Breeding grapevine rootstocks for resistance to soil-borne pests and diseases
About 8,000 seeds from the 1993 crosses were planted during the winter of 1993-94. We planted 6,675 of these seedlings in the vineyard during the summer of 1994. Over half of these seedlings were from crosses designed to produce resistance to a variety of nematodes including root knot, dagger and nematode complexes; tolerance to drought and salinity; combining phylloxera resistance in all backgrounds; and appropriate levels of vigor. Fifty-four crosses were made in 1994 to address these same issues; 2326 seeds were produced from these crosses, about 1,000 are ready for planting as soon as the vineyard site is prepared. Progress with the 1989 seedlings has been slow because of repeated failures with the bench-grafting crew. These mistakes have been identified and the same series of materials is being bench-grafted again this winter. Grafting success with these seedlings has been good, however the soil mix into which they are planted after callusing, and the greenhouse culture they have been receiving, has been poor. These problems have been remedied, however they will not be completely solved until I have my own field and grafting crew. Mike McKenry, at the UC Kearney Ag Center, has completed screening the best of these seedlings for resistance to a complex nematode population consisting of his most aggressive root knot races. Three of these seedlings 8913-02 (rupestris A. de Serres X rotundifolia Trayshed), 8913-21 and 8916-02 (rupestris Wichita Refuge X rotundifolia Dixie) did well in his screen and are ready for field testing. A paper detailing a screening of Vitis species for resistance to root knot nematode has been published (Walker, Ferris and Eyre. 1994. Resistance in Vitis and Muscadinia species to Meloidogyne incognita. Plant Disease 78:1055-1058). Several interesting new sources of resistance were discovered and we are preparing to use them in crosses next year to improve rooting ability of known resistant species that root poorly. A graduate student of mine finished a manuscript (Fong, Walker, and Granett. RAPD assessment of California phylloxera diversity. Journal of Molecular Ecology, In Press), which details our discovery that phylloxera biotype definitions are groups of genotypes and not single types. This means that B type phylloxera are not spreading from a single point of origin, but are capable of evolving wherever AXR#1 is used. We have also begun a project to examine the genetic variability in dagger nematode (Xiphinema index) populations across the state. We have completed collections from San Joaquin, Sonoma, Napa, Monterey, Kem and Fresno counties. This study will examine the diversity that exists in populations of X. index, (high levels would not be expected from a predominantly parthenogenetic and imported pest) and will lead to studies on their ability to vector fanleaf virus and damage grape roots. We will then be able to utilize the most aggressive nematode populations in screening tests and be able to study differences in GFLV that may exist.