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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

2011 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
Seven apricot selections were evaluated to determine self-(in) compatibility status, and two new California-Hunza hybrids were identified as self-compatible. A rootstock trial was established with two seed-propagated peach x almond hybrids and the commercial rootstock Nemaguard using two apricot and one plumcot scion selections. Robust sampling was performed on fruit from an advanced white fleshed apricot selection to examine sugar and acid levels throughout fruit maturity. Color degradation during storage was compared in an advanced late season drying apricot to both Patterson and Goldensweet cultivars. An apricot variety trial in a low-chill environment was maintained for a second year of growth in Riverside, CA. Eleven flat peach and nectarine selections were sent to National Research Support Project 5, Washington State Univ., Prosser, WA for virus indexing. Over 2400 table grape seedlings were evaluated overall, with 237 advanced seedless selections being evaluated in the field and laboratory. Eight table grape selections were promising and added to the 27 vine test plot. Forty-one advanced dried-on-the-vine (DOV) raisin selections fruited and seventeen were dry and harvested by the third week of October. The best DOV selection, averaged 4.49 tons/acre with 13.7% moisture and a raisin grade of 77.6% B or better. The Backcross1 family for red flesh was analyzed for flesh color and anthocyanin content of flesh and skin. Five seedless raisin selections with red flesh were selected for propagation to determine production levels and raisin quality. The 238 table grape and 141 raisin advanced selections in no spray plots were evaluated in August and September for powdery mildew (PM) resistance. Over 100 table and 36 raisin selections were free of mildew. Ninety-eight advanced table grape selections were evaluated and 29 noted for high fruit quality and resistance. Eleven new table grape selections were made and added to the advanced no spray plot for use as parents, representing 5 different sources of PM resistance. One DOV and 4 tray-dry raisin selections were propagated into production trials. Modified backcrosses combining high fruit quality with PM resistance were made. A total of 35 seedless x seedless, and 27 seeded x seedless table grape, and 25 seedless x seedless raisin crosses using a total of 57,373, 36,313, and 54,631 emasculations, respectively, were made. A total of 64 almond selections (42 self-compatible, 22 self-incompatible) as well as Nonpareil, Padre, Carmel (self-incompatible) and self-compatible Tuono were evaluated for shell and kernel characters. All remaining 2006 almond seedlings were evaluated for self-compatibility. A stakeholder meeting was conducted to provide growers and almond nurseries with information on breeding efforts to identify self-compatible almonds with Nonpareil-like kernel characteristics. Two self-compatible selections were identified through multivariate analysis as having kernel characteristics nearly identical with Nonpareil. Five self-compatible and two self-incompatible almond selections were propagated for production trials in the San Joaquin Valley.

4. Accomplishments
1. A single dominant powdery mildew resistance gene was identified in the Chinese grape species Vitus romanetii. Powdery mildew is the most important fungus attacking grapes worldwide. ARS researchers at Parlier, CA and Geneva, NY identified the gene by creating a number of table and raisin grape families segregating for powdery mildew resistance. The single dominant gene was readily scored for in-laboratory, greenhouse and field assays. It is expected that resistant raisin and table grapes may be developed with existing germplasm in 2 to 4 generations. Resistant grapes would reduce production costs, reduce yield losses and increase fruit quality.

2. Improved color retention in dried apricot. Dried apricots produced during early summer must endure half a year of storage before being sold during the winter holiday period. The color of dry apricots can darken dramatically during storage, with the degree of darkening being dependent on the particular apricot cultivar used. ARS apricot breeding efforts in Parlier, CA have led to the development of an apricot selection that holds color well in storage, even in non-refrigerated conditions. Color retention in the new selection was noticeably better than the standard apricot cultivar currently used for drying in California. Utilization of this new apricot selection would reduce dry apricot storage costs and ensure higher product quality for consumers.

3. Sunglo raisin grape released for production in Australia. Australian summer and fall rains cause fruit cracking, berry abscission and bunch rot resulting in lower yields and raisin quality. ARS researchers in Parlier, CA and Commonwealth Scientific and Industrial Research Organization (CSIRO) researchers in Merbein, Australia developed and tested the grape selection G4-74 and found the thick skin resisted cracking and produced quality raisins when treated with standard alkaline, oil-in water drying emulsions and rack drying. G4-74 (Sunglo) will provide Australian growers with a seedless, high yielding, rain tolerant raisin grape.

Review Publications
Ledbetter, C.A., Sisterson, M.S. 2010. Carpological variability of almond (Prunus dulcis [Mill.] D.A. Webb cv Nonpareil) in a single orchard during seven consecutive harvests. HortScience. 45(12):1788-1792.

Ramming, D.W., Gabler, F., Smilanick, J.L., Cadle Davidson, M., Barba, P., Consolie, N.H., Mahanil, S., Cadle Davidson, L.E. 2011. A single dominant locus Ren4 confers non-race-specific penetration resistance to grapevine powdery mildew. Phytopathology. 101(4):502-508.

Ledbetter, C.A. 2010. Almond breeding and evaluation activities in central California: past and future. Options Mediterraneennes. 94:255-260.

Siegel, J.P., Kuenen, L.P., Ledbetter, C.A. 2010. Variable development rate and survival of navel orangeworm (Lepidoptera: Pyralidae) on wheat bran diet and almonds. Journal of Economic Entomology. 103(4):1250-1257.

Riaz, S., Tenscher, A., Ramming, D.W., Walker, A. 2011. Using a limited mapping strategy to identify major QTL’s for resistance to grapevine powdery mildew (Erysiphe necator) and their use in marker-assisted breeding.. Theoretical and Applied Genetics. 122(6):1059-1073.

Last Modified: 06/26/2017
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