Exploring the role of elevated antioxidants and antioxidant enzymes in conferring resistance against Alternaria porri in onion germplasm

The antioxidants and defense associated antioxidant enzymes associated with the entry of foreign bodies signal the first line of defense. In the present study, onion germplasm was analyzed for various biochemical parameters in response to inoculation Alternaria. porri for establishing role of antioxidant defense mechanism in onion for understanding their role in antioxidant-associated defense mechanism. The genotypes were categorized as resistant, moderately susceptible, susceptible and highly susceptible based on percent disease index (PDI). There were significant differences for all the parameters studied before and after inoculation. As compared to resistant genotypes, the susceptible and highly susceptible genotypes showed minimum total chlorophyll content at 3 weeks post-inoculation. The total phenol content in the leaf of resistant genotypes was high (246.4 mg GAE/100g FW) as compared to moderate susceptible (115.99 mg GAE/100g FW), susceptible (151.14 mg GAE/100g FW) and highly susceptible (146.60 mg GAE/100g FW) genotypes at 3 weeks post-inoculation (WPI). The antioxidant enzymes namely catalase, peroxidase and superoxide dismutase production increased upto 3 WPI. The activity of antioxidant enzymes (catalase, peroxidase and superoxide dismutase) was significantly high in resistant genotypes (9.80, 12.80 & 9.39 µmole/min/mg protein, respectively) as compared to moderately susceptible, susceptible and highly susceptible genotypes at 3 WPI. The study supports that antioxidant enzymes play a significant role in defense mechanism in conferring resistance against purple blotch and can be used as an effective bio-marker in resistance breeding against Alternaria porri .