BREEDING TABLE AND RAISIN GRAPES WITH INCREASED FRUIT QUALITY WHILE RETAINING PIERCE'S DISEASE RESISTANCE

Abstract

The spread of Pierce's disease (PD) has greatly increased with the introduction of the glassy-winged sharpshooter into California. A collaborative breeding program to develop table and raisin grape cultivars resistant to PD was started in 2000. V. arizonica/candicans grape hybrids with PD resistance were hybridized with table and raisin grapes and the first generation screened in the greenhouse to determine resistance. The second generation was screened by molecular markers to identify resistant individuals. There was no difference between the first generation resistant and susceptible populations of D8909-15 x table grape for cluster weight, berry weight, and seed/trace weight. The cluster weight and berry size of the best resistant individuals were twice the size of the resistant parent. Aborted seeds, similar in size to the seedless parent, were also achieved in a resistant seedling. There was also no difference between first generation resistant and susceptible populations of F8909-08 x table grape selections for cluster size, berry size, and seed size. Resistant individuals with the largest berry size averaged 1.82 g compared to 3.6 to 14.4 g for the table grape parents. There was no difference between resistant and susceptible populations for berry size and seed/trace size in the second generation that resulted from backcrossing to table and raisin grapes. The mean berry size was 0.6 g larger and the mean seed/trace size decreased from 106 to 47 mg in the second generation. The second generation resistant individual with the largest berry averaged 4.9 g. Resistant individuals with undetectable seed traces, smaller than the seedless parents, were obtained in the second generation. This shows that fruit quality can be rapidly improved in the development of PD resistant grapes when efficient screening methods are used.