An overview of the position and robustness of scab resistance QTLs and major genes by aligning genetic maps of five apple progenies

In the frame of the D.A.R.E. project, five mapping populations have been studied for partial scab resistance against several races of Venturia inaequalis. A main objective was to identify QTLs (quantitative traits loci) with broad spectrum of resistance towards a wide range of strains of the fungus. Genetic markers (mainly SSR and AFLP) were tested on each population and genetic maps were constructed for both parents of each population. Meanwhile, pathological tests with several isolates of different races of V inaequalis were performed. Four major genomic regions appear to be involved in scab resistance: they are located on linkage groups (LG) LG-1, LG-2, LG-11, and LG-17. Some other linkage groups carry either QTLs or major resistance genes that are isolate specific: a QTL on LG-5, Vd on LG-10, and Vg on LG-12. The QTL region located on LG-17 clearly exhibited the widest spectrum of resistance.