injury to seed coats; however, each of these treatments accentuated the susceptibility of susceptible lines or cultivars. In a pea-field disease nursery, the percentage survival of plants of the nine breeding lines was greater than that of cultivar New Era, and the yield of six lines was significantly greater than that from either cultivar Alaska or New Era.