Construction of a genetic linkage map with SSR, AFLP and morphological markers to locate QTLs controlling pathotype-specific powdery mildew resistance in diploid roses

Disease resistance is a sought-after trait in plant breeding programmes. One strategy to make resistance more durable is to increase the number of resistance genes, thereby increasing the number of pathotypes withstood. One of the most important diseases on roses is powdery mildew (Podosphaera pannosa). Recent studies show that pathotypes of powdery mildew and different types of resistances in roses exist. The results of this study aim to contribute to powdery mildew resistance in roses by the development of pathotype-specific markers on a genetic map. A diploid rose population (90 genotypes) derived from a cross between R. wichurana and Rosa ‘Yesterday’ was used to construct a genetic linkage map encompassing 20 AFLP primer combinations, 43 SSR, and 2 morphological markers. By applying the F1 pseudo test cross population strategy, 2 parental linkage maps were constructed (parent ‘Yesterday’ 563 cM; parent R. wichurana 526 cM). Both parental maps consisted of 7 linkage groups with an average length of 70 cM (Kosambi) corresponding to the 7 haploid rose chromosomes. These new maps were used to identify QTLs controlling disease resistance. The offspring population was screened for resistance to 2 powdery mildew pathotypes, R-E and R-P. QTLs for controlling pathotype-specific disease resistance were mapped by applying Kruskal-Wallis rank-sum tests and simple interval mapping. With 2 pathotypes analysed, 9 QTL loci were detected on linkage groups 2, 3, 5 and 6, explaining 15-73% of the phenotypic variance for pathotype-specific disease response. The genetic maps developed here will be useful for future rose breeding, pathotype-specific resistance research and development of a consensus map for roses.