Location: Grape Genetics Research2012 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:
DNA molecular markers can be used to track genes and positive alleles in breeding programs. We adapted a high resolution DNA marker platform called Genotyping-by-Sequencing (GBS) to identify genes underlying traits and to apply markers for selection in grape breeding programs. The GBS technology increased marker resolution 10-fold over previous high resolution marker platforms and 100-fold over standard SSR marker platforms, with a low per-sample cost. In 2012, we confirmed linkages of GBS markers with powdery mildew resistance and seedlessness. We applied GBS markers in over 6000 grape breeding progeny to identify elite seedlings for focused evaluation. Some muscadine grapevines (Vitis rotundifolia) from the Southeastern U.S. are naturally resistant to powdery mildew infection due to the Run1 resistance gene. In NY, we observed signs of powdery mildew infection on Run1-containing vines, even though the pathogen population had never been exposed to muscadine grapevines or the Run1 resistance gene until the past decade. We collected isolates of the powdery mildew fungus and evaluated their interaction with grapevines carrying the Run1 gene. The powdery mildew isolates could grow well on these grapevines, but not on grapevines with other resistance genes. When Run1 was combined with other resistance genes, powdery mildew was effectively halted. These results are guiding grape breeders, grape pathologists, and grape growers to protect Run1 for future generations. Around the world, early season epidemics of grape powdery mildew progress more slowly than predicted. We showed that pre-treatment of susceptible grape leaves by exposure to cool, springtime temperatures (eg, 4 to 8°C for as little as 5 minutes) reduced powdery mildew disease. This may partly account for discrepancies in disease forecast modeling. Historical weather data indicated that early-season cold events in this temperature range occur commonly across most viticulture regions worldwide, and may partially explain: unexpectedly slow development of powdery mildew during the first month after budbreak, and the sudden increase in epidemic development once seasonal temperatures increase above the threshold for acute cold events. This knowledge may reduce the number of pesticide sprays and improve disease forecasting models. Genotyping microarrays are a common technology used to assay genetic variation. These arrays rely on the matching of a sample’s DNA to a sequence from a reference plant. High diversity plant species such as grapevine, data from the array can be difficult to interpret. We developed a genetic mapping method that is easy to compute and can be used in any mapping population for which genotyping microarray data have been collected. We demonstrated its use in mapping three simple traits (color, flower sex and resistance to powdery mildew) in grapevine by using raw fluorescence data instead of software-generated sequence predictions, and with population sizes smaller than previously used. This advance will reduce the cost and increase the impact of genotyping microarrays in high diversity species, which includes many of the plants we rely on for food.
1. Three lines of low vigor grapevine rootstocks. Rootstocks that provide protection against pests and diseases are a sustainable method for managing damage to grapevine roots. Rootstocks influence the size and growth rate of the fruitful scion varieties grafted on them. Some rootstock varieties are too vigorous for certain fertile vineyard soils, but these rootstocks have useful or unique pest and disease resistance. ARS researchers at Geneva, New York invented three selections of a useful but highly invigorating grapevine rootstock that are slower growing with shorter internodes than their diploid progenitor and are expected to produce lower vigor and lower vine size in fruitful scions grafted on them. Special nursery propagation, production, and grafting methods will be needed for commercialization of these selections. A Material Transfer Agreement with a leading grapevine nursery is in place for these three lines.
2. Dwarf grapevines. ARS researchers at Geneva, New York developed the Pixie dwarf grapevine variety in cooperation with the University of California and released the variety in 2007. The Pixie dwarf grapevine is gibberellic acid insensitive. Pixie grapevines have very short internodes and produce inflorescences in preference to tendrils. Seedlings carrying the semidominant dwarfing gene inherited from Pixie can begin to flower in as few as three months. We used Pixie as a pollen parent in crosses with rootstocks to develop three lines of dwarf grapevines. These dwarf grapevines are more vigorous than Pixie, showing faster growth, but the vines are still compact and show inflorescences in preference to tendrils. The three new lines of dwarf grapevines are pistillate flowered, with only functional female parts. This is in contrast to the Pixie grapevine, which is self fertile, self pollinating, and has functional male and female parts. Since the new lines are pistillate flowered, they can easily be used in hybridization with other grapevine varieties. The new lines flower continuously when cultivated in a greenhouse. One of the lines carries the N allele for root-knot nematode resistance inherited from Freedom rootstock. The new lines of dwarf grapevine could be useful for breeding and genetics studies and as parent material for grapevine rootstocks.
Mahanil, S., Ramming, D.W., Cadle-Davidson, M., Owens, C.L., Garris, A., Myles, S., Cadle Davidson, L.E. 2012. Development of marker sets useful in the early selection of Ren4 powdery mildew resistance and seedlessness for table and raisin grape breeding. Journal of Theoretical and Applied Genetics. 124:23-33.