EXAMINATION OF MARKER-ASSISTED SELECTION FOR POWDERY AND DOWNY MILDEW RESISTANCE

Abstract

Field grown seedlings potentially carrying both the Run1 and Rpv1 loci for powdery and downy mildew resistance, respectively, from muscadine (Vitis rotundifolia) introgressions were assessed for resistance to both powdery and downy mildew. Powdery mildew was assessed in the field under no-spray conditions, while downy mildew was assessed using a detached leaf assay in vitro. In these populations, markers for the Run1 gene were excellent predictors of powdery mildew resistance, but markers for the Rpv1 gene were not useful in predicting downy mildew resistance. Markers for Ren2 powdery mildew resistance derived from Vitis cinerea were also useful. Populations that were previously selected for powdery mildew resistance (where the susceptible types had already been discarded) had a very high frequency of markers for the Run1 gene and/or the V. cinerea source of resistance, confirming the success of field screening techniques. By screening for the presence of markers, it was possible to identify seedlings harboring both the V. cinerea as well as muscadine sources of powdery mildew resistance.