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United States Department of Agriculture

Agricultural Research Service

Research Project: Develop Seedless Grapes for the Fresh Market Including Types Resistant to Powdery Mildew

Location: Crop Diseases, Pests and Genetics

2009 Annual Report


1a.Objectives (from AD-416)
Develop a series of seedless table grapes that ripen from early to late with white, black & red fruit. Fruit must meet shipping & storage requirements with high quality fruit. Emphasis will be placed on the development of early-ripening white grapes with large berry size, reduced hand thinning in the cluster, good sugar development & attractive appearance. Develop new table grape cultivars resistant to powdery mildew.


1b.Approach (from AD-416)
Standard breeding methods are being used. This consists of selecting varieties having the most desirable characteristics, hybridizing those varieties, selecting the best offspring and testing them as potential varieties. Tissue culture methods will be used to recover hybrids from seedless by seedless crosses. Advanced selections are tested in demonstration plots to determine commercial potential. Major areas of effort are for the development of seedless types to replace seeded varieties and varieties requiring high production costs. Powdery mildew resistance will also be incorporated into the table grapes from resistance germplasm. Selection for resistance will be done in the greenhouse and field where no fungicide applications are made. Documents Trust with CAL Table Grape Commission. Log 38313.


3.Progress Report

Powdery mildew resistant table grape cultivars are needed to reduce the need for chemical control. Modified backcrosses continued to combine high fruit quality from table selections with the best powdery mildew resistant selections. Over 250 mildew resistant table grape seedlings from twelve families screened for powdery mildew resistance in the greenhouse were planted in the field. Sixteen seedless x seedless crosses were accomplished in 2009 from which 575 ovules have been cultured. More than 81% of the 151 F1, BC1 and BC2 advanced selections that fruited in the no spray plots were completely free of mildew. Fourteen of these resistant selections had small, commercially acceptable seed traces. Ten new selections with small aborted seeds had good fruit quality and in some cases the natural berry size exceeded 5g. There is a continued need to improve seedless table grape cultivars so there is a good sequence of red, white and black fruit that ripen from early to late in the season to provide fresh grapes to the consumer for as long a period as possible. More than 1,100 table grape in vitro-derived seedlings from 37 seedless x seedless crosses were planted in the field. Thirty-six new seedless x seedless crosses were made in 2009 from which more than 21,000 ovules were cultured. Fifteen new seedless grape selections (9 red, 2 black, and 4 white) were the most promising and were propagated into 25 vine advanced test plot. One mid-season red, one early white, and one early black selections currently show commercial promise. Phenolic levels of skin and flesh from 27 table grape selections and cultivars ranged from 268 to 979 and 96 to 222 mg Gallic Acid Equivalent/100g flesh respectively. There was no correlation between skin and flesh phenolics. Antioxidant activity ranged from 1.896 to 6.421 and 0.091 to 0.583 mmol Trolox Equivalent Antioxidant Capacity/g in the skin and flesh, respectively. The project is monitored by the project leader through active involvement in the day-to-day research activities, and through regular on-site scheduled meetings with the Cooperator and interested stakeholders.


Last Modified: 12/22/2014
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