1a. Objectives (from AD-416):
Develop Pierce's disease (PD) resistant table and raisin grape germplasm/cultivars with fruit quality equivalent to present day standards. Develop molecular map and markers for Xf/PD resistance based on resistance from BD5-117 selection from southeastern United States.
1b. Approach (from AD-416):
1) Backcross the most advanced resistant hybrids (V. arizonica and BD5-117 sources of resistance) to high quality V. vinifera seedless table and raisin grapes. 2) Use embryo rescue to facilitate the hybridization of seedless parents. 3) Use molecular markers to select resistant V. arizonica backcross seedlings. 4) Select seedlings with highest fruit quality in the field and verify resistance by greenhouse inoculation. 5) Field test best resistant selections for PD resistance under natural and inoculated conditions. 6) Establish production and quality trials of selections with commercial potential. 7) Develop molecular map of BD5-117 family to locate PD resistant QTL and associated molecular markers. Documents reimbursable agreement with the University of California Pierce’s Disease Research Grants Program.
3. Progress Report:
The agreement was established in support of Objective 4B of the in-house project to develop advanced selections of table grapes and raisins bearing Pierce's disease (PD) resistance, high quality fruit, and desirable viticultural characteristics. This research contributes to development and evaluation of grape seedling populations and advanced selections to improve table and raisin grape germplasm with resistance to PD. PD-resistant table and raisin grape varieties are needed to overcome increased incidence of PD as a result of introduction of the glassy-winged sharpshooter. Fruit quality of resistant varieties needs to be equivalent to varieties currently grown commercially. Production of additional backcross (BC) generations to combine high quality table and raisin grapes with PD resistance is continuing. This year’s selection of six BC4 table, 8 BC4 and 3 BC3 raisin grape selections show increased fruit qualities. They were propagated into first stage production trials. Three table and seven raisin selections show enough promise for inclusion in second stage cultural production trials. Eleven crosses to combine PD resistance with high quality table and raisin grapes were made. The crosses consisted of 44,187 emasculations. In addition, 15 crosses to combine powdery mildew (PM) and PD resistance were made, consisting of 47,347 emasculations. Marker assisted selection was used to screen 1,265 seedlings of which 505 carried the marker for resistance. PD resistance of over 38 parents and selections from V. arizonica populations has been tested in greenhouse tests to insure the molecular markers for PD resistance continue to function. Two hundred and forty-three seedlings of the BD5-117 mapping family, with PD resistance different than V. arizonica, have been greenhouse tested. A preliminary molecular map based on 70 SSR primers and 144 seedlings indicate a major QTL for PD resistance on linkage group 2. This means selected molecular markers from linkage group 2 might be useful to select resistance from the BD5-117 source of resistance. This collaborative research between USDA/ARS, Parlier and University of California, Davis has the unique opportunity to develop high quality PD resistant table and raisin grape cultivars for the California grape industry.