H2O2 accumulation plays critical role in black spot disease resistance in roses

Most rose cultivars are susceptible to black spot disease caused by Marssonina rosae. To elucidate the effect of leaf structure, callose deposition and H2O2 metabolism on black spot disease resistance, we measured the wax content and cuticle thicknesses of leaves, the callose, H2O2 accumulation, and the SOD, POD, APX and CAT activity and their related gene expression levels in six Rosa species and cultivars infected with M. rosae. The correlation between black spot disease resistance and leaf structure, callose, and H2O2 accumulation, and the role of H2O2 in response to black spot disease were analyzed. The results showed that black spot disease resistance was closely related to H2O2 accumulation, and there was a strong significant negative correlation between disease resistance and H2O2 accumulation (P < 0.01). APX, CAT and POD activity and their related gene expression levels, which are related to H2O2 accumulation, were higher in resistant accessions than in susceptible accessions in the early stage of the plant-pathogen interaction. An increase in H2O2 appeared and antioxidant enzymatic activities increased at the late stage of infection with M. rosae in susceptible accessions, which was different from the trend in resistant accessions. Our results demonstrate that an early and rapid response to H2O2 accumulation in black spot disease-resistant rose accessions could be one of the reasons for resistance against M. rosae. Therefore, regulation of ROS during the early response could be a feasible approach for achieving black spot disease resistance in roses.