To analyse the inheritance of fruit ring rot (FRR) resistance and to screen for microsatellite markers linked to resistance⁄susceptibility, 875 apple hybrid seedlings (Malus domestica, Jonathan · Golden Delicious) were inoculated with five isolates of Botryosphaeria dothidea in 2 years (2008 and 2009). The results indicated that incidence and non-incidence were qualitatively segregated, and incidence was dominant to non-incidence. The variation in susceptibility within this population was attributed to the segregation of three major genes. For the phenotype of incidence, the severity of lesion development was a quantitative trait. From 230 published microsatellite primer pairs, six markers were identified that were linked to the susceptibility to FRR. located in LG12 and LG2, respectively, were linked to susceptibility to the pathogen isolate Mx1, and their map distances to the susceptibility loci were 8.2 and 5.1 centimorgan (cM), respectively. CH01e01-120 and CH02c02b-100, which were linked to susceptibility to Ls1, were located in LG14 and LG4, and the map distances to the susceptibility loci were 16.9 and 8.4 cM, respectively. CH05d11-150 and CH03a03-230, linked to susceptibility to Lw048, were located in LG12 and LG14; for both of them, the map distance was 13.4 cM.

The resistance of 240 Malus germplasm accessions to bot canker was evaluated by inoculating branches in the field with cultured mycelia from five pathogenic isolates of Botryosphaeria dothidea. Differences in the disease resistance were significant among the examined germplasm accessions and the different pathogenic isolates. In general, the resistance of the wild species and the Chinese domestic cultivars was much stronger than that of the cultivars or mutants of Malus · domestica. Baccata HR, a genotype from a wild species, is highly resistant. Three M. · domestica cultivars ⁄ mutants, Maypole, Spy227 and Fengyan, are resistant, whereas Changhong is highly susceptible. A wide range of resistance levels were observed among the 28 M. sieversii genotypes. Differences in resistance were also found among clonal mutants from cultivars of M. · domestica. The disease indices of the same germplasm in response to different pathogenic isolates of B. dothidea are sometimes significantly different.