Analyzing the role of acibenzolar-s-methyl as a possible inducer of resistance against root rot disease and the decline in melon branches

Due to the great limitations in the control of melon (Cucumis melo L.) diseases and taking into account the great importance of resistance inducers, this work aimed to evaluate the effects of pre- and post-sowing application of ASM (acibenzolar-S-methyl) on physical and biochemical characteristics against melon root rot disease and vine decline caused by the pathogen Macrophomina spp. The experiment was carried out in a greenhouse as well as in the laboratory, in a completely randomized design with seven treatments (positive control; negative control; seed treatment; aerial part application; soil application; seed treatment plus aerial part application; and seeds plus soil application) and five replications. For the positive control, only the naturally infested soil without ASM application was used; for the negative control, soil was autoclaved; and for the other treatments, ASM was used as a possible resistance inducer at a concentration of 0.001 g/L (dose label). Disease assessments for disease incidence and severity, biometric variables, and the quantification of oxidative stress were performed by determining the activity of the following antioxidant enzymes guaiacol peroxidase (GPOX) and superoxide dismutase (SOD), whereas malonaldehyde (MDA) and hydrogen peroxide (H2O2) contents were measured as an indication of the oxidative stress. Our results showed that the most effective method of ASM application against root rot and the decline in melon branches was seed treatment plus application in the aerial part of plants. Despite plants having one of the highest disease severity rates, after ASM application at this treatment, the pathogen was not capable to significantly affect plant growth and development. In addition, plants of this treatment presented one of the lowest MDA levels, which suggests a low lipid peroxidation. ASM seed treatment and aerial application also induced an increase in the activity of SOD and GPOX antioxidant enzymes, reducing the oxidative stress and improving plant resistance against melon root rot.