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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING GRAPE ROOTSTOCK AND SCION PEST AND DISEASE RESISTANCE

Location: Grape Genetics Research

2011 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
Understanding how rootstocks and scions interact is important for grape production and variety development. To determine whether or not dwarf phenotype can be transmitted from rootstocks to scions, Pixie, a dwarf grapevine, was used as rootstock and grafted to Thompson Seedless, which has a normal plant stature. No dwarf phenotype was observed in the scion of the grafted plants. This result was in contrast with what was observed in apples in which dwarf rootstocks can pass their dwarf characteristics to scions. The result suggested that rootstock-scion interactions were trait- and species-specific.

Whole plant functional testing of grapevine genes is challenging due to large plant size and the time required from transformation to fruiting. In order to develop a small, rapid cycling, and easily transformed grapevine variety, we introduced several plant-growth related genes including VvGAI, VvFT and AtBRC1 into grapevines to determine how these genes affect plant architecture and growth. We observed that these genes significantly impacted plant height, branching and other growth and development traits. This knowledge will help us create new varieties with improved architecture and other growth and development traits for functional genomics research as well as variety improvement.

We are interested in exploring the feasibility of developing a biotech solution for controlling root-knot nematodes in grapevines. We developed a transgenic hairy root system for evaluating root-knot nematode resistance genes in grape. We characterized the responses of 14 grape species to the inoculation of 3 Agrobacterium strains and observed that Agrobacterium strains, plant genotypes, and inoculation sites all significantly impacted the success of inducing hairy roots. An optimized hairy-root induction system was established and is being used as a high through-put system for evaluation of genes conferring nematode resistance to grapes.

To develop new cultivars with disease resistance, we used molecular markers to screen 1704 breeding progeny from 20 independent cross-hybridizations. These markers, genetically linked with known disease resistance genes, enabled selection of progeny with multiple disease resistance genes, for improved durability and breadth of resistance.

Grapevine seedlings often do not flower until after several seasons. This growth habit limits the progress of genetics and breeding research, since such research is often limited by generation time. In a cross of a precocious flowering grapevine with a rootstock, we demonstrated that precocious flowering is conditioned by a single semi-dominant allele. The population segregated for leaf disk color/berry flesh color and flower sex type in addition to precocious flowering. Since more grandparental phenotypes were recovered than would be expected randomly, it may be that precocious flowering is genetically linked to flower sex and leaf disk color, although this could be an artifact of flower sex type on sexual maturation. This research enables grape breeders to use the publically available germplasm to more specifically address accelerating population improvement and genetics research.


4.Accomplishments
1. Identified important grape powdery mildew genes. Although powdery mildew is economically the most important fungal pathogen of grapevines, it cannot be grown in pure culture, thereby limiting knowledge about its genetics. In order to identify and target weaknesses in powdery mildew biology, ARS researchers at Geneva, NY, sequenced and described all of the genes expressed by grape powdery mildew, as part of an international collaboration spanning powdery mildews of fruits, vegetables, grasses, and weeds. Researchers discovered powdery mildew genes required for reproduction, cold survival, and fungicide tolerance. This improved knowledge of powdery mildew genetics provides new targets for disease management of a fungus that costs grape growers $100 to 400 per acre per year.

2. Released three new nematode resistant rootstocks. Root-knot nematodes are a chief pest of vineyards across California and the United States. Resistant rootstocks provide protection against nematodes and are an alternative to pesticides. ARS researchers at Geneva, NY, used cross breeding to combine nematode resistance and useful traits into new rootstock selections and evaluated pest resistance, viticultural performance, and other important qualities to identify candidate rootstocks. Three improved root-knot nematode resistant rootstocks, ‘Matador’, ‘Minotaur’, and ‘Kingfisher’, were released in 2010. These nematode resistant rootstocks demonstrate improved yield efficiency when compared to Freedom rootstock, an industry standard, with more yield of grapes in relation to weight of cane prunings. All three rootstocks are available as virus tested plant material from the University of California, Foundation Plant Services; grapevine nurseries have acquired these varieties for commercial increase blocks.

3. Released precocious flowering grape variety for breeding and genetics research. Grapevine genetics and breeding is slower than in other crop plants because grapevines usually need three to four years before they flower and fruit. ‘Scout’ is a new grape variety that provides accelerated flowering for breeding and genetics research. ‘Scout’ was developed by ARS researchers at Geneva, NY, from a cross of ‘Rubired’ wine grape with a wild grape species. ‘Scout’ grapevine seedlings may flower in as few as 100 days from seed. The development of this new variety will greatly accelerate grape breeding progress for economically important traits. ‘Scout’ vines flowers profusely and continuously in a greenhouse. ‘Scout’ develops deep red color in leaf disk assays; this trait can be used to demonstrate hybrid parentage of populations. ‘Scout’ is a male flowered vine, but seedlings can be self fertile or male flowered.


Review Publications
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.

Wakefield, L., Gadoury, D.M., Seem, R.C., Milgroom, M.G., Sun, Q., Cadle Davidson, L.E. 2011. Differential gene expression during conidiation in the grape powdery mildew fungus, Erysiphe necator. Phytopathology. 101:839-846.

Gadoury, D., Cadle Davidson, L.E., Wilcox, W., Dry, I., Seem, R., Milgroom, M. 2012. Grapevine powdery mildew (Erysiphe necator): a fascinating system for the study of the biology, ecology, and epidemiology of an obligate biotroph. Molecular Plant Pathology. 13:1-16.

Brewer, M.T., Cadle Davidson, L.E., Cortesi, P., Spanu, P.D., Milgroom, M.G. 2011. Identification and structure of the mating-type locus and development of PCR-based markers for mating type in powdery mildew fungi. Fungal Genetics and Biology. 48:704-713.

Last Modified: 9/10/2014
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