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United States Department of Agriculture

Agricultural Research Service

Research Project: Improvement of Prunus and Vitis Scions for Fruit Quality and Pest Resistance

Location: Crop Diseases, Pests and Genetics Research

2009 Annual Report

1a. Objectives (from AD-416)
Develop and introduce new high quality and disease-resistant cultivars of almonds, grapes and stone fruits that will sustain American agriculture and supply high quality, nutritious fruits and almonds to U.S. consumers and international markets. 1. Continue evaluation of existing high-quality scion selections of stone fruit (apricots, nectarines, peaches, and plums) from the breeding program to identify those having desirable traits such as enhanced sugar content, novel peento flat shape and expanded ripening season, and table and raisin grapes with large seedless fresh fruit that stores and ships well, natural ‘dried on the vine’ raisin trait, economic production levels with spur pruning, and enhanced anthocyanin content for fresh and processing markets. 2. Identify Vitis accessions resistant to powdery mildew and evaluate existing table grape and raisin breeding populations and selections for high fruit quality with host-plant disease resistance. 3. Evaluate existing self-compatible almond accessions adapted to California.

1b. Approach (from AD-416)
Classical breeding techniques have been used to create segregating populations where the expression of quantitative traits has been concentrated and newly available characters have been transferred into adapted Prunus and Vitis germplasm. Plant materials in existing segregating populations of Prunus and Vitis will be selected and propagated for new cultivar development. Greenhouse and field screening will proceed to select Vitis seedlings with resistant to powdery mildew. The genetic control of raisins that dry on the vine and red flesh color in grapes will be determined through the evaluation of appropriate segregating progenies. Apricots will be selected for white flesh, for drying ability and for late maturity season from numerous segregating progenies. New self-compatible almonds will be selected having kernel qualities similar to Nonpareil, and four high kernel quality self-compatible almond selections will be trialed in isolated orchard conditions to evaluate the yield potential of self-compatible almonds in the absence of bee pollination. Formerly 5302-21220-004-00D (7/08).

3. Progress Report
A total of 35 plum, 135 nectarine and 92 peach selections were evaluated. One nectarine and 13 peaches with flat shaped fruit, and 6 peach, 19 nectarine and 5 plum selections with round fruit were promising enough for larger tests. A late freeze in early March eliminated young fruit on early flowering apricots. However, the event provided a chance to identify those selections that successfully set a crop in a late-frost year. Apricot seedlings from FY08 were field transplanted in April. Apricot fruit evaluations began the second week of May and continued through the first week of July. Six new selections were evaluated, along with 37 other existing apricot selections. Ripening curves for Brix and juice acidity were developed for a mid-season white flesh apricot. A total of 122 almond selections (91 self-compatible, 31 self-incompatible) were evaluated for important shell and kernel characteristics. Included among the evaluations were commercial standards Nonpareil, Padre, Carmel (self-incompatible) and self-compatible (SC) Tuono. Eight SC selections were shown for Almond Board of California Research and Nutrition committees during November. During the 2009 bloom, 68 seedling almonds were bagged to determine their ability to set fruit without bee visitation. Among the 68 bagged trees, 28 trees were found to be SC. For a second year, stratification and soaking treatments were imposed on seedlots from three male-sterile peach-almond hybrids to evaluate possible improvements in seedling emergence. A total of 99 seedless x seedless grape crosses were made consisting of 235,729 emasculations. One hundred sixty-nine table grape seedlings fruiting for the first time were selected and evaluated in the laboratory along with 200 existing selections. Fifteen seedless grape selections (9 red, 2 black and 4 white) were propagated in a 25 vine advanced test plot. One mid-season red, one early white, and one early black seedless selection show commercial promise. Ninety-seven raisin grape seedlings fruiting for the first time were selected for laboratory evaluation, as well as another 103 raisin selections with natural dry-on-the-vine (DOV) potential. From these evaluations, 15 new raisin selections were propagated into the natural DOV advanced test plots. Thirty-one of 101 advanced DOV selections that fruited the first time had good raisin quality and natural drying ability. Modified backcrosses were continued to combine high fruit quality from table and raisin selections with the best powdery mildew resistant selections. Twenty-seven table and raisin grape families were screened in the greenhouse and 420 resistant seedlings planted in the field. Ten new table grape selections resistant to powdery mildew with small aborted seeds had good fruit quality and natural berry size and some exceeded 5 g. Four raisin selections resistant to powdery mildew with aborted seeds smaller than Fiesta raisin were propagated into production trials.

4. Accomplishments
1. Grape Breeding Enhances Phenolic and Antioxidant Levels in Grapes Berries While Still Maintaining Quality. Many white table grape cultivars develop brown spots as a result of phenolic oxidation from bruising and rubbing, making them unacceptable for commercial markets. Less browning due to low phenolic levels and higher antioxidant levels would increase consumer and commercial acceptance of grapes. Twenty-seven table grape selections were tested by ARS scientists in Parlier, CA, for susceptibility to browning, phenolic levels and antioxidant activity. There were no significant correlations between browning and the phenolic levels or antioxidant activity in the skin or flesh. Nevertheless, the findings show that breeding advancements are being made in the development of berries with low phenolic or high antioxidant activity.

2. Fresh Market Apricot Robada is Ready for Plum Pox Virus in California. While not yet in California, plum pox virus (PPV) has been identified in North America, and has been a devastating tree disease affecting apricots in many growing regions around the world. If PPV arrives in California, many apricot varieties would be susceptible, and growers would be economically impacted with unproductive trees/orchards of affected varieties. Studies conducted by ARS scientists at Parlier, CA, throughout the last decade have revealed that Robada apricot resists attack by PPV. This information is currently valuable to California apricot growers, should they choose to establish new apricot plantings. New Robada orchards will resist this devastating disease and provide insurance to growers should PPV emerge in the California growing regions.

3. New USDA Raisin Cultivars Dry Quicker, Making Them More Suitable to More Efficient Cultural Procedures. Traditional hand harvest and drying fruit on trays is expensive and subject to damage by early fall rains, while cutting canes to dry raisins on the trellis requires special trellises and trained pruners. Slower drying raisins like Thompson Seedless may not dry completely and require supplemental drying, adding to expense and energy consumption. Six raisin cultivars were evaluated by ARS scientists in Parlier, CA, for their drying rates in three consecutive seasons. Summer Muscat, Diamond Muscat, and Primus dried the fastest while Thompson Seedless consistently dried the slowest. Grower's use of the new ARS developed raisin grapes will lead to a reduction in energy consumption for supplemental drying of weather damaged raisins.

Review Publications
Ledbetter, C.A. 2009. Using Central Asian germplasm to Improve Fruit Quality and Enhance Diversity in California Adapted Apricots. Acta Horticulturae. 814:77-80.

Karayiannis,, I., Ledbetter, C.A. 2009. Susceptibility of certain apricot and plumcot cultivars to plum pox virus infection. Acta Horticulturae. (ISHS)825:153-156.

Christensen, L., Fidelibus, M.W., Katayama, D.G., Ramming, D.W. 2008. Early-ripening grapevine cultivars for dry-on-vine (DOV) raisins on an open-gable trellis. HortTechnology:18(4):740-745.

Ramming, D.W. 2009. Water Loss from Fresh Berries of Raisin Cultivars under Controlled Drying Conditions. American Journal of Enology and Viticulture. 60:2:208-214.

Last Modified: 08/19/2017
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