Photosynthetic gas exchange and antioxidative system in common bean plants infected by Colletotrichum lindemuthianum and supplied with silicon

This study investigated the effects of silicon (Si) on the resistance of common bean plants to anthracnose caused by Colletotrichum lindemuthianum. The plants were grown in a nutrient solution containing 0 (control) or 2 mM Si (+ Si) and both photosynthesis and antioxidative metabolism levels were evaluated. The Si concentrations in the leaf tissues of + Si plants increased by 33% in comparison to those of control plants. Anthracnose severity was reduced by 34% in + Si plants in comparison to control plants. The net carbon assimilation rate, stomatal conductance to water vapor and transpiration rate values were significantly higher in + Si plants than in control plants. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) tended to be higher in + Si plants than in control plants. The hydrogen peroxide concentration was significantly lower in + Si plants than in control plants. In conclusion, the Si supply was associated with lower anthracnose severity and up-regulation of antioxidant enzymes, which in turn might be associated with better gas exchange in + Si plants. The impaired photosynthetic performance in + Si plants was associated with stomatal limitations, whereas in control plants those impairments likely reflected dysfunctions at the level of biochemical reactions involved in CO2 fixation.