Pathotype dependent resistance mapping for powdery mildew in a diploid rose population

On a diploid segregating rose population (90 plants) disease resistance towards two powdery mildew pathotypes, R-E and R-P, were mapped. Different mechanisms of resistance were studied according to the nature of the parents: R. wichurana showed partial resistance to the pathotypes R-E and R-P; also ‘Yesterday’ shows some resistance to R-P, but is immune to R-E. Offspring plants were fingerprinted with 20 AFLP primer combinations and 43 SSR primers. By applying the F1-pseudo test cross population strategy for genetic map calculation, two parental linkage maps were constructed. The parental maps comprised 7 linkage groups for each parent and 264 and 306 number of markers, and covered 525 and 522 cM (Kosambi), for R. wichurana and ‘Yesterday’ respectively. QTLs for pathotype specific resistance were calculated from the segregation patterns of resistance reactions in the offspring plants. The identification of QTLs in genomic regions involved in pathotype specific resistance can serve as a helpful tool for analyzing underlying mechanisms for disease resistance and finally for pyramiding QTLs with different resistance effects in roses.