We analyzed powdery mildew resistance in 272 vines from the cross between Horizon (susceptible) and Ill. 547-1 (resistant). Segregation for resistance was normally distributed. Our work shows that the actual distance between two DNA markers for powdery mildew resistance identified earlier is actually 12 cM, rather than the 1.8 cM calculated earlier from a small population.
As a result of bulked segregant analysis using AFLP markers, we found 68 candidate markers for mapping to the powdery mildew resistance locus. Efforts have begun to saturate the genetic map in the region of this resistance gene locus. To date, 57 of the 68 markers were examined, yet of these just seven were tentatively placed on the map in the same region as the powdery mildew resistance locus.
New technologies are being developed in other laboratories that may allow a more thorough and detailed analysis of the many genes involved in a plant’s defense again disease. Our project to date has been focused on just a single gene (or a chromosomal region with several genes). Given the relative difficulty to clone even a single gene based on map position, I have decided to pause this project pending examination of the best techniques currently available to reach our goal of cloning grapevine genes for disease resistance and understanding more about the grapevine disease resistance responses. Undoubtedly, the material we now possess is unique, and our present knowledge of the map location of this gene for powdery mildew resistance will be of value as new approaches are examined to reach our original goals.