Defence Inducers Upregulate Metabolic and Antioxidant Activity to Suppress Charcoal Rot Disease in Mung Bean (Vigna radiata L.)

The biochemical responses of two mung bean (Vigna radiata L.) cultivars to charcoal rot disease, caused by the fungal pathogen Macrophomina phaseolina, were investigated under controlled greenhouse conditions. The cultivars were Bireshwar (WBM 4-34-1-1), which is resistant to the disease, and Samrat (PDM-139), which is susceptible. The greenhouse environment was maintained at a temperature of 24°C ± 2°C and a relative humidity of 85%–90%. These cultivars were initially identified for their varying resistance levels through field screening. Seeds were treated with four distinct defence-inducing compounds: salicylic acid (SA), chitosan, yeast extract and jasmonic acid (JA). These elicitors were applied at three concentrations: SA (0.5, 1, 2 mM), chitosan (0.01, 0.03, 0.07 mM), yeast extract (0.02%, 0.05%, 0.1%) and JA (0.02%, 0.05%, 0.1%). The treated plants exhibited a notable and statistically significant enhancement in the accumulation of several defence-related biochemical markers, including catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), ortho-dihydroxy phenols (OD phenols), total phenols and ascorbic acid, when compared to the untreated control group. SA at higher concentrations was most effective, followed by chitosan and JA, in enhancing these biochemical defences. Following pathogen inoculation, elevated levels of CAT, PAL, POD, PPO, OD phenols and total phenols were associated with reduced disease severity. Correlation analysis revealed a strong negative relationship between Percent Disease Index (PDI) and most biochemical variables, especially at 20 days after sowing (DAS), except for PPO and ascorbic acid. These findings underscore the critical role of biochemical defence mechanisms in conferring resistance to charcoal rot disease. The study suggests that high levels of biochemical activity during the early stages of plant development could be used as a valuable selection criterion in breeding programmes aimed at enhancing disease resistance.