Silicon complements disease control by fungicides by enhancing the biochemical defense responses of barley against Bipolaris sorokiniana

Spot blotch (caused by Bipolaris sorokiniana) is one of the main diseases of barley. In this study we evaluated the effect of silicon (Si) combined with the preventive application of a fungicide on the biochemical defense against spot blotch. For this purpose, we evaluated the activity of antioxidant system enzymes, accumulation of total soluble phenolics (TSPs), the lignin derivatives thioglycolic acid (DLTGA), and their influence in the host membrane damage by determining the electrolyte leakage (EL). Two barley cultivars, AnaG01 and BRS Caue, both susceptible, were grown in soil not supplied (-Si) or supplied (+ Si) with Si and treated with the fungicide 7 or 15 days before inoculation (dbi). The highest disease severity (up to 29%) was observed for the -Si plants not treated with fungicide. Plants supplied with Si showed lower disease intensity due to an increase in the activity of SOD and reduction in CAT, which may have favored the hydrogen peroxide accumulation as well as increases in the TSP and DLTGA concentrations. The best disease control was achieved by combining Si in the soil and fungicide spray, especially when application occurred at 7 dbi. Furthermore, this combination increased the control at 15 dbi compared to -Si plants, indicating that defense mechanisms enhanced by Si may have favored the fungicidal control at the end of the protective period, reducing the disease intensity. In conclusion, the results of this study showed that Si supply to barley plants promoted the activation of biochemical mechanisms related to the plants' defense, enhancing the control of spot blotch severity by the fungicide.