1a. Objectives (from AD-416)
Develop Pierce’s disease (PD) resistant table and raisin grape germplasm/cultivars with fruit quality equivalent to standards of present day cultivars. Develop molecular markers for Xf/PD resistance in a family from southeastern United States (SEUS).
1b. Approach (from AD-416)
1) Backcross BC1, BC2, BC3 hybrids (F8909-08 V. arizonica source of resistance) that have been selected for Pierce’s Disease (PD) resistance to high quality V. vinifera seedless table and raisin grapes. 2) Backcross F1 and BC1 resistant bunch grapes from native SEUS source of PD resistance as identified by greenhouse tests with high quality V. vinifera seedless table and raisin grapes. 3) Use embryo rescue to facilitate the hybridization of seedless parents. 4) Use molecular markers to select resistant F8909-08 backcross seedlings. 5) Select seedlings with highest fruit quality and test in the greenhouse to determine resistance. 6) Field test best resistant selections for PD resistance under natural conditions. 7) Perform production and quality trials of selections that have commercial potential. 8) Develop rough framework map of V. vinifera table grape X BD5-117 family to locate PD resistant QTL and develop molecular markers for marker assisted selection.
3. Progress Report
The agreement was established in support of Objective 3A of the in-house project to develop Vitis (table and raisin grape) scion germplasm with resistance to Xylella fastidiosa infection and/or disease development. This research contributes to development and evaluation of grape seedling populations and advanced selections to improve table and raisin grape germplasm with resistance to Pierce’s disease (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 for commercial acceptance. Additional backcross generations to combine high quality table and raisin grapes with PD resistance is continuing. This year the first backcross 5 (BC5) crosses using V. arizonica resistance (98.5% V. vinifera) were made. An example of increased fruit quality is this year’s selection of three natural dry-on-the-vine (DOV) and seven tray dry raisin selections, and four table grape selections made from BC3 V. arizonica x V. vinifera families. They were propagated into first stage production trials. Thirty-two seedless x seedless crosses to develop BC3, BC4 and BC5 V. arizonica x V. vinifera families were made. The crosses consisted of 61,244 emasculations. Powdery mildew resistance was combined with PD resistance in 20 additional crosses of 40,025 emasculations. Two table and five raisin grapes were selected from 31 resistant plants and propagated in first stage production trials. Molecular markers were used to detect PD-resistant individuals at the young seedling stage in test tubes. PD resistance of over 185 parents and selections has been verified in greenhouse tests to insure resistance continues to co-segregate with markers. Two hundred and seven seedlings of the BD5-117 mapping family, with PD resistance different than V. arizonica, have been greenhouse tested. A rough molecular map is being developed based on 70 simple sequence primers (SSR) primers and 155 seedlings to develop additional molecular markers for PD resistance.