Fungicides, bio-controllers and resistance inducers affect bioactive compounds and oxidative metabolism in bell pepper plants inoculated with Phytophthora capsici

The rational use of chemical fungicides in chilli pepper (Capsicum annuum L.) for controlling Phytophthora capsici Leo. should include molecules that promote induced systemic resistance in the plant. The study objective was to assess how the application of fungicides, bio-controllers and resistance inducers affects bioactive compounds production and oxidative metabolism in pepper plants when inoculated with P. capsici zoospores. Statistical analyses show significant differences in total flavonoids, total phenols and salicylic acid concentrations in plants treated with Trichoderma harzianum, Acibenzolar-S-Methyl (ASM) and phosphonic acid. In addition, the application of ASM and Bacillus subtilis showed the highest values of antioxidant capacity. On the other hand, ASM application favoured increases in superoxide dismutase and phenyl ammonium lyase activity with values of 4.42 ± 0.016 (units · min⁻¹ · g⁻¹) and 3.90 ± 0.22 U · g⁻¹, respectively. However, hydrogen peroxide production was similar to that of phosphonic acid treatments. Similarly, plants treated with B. subtilis and Metalaxyl-M showed increases in peroxidase enzyme activity with values ranging from 2.86 ± 0.05 to 4.52 ± 0.02 (μmol · [mg protein]⁻¹ · min⁻¹). Likewise, phosphonic acid-treated plants exhibited high catalase enzyme activity with values ranging from 2.38 ± 0.032 μmol H₂O₂ · min⁻¹ · g⁻¹ to 4.30 ± 0.024 μmol H₂O₂ · min⁻¹ · g⁻¹. The complementary use of products with biological and resistance-inducing functions could help to mitigate the environmental impacts that occur due to the use of chemical fungicides for controlling P. capsici on chilli pepper.