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United States Department of Agriculture

Agricultural Research Service


Location: Grape Genetics Research

2009 Annual Report

1a. Objectives (from AD-416)
1. Develop improved genetic systems for functional genomics research of grape pest and disease resistance. 2. Characterize the genetic, genomic, proteomic, and other aspects of the interaction of grapevines and fungal and oomycete pathogens to identify the key determinants of resistance, tolerance, and susceptibility. 3. Improve grapevine rootstocks through identification, development, deployment, and enhancement of resistance to pests and diseases.

1b. Approach (from AD-416)
Develop a grapevine system with reduced juvenile period for rapid candidate gene evaluation of disease and pest resistance. Optimize and evaluate the utility of a newly created dwarf grapevine system for investigating interactions between grapevines and key pests and pathogens. Determine race-specificity of powdery mildew resistance in Vitis species. Develop molecular markers associated with resistance to grape powdery mildew. Characterize the relationship between biochemical changes in the berry-powdery mildew interface and developmentally-regulated resistance to powdery mildew on grape berries. Enhance non-race-specific resistance in Vitis vinifera to powdery mildew and/or downy mildew via knock-out of susceptibility loci. Characterize the genetic control of resistance to Meloidogyne species (root-knot nematodes) in grapevine. Develop molecular markers associated with resistance to root-knot nematodes. Develop grape rootstocks with enhanced resistance to root-knot nematodes. Evaluate the ability of rootstocks to mitigate symptoms of Pierce’s disease in grapevine rootstocks. Develop autotetraploid selections with reduced vigor induction and evaluate their pest resistance.

3. Progress Report
Powdery mildew and downy mildew are serious grapevine pathogens that reduce grape yield and quality. To help U.S. grape breeders select for resistance to mildews, more than 850 advanced breeding lines, cultivars, and segregating progeny (over 10,000 replicate samples) were screened. In order to identify easily propagated candidate rootstocks, 156 selections resistant to aggressive virulent root-knot nematode populations were tested for rooting ability under greenhouse conditions. Of the selections tested, 142 rooted at 70% or above without the addition of rooting hormones or bottom heat. These selections are candidates for additional root-knot nematode resistance evaluation and horticultural evaluation. Developed a transgenic hairy root system for evaluating genes in grapevine roots. We evaluated the responses of 14 grape species to inoculation with three Agrobacterium strains and observed that two of the grape species responded to the inoculation positively in producing hairy roots. These results will lead to the development of a hairy root testing system for high through-put evaluation of genes that may confer grapevine resistance to root-knot nematodes and other root pests and diseases. In order to develop a small, easily transformed grapevine variety, we evaluated several plant-growth related genes including VvGAI, VvFT and AtBRC1 in the model plant Arabidopsis. We observed that these genes had significant impact on plant heights and other growth traits. This knowledge will help us to design a better strategy for creating a new grapevine variety for functional genomics research. Demonstrated flowering of interspecific hybrid populations of grapevine seedlings as preciously as the 10th node above the cotyledons. These seedlings were grown in a greenhouse and did not receive chilling hours or dormancy, typically required for regular flowering in physiologically mature grapevines. Selected individual seedlings show continuous flowering from latent buds under greenhouse conditions and can be propagated in tissue culture, which will facilitate their utilization in genomics and breeding research. To identify the genetic control of resistance against aggressive virulent root-knot nematodes, the allelism of putative new allele for nematode resistance inherited from Vitis rufotomentosa Small was tested to determine its relationship to the N allele. Based on progeny testing, the novel allele from V. rufotomentosa is not allelic to the N allele sensu Lider (found in Harmony and Freedom rootstocks). The independent assortment of the nematode resistance alleles indicates that the N allele and the V. rufotomenstosa allele represent forms of different genes. The V. rufotomenstosa allele provides protection to a broader range of nematode populations than does the N allele and is deployed in nematode resistant rootstock selections. Determination of the independent and non-allelic nature of the N and the V. rufotomenstosa allele will facilitate breeding superior nematode resistant rootstocks and allow gene pyramiding to enhance durability of resistance.

4. Accomplishments
1. Molecular marker developed for seedlessness and disease resistance. New cultivars of seedless table grapes require embryo rescue by tissue culture and several years of growth in order to evaluate seedlessness. A new molecular marker was developed that predicts seedlessness, allowing breeders to select seedless types early after embryo rescue and discard seeded grapevines without investing resources in their maintenance and evaluation. In addition, a marker for a broad spectrum powdery mildew resistance locus was discovered in the same breeding material. In addition to the scientific progress toward isolating and characterizing these genes, the molecular markers will accelerate the selection of seedless grapes with disease resistance, which will allow growers of these future cultivars to drastically reduce pesticide applications. Varieties bred with the broad spectrum powdery mildew resistance would save growers between $100 to 400 per acre per year in pesticide costs and reduce direct and indirect effects of pesticide application.

Last Modified: 06/22/2017
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