Molecular Genetic Support to Optimize the Breeding of Fanleaf Resistant Rootstocks

This report presents results of Walker lab efforts to optimize the breeding of fanleaf degeneration (fanleaf) resistant rootstocks through molecular genetic methods. These efforts are two-fold: 1) to understand and utilize O39-16?s (a Muscadinia rotundifolia based rootstock) ability to induce tolerance to fanleaf virus infection in scions; and 2) to understand and utilize resistance (XiR1) from Vitis arizonica to the dagger nematode, Xiphinema index, which vectors grapevine fanleaf virus (GFLV) from vine-to-vine by root feeding. We have genetically and physically mapped XiR1 and we have transformed two candidate genes, XiR1.1 and XiR1.2 into V. rupestris St. George, V. vinifera Thompson Seedless, and tomato (all susceptible to X. index feeding) and have produced plantlets that are approaching the size needed to transfer to the greenhouse for X. index inoculation. These studies will determine which of and if these gene candidates controls resistance to X. index. We are also working on ways to rapidly evaluate fanleaf resistance and tolerance through in vitro grafting. We are also preparing to test saps from progeny of the 101-14 x M. rotundifolia population as a means of screening for the ability to induce tolerance to fanleaf disease. We worked with the UC Davis Metabolomics Center director and Doug Adams to identify a group of 5 metabolites and several cytokinin precursors that might be involved in this response based on their levels in infected and healthy O39-16 and St. George. These compounds will be pre-screened in the rotundifolia-based population and about 10 other Vitis species x M. rotundifolia hybrids I have produced. The saps are harvested and are preparing processing at the Metabolomics Center and more will be collected this year.