Dr. Walker's lab works on combating grapevine pest and disease problems by breeding resistant rootstocks and fruiting varieties. They study the genetic diversity of grape species and varieties and how these species resist pests and diseases. They also study the genetics of these resistances and use the results to create genetic maps with markers that are tightly linked to resistance genes and can be used to make screening for resistance more rapid and precise. Armed with these genetic tools and aggressive vine training techniques, the Walker lab has reduced the seed-to-seed cycle to two years, greatly accelerating their grape breeding efforts. 

The best example of their use of these techniques is in the development of Pierce's disease (PD) resistant winegrapes. This bacterial disease is caused by Xylella fastidiosa, which is vectored from a wide-range of host plants by sharpshooter insects. The disease clogs water-carrying xylem vessels leading to vine death in 2 to 4 years. The Walker lab discovered a source of resistance in a grape species called Vitis arizonica, which grows from the southwestern US to northern Mexico. This species has a single dominant gene for resistance. They have used marker-assisted selection to integrate the resistance from V. arizonica while improving the wine quality of the hybrid offspring in each generation. They now have advanced selections that are 97% V. vinifera (the European wine grape) with strong resistance to PD from V. arizonica, and excellent fruit and wine quality. These plants are in the process of being multiplied at grape nurseries prior to their release. The next step is one of the more difficult ones -- naming and marketing these new winegrapes! Even though marketing new wine varieties is difficult, growers and winemakers from Healdsburg to Virginia are excited at the prospect of using classically bred winegrape varieties with strong resistance to PD and excellent vinifera-like wine quality. Next up, using these same tools to combine PD resistance with powdery mildew resistance!