Breeding Grapevine Rootstocks for Resistance to Soil-Born Pests and Diseases

The development of new rootstocks is necessary to address viticulture’s current and future soil-bome problems such as: fanleaf degeneration; nematode complexes; armillaria root rot; drought tolerance; and salinity tolerance. Phylloxera is wide spread in the state, thus all new rootstocks must have dependable phylloxera resistance. Rootstocks are also needed for horticultural characters such as control of vigor and fruit maturity. This proposal primarily addresses the needs of wine grape growers. A similar proposal is funded jointly by the California Table Grape Commission and the California Raisin Advisory Board. I have worked hard to establish a Grapevine Nursery Commission that might also be a source of funds for rootstock breeding work, and I continue to pursue funding from private sources. Because of the need for many lab and field personnel, breeding is very expensive and combined funding is essential for progress. At present the departmental vineyard crew provides me with free labor for such things as planting, training, staking, trellising and grafting. This free labor source is not likely to continue as UC and Departmental budgets worsen. Additional field and lab help will be needed as the breeding program begins field testing and determinations of fruit and wine quality. Significant progress has been made in the lab and field evaluations are set to begin. We bench-grafted selected seedlings from the 1989 populations that have propagated well, been resistant to root knot nematode and should have high levels of phylloxera resistance. Replicated field trials of these grafted seedlings (we used both Chardonnay and Flame Seedless as scions) will begin at nematode and phylloxera infested sites this summer. Next year more cuttings of these seedlings will be available to establish trials at the Oakville Station and other select sites. Some of the seedlings that Lider produced in the 70’s have also been bench-grafted with the same scions. These were selected for possible broad-based nematode resistance (including dagger and root knot) and phylloxera resistance. Mike McKenry at the Kearney Ag Center will test additional selections from the 1989 populations in late June. He will infest the seedlings with 3 very aggressive strains of root knot nematode, the effects will be assessed in November. We have made 123 crosses thus far this year, more are expected as aestivalis, berlatidieri, cinerea, rotundifolia and rufotomentosa come into flower in June. Crosses were made to produce seedlings resistant to dagger and root knot nematodes and to combine these traits with phylloxera resistance and ease of propagation. Forty seven of the crosses were made to begin study of the evolutionary relationships between the Vitis species to allow us to better understand similarities in their resistance and horticultural characters. We also have many seedlings from the 1992 crosses that should be ready for field planting late this summer. Work has also progressed in the lab. While studying phylloxera DNA we found that many A’s and B’s exist in California, suggesting that B type is not spreading, but that it is selected for at a given AXR#1 site. This means that any site with AXR#1 and phylloxera is at risk, and that preventing B types from spreading to a given location is not likely to prevent decline. These discoveries would not have been possible without financial support for a post-doc from The Wine Group. We also succeeded in putting both the dagger nematode, Xiphinema index and phylloxera into tissue culture with grape. We are in the process of testing these in vitro systems to see if they can be used to reliably screen seedlings for resistance. If in vitro pest resistance reactions differ from whole plant reactions we will not be able to use in vitro techniques to screen seedlings, but they will still be valuable for studying pest biology. We identified new and strong sources of resistance to Meloidogyne incognita (root knot nematode) in various Vitis species and these were used in crosses this spring. We completed an isozyme study that allows identification of the rootstocks grown in California, and used the same technique to study variability in Vitis cordifolia, longii and riparia. Isozyme characterization of these species will help us define their range and taxonomic identity, and help choose northern selections that may have the potential to hasten fruit maturity and be useful in rootstock breeding.

Biotechnology for Grape Improvement

The goal of this research is to produce economically significant genetic improvements in existing grape varieties by using genetic engineering techniques to either 1) add new genes that confer traits such as insect or disease resistance or that enhance specific desirable fermentation or flavor properties, or 2) modify the function of existing genes so as to reduce or eliminate specific fruit components, such as browning enzymes, ethyl carbamate precursors, or seeds. Varietal characteristics other than the ones being deliberately engineered are expected to remain unchanged. We have continued to make progress toward the development of gene transfer technology for grape. We are able to introduce new genes into grape tissues, but have not yet produced whole vines that express new genes. The most successful gene transfer method for other plant species. Agrobacterium-mediated transformation of leaf explants, from which the regeneration of transgenic adventitious shoots is subsequently induced, has not been successful with grape. In order to develop better strategies for introducing economically significant genes into existing grape varieties, the cells in leaf explants that give rise to adventitious shoots were identified by histological analysis. The cells in leaf explants that are transformed by Agrobacterium were also identified in order to determine whether transformed cells could contribute to shoot meristems. Very few transformed cells were found in regions of the leaf explant that give rise to shoots, indicating that, although this method might produce occasional transgenic plants, it is unlikely to be a means by which this could be accomplished routinely. Other strategies that have been successfully employed with other plants, including Agrobacterium-mediated transformation of proliferating somatic embryo cultures and transformation of individual somatic embryos from which adventitious shoots can be induced, are now being pursued. A study of the biochemical interaction between grape tissues and several grape-specific Agrobacterium strains that we have isolated from California vineyards is underway in order to determine whether these strains might be engineered to introduce new genes more effectively than the laboratory strains in general use.