Using Marker-Assisted Selection to Breed Pierce's Disease-Resistant Grapes
Pierce's disease (PD), caused by the bacterium Xylella fastidiosa, is ail important disease of grapevines in California, across the southern United States, and into South America. In regions where disease pressure is high, the Cultivation of Vitis vinifera cultivars is difficult or impossible. This study reports on the introgression of PD resistance into elite wine, table, and raisin grape genetic backgrounds and on the reliability of PCR-based marker-assisted selection (MAS) to accelerate the breeding of PD-resistant grapes. This work documents the introgression of PD resistance from a homozygous resistant form of V. arizonica, b43-17. A total of 4,321 seedlings from 83 different crosses of resistant selections and high-quality V. vinifera cultivars from the F1 and first and second modified backcross generations (rnBC1 and mBC2) were screened with two to three flanking microsatellite markers (VVIP26, ctg1026876 and VMC2a5) in the early spring 2006 and 2007. The alleles linked to resistance were unique in size and were not shared by susceptible V vinifera selections. Based on the presence of unique resistant alleles, 1,683 seedlings from wine, table, and raisin grape background were selected. The distinctiveness of these resistant alleles allows the use of MAS to optimize the breeding of PD-resistant grape cultivars.