A Biopolymer Laminarin Elicits Antioxidant Defense in Different Cultivars of Solanum Lycopersicum Against Early Blight Disease Caused by Alternaria Solani

ABSTRACT The study evaluates the potential of laminarin (LaM), a biopolymer, in inducing antioxidative defense in tomato against early blight disease caused by Alternaria solani . Histological analysis of A. solani infection in susceptible (PKM-1) and tolerant (Arka Rakshak) cultivars of tomato showed increased pathogen colonization in PKM-1 by day 8 compared to Arka Rakshak. Fluorescent microscopic analysis with a chitin-specific dye, Calcofluor white, demonstrated reduced A. solani colonization in PKM-1 pretreated with LaM (0.1%), followed by A. solani infection on par with Arka Rakshak. A significant increase in the accumulation of hydrogen peroxide was observed in LaM-pretreated leaves (0.050%, 0.075% and 0.1%) at 24- and 48-hours post-infection in both cultivars. A quantitative increase in guaiacol peroxidase (GPX) activity was recorded in LaM (0.025%), followed by A. solani infection leaves at 36 hrs in Arka Rakshak, whereas LaM (0.010%) followed by A. solani infection recorded maximum GPX activity at 24 hrs in PKM-1. Induction of new GPX isoform was evident in LaM (0.075% and 0.1%) pretreated, and LaM pretreated, followed by A. solani infected leaves of both cultivars at 24 hrs. There was a significant reduction in disease severity in tomato leaves pretreated with LaM (0.1%) and infected with A. solani . The results suggest that LaM could be a potential elicitor of antioxidant defense in tomato against A. solani infection, which can further be harnessed to develop sustainable strategies for managing early blight disease while reducing dependence on chemical fungicides.