Abstract
The association between reactive oxygen species (ROS) production and potato resistance to the hemibiotrophic pathogen Phytophthora infestans is poorly understood. In this study, the concentrations of hydrogen peroxide (H2O2), malondialdehyde (MDA), and soluble phenolics, as well as the activities of superoxide dismutase, catalase, and ascorbate peroxidase were measured during the early biotrophic and late necrotrophic stages of P. infestans infection on resistant and susceptible 'Ovatio' and 'Bintje' potato plants, respectively. Pathogen biomass was examined using semi-quantitative RT-PCR. Late blight (LB) severity was also evaluated. The LB severity in Ovatio was lower than that in Bintje, irrespective of the evaluation time. Moreover, in both cultivars, various biochemical defense responses occurred following pathogen infection. The susceptible cultivar activated defense responses at the later pathogen infection stages, resulting in higher concentrations of H2O2 and greater MDA content, with lower activity of antioxidant enzymes and phenolic content. These responses were accompanied by the necrotrophic phase, leading to extensive necrotic lesions on leaves. In contrast, fast hypersensitive-like lesions, an early peak in H2O2 concentration, low cell membrane integrity during the biotrophic phase, and a more efficient antioxidative system effectively restricted pathogen colonization before the transition to the necrotrophic phase in the resistant cultivar. These results suggest that LB resistance or susceptibility is regulated by a balance between the induction of ROS/antioxidants (intensity and timing) and the trophic phase of P. infestans.