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.

Clonal Testing of Winegrapes in the San Joaquin Valley

Executive Summary: An on-going San Joaquin Valley wine cultivar clonal evaluation trial was initiated in 1986 and planted into the first trial block in 1987. Location is the University of California Kearney Agricultural Center, Parlier where cultural conditions and practices can be closely monitored. All of the selections are indexed FPMS sources, most of which are registered. None have ever been compared in clonal studies. Thus, industry would benefit from performance information on available selections. This study utilizes 15 single-vine replicates in randomized complete blocks for each cultivar. 1991 was the third year of comparison for three selections each of French Colombard and Chenin blanc. Each cultivar compares two different selections which are registered (indexed as virus free) but not heat treated. Additionally, each cultivar includes a heat treated selection. Thus, we are studying the possible influence of heat treatment on virus-free material of French Colombard and Chenin blanc. Barbera was in its first year of data taking. This compares an Italian selection, Rauscedo 6 (FPMS Clone 2), with Marshall (FPMS Clone 1). Barbera Clone 1 presently involves much of the present commercial acreage but was later found to contain mild leafroll. French Colombard. Clone 1 is the highest yielding, latest maturing, and most rot susceptible, possibly due to higher fruitfulness (cluster numbers and berries per cluster). Clone 5 tends to be the lowest yielding and earliest maturing selection over the three years of data taking. Presently, Clone 2 would appear to be the best overall selection. It is intermediate in yield and has favorable fruit composition characteristics. Interestingly, it is a heat treatment of Clone 1. Chenin blanc. Clone 5 produces the smallest berries and clusters of earliest maturity. However, yields are lowest and rot tends to be highest with this selection. Presently, Clone 4 would appear to be the best selection. It is the highest yielding and with the lowest rot incidence. This is a heat treatment of Clone 1 with more favorable vine yield characteristics. Barbera. These two selections were included to compare the widely planted Clone 1 (Marshall) with the only registered and recently introduced Clone 2 (Rauscedo 6). Because of its virus-free status, only Clone 2 should be recommended for planting at this time. However, its larger berry size and higher yields contribute to later fruit maturity and possibly lower anthocyanins per fruit weight. Further evaluation will be necessary to confirm this preliminary recommendation. Zinfandel was eliminated in 1991 due to inclusion of a misnamed selection. Grenache will be added with a comparison of three selections in 1993. Sanqiovese and Muscat blanc are also planned for future evaluation. Other cultivars will be added as promising selections become available. Wine samples will be made from French Colombard and Chenin blanc if full funding becomes available in 1992.

Evaluation of Winegrape Clones

Five clonal trials were harvested in 1991, two Chardonnay, two Cabernet Sauvignon, and 1 combination of Zinfandel, Primitivo and Sangiovese. Clones were assessed for yield components and fruit maturity indices. Small-lot wines were made from only one trial (Jaeger Chardonnay) because of a shortfall of funds. The cane-pruned Jaeger Chardonnay clonal trial yielded less on average than the cordon-spur-pruned Beringer trial, although the trends bore some similarities. As in the past, clones 4 and 5 were among the highest yielding in both trials. Clone 14 at Jaeger and clones 6, 14 and 15 at Beringer were intermediate in yield. As has been the historical case, clone 16 yielded one-half to one-third of the highest yielding clones. It is interesting that the yield-pruning ratios varied from 1.5 to 7.8 at Jaeger and from 2.8 to 13.3 at Beringer. There has been a consistent trend for heavier pruning weights for clone 6 and 15, intermediate pruning weights for clones 4, 5, and 16 and low pruning weights for clone 14. The Cabernet clonal trial at Mondavi Woodbridge is showing that the highest yielding clones are 8 and 21, with clones 2, 4, 5, and 10 as intermediate and clone 6 as the lowest. The difference between the high and intermediate yielding clones is less than in past years. For the Zinfandel-Primitivo-Sangiovese trial, the 10-vine plots were split into thinned and not-thinned groups in 1991. Thinning of course reduced yield but did not result in larger vine size at dormant pruning in 1991-2. There were few differences among the Zinfandel selections. In many respects, Primitivo yield components were very similar to Zinfandel, although the formere seemed to ripen sooner. Sangiovese clones ripened sooner than either Zinfandel or Primitivo. Sangiovese 3 had fewer berries/cluster than Sangiovese 2, althoug the berries were somewhat heavier. Over the past two to three years additional trials have been established in Napa (Merlot, Cabernet Sauvignon), Sonoma (Chardonnay, Pinot noir – sparkling), Lake (Cabernet Sauvignon, Zinfandel) and Santa Barbara (Pinot noir – red and sparkling). Discussions are underway for Napa (Merlot, a second site) and Santa Barbara (Chardonnay).