Quantitative trait loci identified for foliar phylloxera resistance in a hybrid grape population

Background and Aims: A hybrid grapevine biparental mapping population was evaluated for resistance to grape phylloxera (Daktulosphaira vitifoliae Fitch) in the greenhouse and in the field. The family (n = 125) was derived from a cross of two University of Minnesota breeding selections from a complex pedigree with multiple Vitis species. Methods and Results: The vines were evaluated for foliar phylloxera severity using visual rating in the field for multiple years. In the greenhouse, a replicated experimental design was used to quantify phylloxera severity using different traits including number of galls per plant, area under the disease progress curve, proportion of leaves with galls, average number of galls per leaf and visual rating. The plants used in the greenhouse experiment were also visually rated for root infestation. Conclusions: Quantitative trait loci (QTL) mapping for the foliar resistance traits (reduced severity) routinely identified the region spanning ~10 to 30 cM on linkage group (LG) 14 to be associated with resistance, and inherited from the mother parent MN1264. The plants used in the greenhouse experiment were also visually rated for root infestation, and subsequent QTL mapping identified regions on LG 5 of the maternal map and LG 10 of the paternal map (MN1246) associated with root resistance. Significance of the Study: The new QTLs identified in this report are potential novel sources of resistance and the first report of QTL for foliar phylloxera resistance in a hybrid grapegrowing region of North America. Molecular markers linked to resistance can be utilised in marker-assisted breeding.