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Aboveground Infection of Snap Bean by Ditylenchus destructor, the Potato Rot Nematode. A. E. MacGuidwin, Associate Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. D. J. Wixted, and B. D. Hudelson. Outreach Specialist, Department of Agronomy, and Research Specialist, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 76:1097-1102. Accepted for publication 7 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1097.

Microcosm and field studies were conducted to determine the importance of shoot infection to the population dynamics of Ditylenchus destructor associated with snap bean (cv. Amity). All parts of plants grown in microcosms, both above- and belowground, were infected with nematodes. After planting (17 wk), numbers of nematodes increased in soil, fibrous roots, and above- and belowground portions of the hypocotyl and decreased in cotyledons, epicotyls, and leaves. Population densities recovered outside roots below the soil line averaged 9.5 times greater than those recovered inside fibrous roots. Soil moisture at the time of planting and the age structure of the nematode inoculum affected the number of nematodes recovered from shoots 3 wk after planting. Inoculum consisting primarily of adults or a 1:1 mixture of adults and juveniles decreased seedling emergence 5 days after planting and resulted in higher nematode populations as compared to inoculum composed primarily of juveniles. Placement of nematode inoculum was important for shoot infection: the greatest number of nematodes was recovered from shoots of plants grown from seed in direct contact with nematodes. Of the potato tubers grown in pasteurized soil infested with stems, fibrous roots, or soil from snap bean harboring D. destructor, 100% were infected with this nematode. No nematodes were recovered from shoots of snap bean grown in field plots or sampled from a commercial field, nor were any isolated from soil, other parts of snap bean, or other hosts on the sites. D. destructor was recovered from shoots from one of 24 snap bean plants grown in mesocosms infested with nematodes 4 yr earlier. That D. destructor was recovered from all parts of plants grown under controlled conditions and increased in parts not traditionally sampled indicates that shoots should be examined when estimating population densities of this nematode.

Keyword(s): nematode sampling, Phaseolus vulgaris.