Host defense responses during powdery mildew ( Golovinomyces latisporus comb. nov.) infection in sunflower ( Helianthus annuus L.)

The infection by a plant pathogen results in the production of the reactive oxygen intermediates (ROIs) in the plant. ROIs threshold levels determine the fate of the resistance in the host; higher than the threshold levels result in the appearance of the resistant or susceptible reaction on the infected plants. ROIs below the threshold levels have been shown to be important in eliciting disease resistance-related signaling pathways that result in the production of antimicrobial compounds, pathogenesis-related proteins, cell wall cross-linking. Golovinomyces latisporus is a very important biotrophic pathogen on sunflower causing powdery mildew disease, which causes serious yield losses. A set of genotypes confirmed earlier to be susceptible (PS 2023 and Morden) and resistant (TX 16R and ID-25) were analyzed for disease progression after the pathogen infection and the development of oxidative burst. In comparison, susceptible genotypes exhibited higher levels of ROIs than resistant genotypes, thus indicating the importance of these molecules in the infection process. The higher levels of ROIs in susceptible genotypes lead to cell damage. Concomitantly, the anti-oxidant enzyme activities are significantly higher in the resistant genotypes than in the susceptible genotypes. The resistant genotypes displayed higher levels of transcripts of hsr203J , which has proven roles in cell death, and NPR1, the master regulator of the salicylic acid-based resistance signaling that acts in plants resistance against biotrophic pathogens.