QTL Analysis of Powdery Mildew Resistance in Grapes

Dalbo, M.A., Ye, G.N. Weeden, N.F., and Reisch, B.I. 1997. QTL mapping of powdery mildew resistance in grapes. Plant and Animal Genome V. 12-16 January 1997, San Diego, CA, USA (abstr.).

New York State Agricultural Experiment Station, Cornell University, Geneva, New York 14456, USA

Commercial grape (Vitis vinifera) cultivars are susceptible to powdery mildew but resistance is present in related species. Molecular markers associated with mildew resistance loci can be useful in the breeding of resistant cultivars. We studied the inheritance of powdery mildew resistance for 6 years in the cross 'Horizon' (complex hybrid) x Illinois 547-1 (V. rupestris x V. cinerea). A genetic map based on RAPD markers was constructed for each parent. These maps have more than 180 markers each, with a mean distance between markers of 5.5 cM. QTL analysis was done with qGene software. A major QTL was found in Illinois 547-1, the resistant parent. Bulked Segregant Analysis was used to screen 203 primers to find additional linked RAPD markers. A single marker (S25b; LOD=6.9) explained 44% of the variation. The same marker was present in V. cinerea B9, one of the parents of Illinois 547-1 and the likely source of resistance. Two other regions in the 'Horizon' map showed some association to resistance. The markers S25b (from Ill. 547-1) and S35a (from 'Horizon') could be used to correctly classify all but 9 of 60 seedlings. This work confirms that resistance to powdery mildew is polygenic but major genes or gene clusters are involved. Further plans to utilize marker-assisted selection include the development of SCAR markers for testing in related and unrelated populations.

Abstract, Plant and Animal Genome V, January, 1997, San Diego, California.