Field Pathogenicity Studies of Four Species of Plant-Pathogenic Nematodes on French-American Hybrid Grapevine Cultivars in Michigan. D. C. Ramsdell, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. G. W. Bird, F. W. Warner, J. F. Davenport, C. J. Diamond, Department of Entomology, and J. M. Gillett, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Plant Dis 80:334. Accepted for publication 15 December 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0334.

Ten French-American hybrid grapevine cultivars were evaluated for their reactions to four plant-parasitic nematodes: Criconemella xenoplax, Meloidogyne hapla, Pratylenchus pene-trans, and Xiphinema americanum. In the spring of 1987, following soil fumigation, own-rooted vines of the cultivars Couderc 1202, Couderc 1616, Couderc 3309, Kober 5BB, Teleki 5A, Teleki 5C, Foch, Seyval, Vidal, and Vignoles were planted into microplots arranged in a completely randomized design with five replications per treatment. The microplots were inoculated with 2,500 M. hapla eggs, 2,500 juveniles and adults of the other three nematode species, or not inoculated. In 1989 and 1990, cane length was measured for each vine, and from 1991 to 1993, vine pruning weights and fruit yields were recorded. The experiment was terminated in the fall of 1993. At least one of the four species of nematodes reduced growth or yield of all the grapevine cultivars tested during 1 year of the study except for Couderc 1202. Yields of cv. Seyval were increased in the presence of all four species of nematodes in at least 1 year of the study, although vine pruning weight was reduced by M. hapla in 1993. In general, M. hapla was the most virulent of the nematodes studied. Meloidogyne hapla reduced fruit yields at least 1 year compared with the control plots in five of the seven cultivars from which yields were collected. Criconemella xenoplax only reduced yields of Foch, P. penetrans did not reduce yields of any cultivar, and X. americanum reduced yields of Vidal and Vignoles. This study should provide viticulturists with valuable information on nematode-grapevine cultivar interactions for management purposes