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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

2010 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
Twelve apricot selections were bagged for self-(in) compatibility status. Six apricot cultivars varying in bloom dates were planted in Riverside County, CA to determine fruitfulness in a low-chill environment. Twelve advanced apricot selections of Central Asian-California parentage were propagated for continued evaluations. A rootstock trial (Nemaguard vs. Citation) was established to evaluate differences in tree performance and apricot fruit quality in nine cultivars and advanced selections. Three plum, 10 peach and 11 nectarine selections were propagated for virus testing.

Ninety percent of the BC1 grape population for red flesh was evaluated for flesh color and correlation with a leaf disk assay. Initial tests to determine inheritance of red flesh were run. Over 500 seedlings for studying the natural dry-on-the-vine (DOV) raisin trait were harvested for moisture determination. Fresh fruit from the DOV parents and two control cultivars (Thompson Seedless and Summer Muscat) were tested for drying rates under controlled conditions. Skin wax and cuticle thickness were evaluated to determine if this affected speed of drying. Sixty-five DOV raisin selections were harvested for yield, and 35 were dry enough to harvest by October 1. Twelve produced more than 4 kg raisins/vine and four had >90% B or better grade raisins. The most advanced DOV selection continued to dry by October 1 with good yield and raisin quality.

After evaluating seedlings for powdery mildew resistance and fruit quality, nine table grape, nine raisin and 14 DOV raisin selections were propagated for production trials. One table grape selection was propagated for comparison with current table grape cultivars. Seedlings from both seedless x seedless crosses and seed were evaluated for powdery mildew resistance, with only resistant plants being transplanted. Seedlings for genetic studies were also evaluated for powdery mildew and leaf samples were collected for DNA analyses. Over 1,300 seedlings from 17 families and 3 powdery mildew resistance sources were evaluated for infection levels on the leaves, stems, rachis and fruit. Leaf samples were collected for analyses examining molecular markers associated with resistance. Over 400 advanced table grape and raisin selections were evaluated twice for mildew resistance in the no spray plots.

A total of 94 almond selections (63 self-compatible, 31 self-incompatible) as well as Nonpareil, Padre, Carmel (self-incompatible) and self-compatible Tuono were evaluated for shell and kernel characters. Three 6 kg in-shell almond samples from promising self-compatible accessions were shown to the Almond Board of California for independent evaluations of shells and kernels. During the 2010 bloom, 26 almonds were bagged to determine ability to set fruit without bee visitation. Nine trees were found to be sufficiently self-fruitful to warrant retention. Multiple flowering branches of advanced self-compatible selections provided to the Almond Board were also bagged, and their self-fruitfulness was re-confirmed during the 2010 bloom period.


4.Accomplishments
1. Growers have new rootstock options for stone fruits and almonds. A successful orchard requires trees having a rootstock that can resist infection of soil-borne diseases and pests as well as providing trees with water and nutrients necessary for a bountiful harvest. When an orchard is replanted with the same rootstock as was previously used, tree vigor can suffer and yields are generally reduced. ARS researchers at Parlier, CA teamed with University of California Davis scientists to develop three new clonal rootstocks that are compatible with stone fruits and almonds. The new rootstocks are resistant to the prevalent root knot nematode, and produce trees of slightly smaller stature, but fruit/nut bearing capability is not affected. Growers can expect enhanced growth of young trees when these rootstocks are utilized in previously planted orchard sites. An additional benefit lies in reduced pruning costs throughout the life of the orchard.

2. Leaf disk assay used to detect grapes with red flesh. Anthocyanins are considered an excellent source of antioxidant phytochemicals for health benefits. Only a few wine grapes and no table or raisin grapes have anthocyanins in their flesh. ARS researchers at Parlier, CA hybridized a red flesh wine grape with a table grape, selected seedlings with red flesh and crossed them to table and raisin grapes. Leaf disks of plants less than 6 months old were cultured in sugar solution. Rapid pigment development in leaf disks was associated with red flesh. This allows selection of plants with red flesh several years before plants produce fruit facilitating breeding of table and raisin grapes with red flesh and higher levels of antioxidants.


Review Publications
Ledbetter, C.A. 2010. ‘Bolaroja’ and ‘Primarosa’: Two New Mid Season Apricots for the Fresh Market. HortScience. 45(3): 441-442.

Ramming, D.W. 2010. Greenhouse Screening of Grape Rootstock Populations to Determine Inheritance of Resistance to Phylloxera. American Journal of Enology and Viticulture. 61(2):234-239.

Breksa III, A.P., Takeoka, G.R., Hidalgo, M., Vilches, A.M., Vasse, J., Ramming, D.W. 2010. Phenolic Content of Raisin Grape Varieties and Genotypes. Food Chemistry. 121, 740-745.

Ledbetter, C.A. 2010. Register of New Fruit and Nut Varieties List 45. HortScience. 45(5):716-756.

Klasson, K.T., Ledbetter, C.A., Wartelle, L.H., Lingle, S.E. 2010. Feasibility of dibromochloropropane (DBCP) and trichloroethylene (TCE) adsorption onto activated carbons made from nut shells of different almond varieties. Industrial Crops and Products. 31:261-265.

Last Modified: 9/2/2014
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