Comparative evaluation of biochemical changes associated with green gram varieties against anthracnose disease

Twenty-five varieties of green gram were evaluated under field conditions over three consecutive Kharif seasons (June-September) in 2019, 2020, and 2021 to determine their response to anthracnose disease. Varietal screening was done using the standard percent disease index (0-9) scale, revealing a mean percent disease index ranging from ≥3 to ≤66 percent (p < 0.05). Notably, two varieties TARM 18 and AKM8823 demonstrated resistance to anthracnose, with mean percent disease indices of 3.93 and 4.08 percent, respectively, though none were found to be immune. One representative variety from each category, i.e., resistant (TARM18), moderately resistant (NKM1512), moderately susceptible (RMG62), susceptible (CoGG912) and highly susceptible (K851) were selected for further biochemical analysis with PDI of 3.93, 8.73, 14.9, 27.72 and 64.77, respectively. Biochemical analyses of healthy and anthracnose infected leaves of TARM18 revealed (19.95, 32.11 and 24.73 %) elevated level of phenol, free amino acids and protein content, respectively as compared to their healthy counterparts. Similarly, enzymatic activity analysis indicated that the infected leaves exhibited (17.98, 22.55 and 22.68 %) higher levels of polyphenol oxidase, peroxidase and super oxide dismutase activity compared to healthy leaves. In contrast, the highly susceptible variety K-851 demonstrated slight increase (9.95, 15.38 and 12.09 %) in phenol, free amino acids and protein content, respectively. Similar trend was observed in case of enzymatic activity showing reduced levels (13.33, 11.39 and 6.99 %) of polyphenol oxidase, peroxidase and super oxide dismutase, respectively. These results also showed highest pearson correlation coefficient between PDI and phenols (r = -0.929) followed by proteins (r = -0.903). These results demonstrate that the increased levels of phenols and proteins contributed to the activation of defense responses, leading to enhanced disease resistance in TARM-18 compared to K-851 (p < 0.05). This suggests their potential use as biochemical markers in future resistance breeding programs.