Inheritance of Tolerance to Xiphinema Index in Vitis Species

¹ Department of Viticulture and Enology University of California, Davis, California 95616.
² Division of Nematology University of California, Davis, California 95616.
³ Department of Viticulture and Enology, University of California, Davis, California 95616.

Previous work has demonstrated that there is variability among Vitis species for tolerance to the parasitic nematode, Xiphinema index. Based upon this information, crosses were made among a number of tolerant and susceptible Vitis species and cultivated varieties. The seedling progeny of each cross were evaluated for tolerance based upon visible root symptoms. On the basis of segregation patterns observed in these progeny, two tentative genetic models for X. index tolerance are considered. The simplest method involves one gene, with tolerance being dominant. In a second model, tolerance is governed by two genes, either of which can condition tolerance. In one gene, tolerance is dominant, and in the other it is recessive. Studies to further elucidate the basis of X. index tolerance are proposed, and the relevance of these findings to grape breeding programs is discussed.