THE GENETICS OF AND BREEDING FOR PIERCES DISEASE RESISTANT GRAPES

• Author(s): Ramming, David; Tenscher, Alan; Walker, Andrew;
• Abstract: We continue to make many crosses, produce thousands of seeds and embryos, and about four thousand plants in the field each year. We have been increasing the number of seedlings and high fruit quality selections we test under our greenhouse screen. This screening is very severe, but material that passes the screen is reliably resistant and dramatically restricts Xylella fastidiosa movement. We are also co-screening for powdery mildew resistance. The heritability of Xf resistance from a range of resistant Southeast US (SEUS) cultivar and species parents is not consistent some parents produce few resistant offspring, while others produce a large percentage making careful parental screening very important. We have been able to expand our Xf screening this year and are currently testing 178 potential parents (selected backcross progeny, new SEUS parents, and Olmo VR hybrids) and will have resistance results before the 2004 pollination season so that crosses can be optimized. The USDA embryo rescue process has produced a large number of progeny from crosses of resistant males to seedless females including 265 plants from second generation backcrosses. Culture efforts this year (2,702 ovules) produced 484 embryos that are now germinating. Crosses continue to be made with SEUS resistant wine grape selections to vinifera wine grapes including Merlot, Syrah, and Olmo selections. Rootstock crosses are also being made and seedlings evaluated and will be used in joint efforts to examine possible inducible tolerance to PD via rootstocks.
• Publication Date: Aug 2003
• Journal: 2003 Pierce's Disease Research Symposium