Silicon partially preserves the photosynthetic performance of rice plants infected by Monographella albescens

Leaf scald, caused by Monographella albescens, is one of the major diseases in rice worldwide. This study investigated the effect of silicon (Si) on the photosynthetic gas exchange parameters [net CO2 assimilation rate (A), stomatal conductance to water vapour (g(s)), transpiration rate (E)] and internal CO2 concentration (C-i), chlorophyll (Chl) fluorescence a parameters [minimal fluorescence (F-0), maximum fluorescence (F-m), maximum quantum yield of photosystem II (F-v/F-m)], photochemical quenching coefficient (q(p)), effective quantum yield of PSII [Y(II)], quantum yield of regulated energy dissipation [Y(NPQ)] and quantum yield dissipation non-regulated [Y(NO)] and the concentrations of pigments in rice plants grown in nutrient solutions containing either 0 (-Si) or 2 mM Si (+Si) and non-inoculated or inoculated with M. albescens. Leaf scald severity decreased with higher foliar Si concentration. For the inoculated +Si plants, A, g(s) and E were significantly higher in comparison with the inoculated -Si plants, in which C-i was significantly increased. Similarly, the concentrations of Chl(a), Chl(b), total Chl(a+b) and carotenoids were higher for the +Si plants in comparison with the -Si plants. Changes in the images of Chl a fluorescence were first observed precisely on the -Si plants leaves in comparison with the +Si plants. A decrease of q(P) and Y(II) in inoculated -Si plants, in comparison with the inoculated +Si plants, was accompanied by an increase in Y(NPQ) and Y(NO). Notably, the extent of the leaf areas was much more evident for Y(II) and q(P) in comparison with F-0, F-m and F-v/F-m, suggesting that Y(II) and q(P) were good predictors in detecting the early effects of leaf scald on the leaf photosynthesis. For the +Si non-inoculated plants, changes in Y(II) were associated with alterations in both Y(NPQ) and Y(NO) compared with non-inoculated -Si plants. In conclusion, the photosynthetic performance (as demonstrated by the gas exchange and Chl a fluorescence parameters) and the pigment pools of rice plants infected with M. albescens were preserved by Si supply and, therefore, provided an increase in rice resistance against leaf scald.