Chitosan nanoparticles mitigate Alternaria leaf spot disease of chilli in nitric oxide dependent way

The present study focuses on protection of emerging Alternaria leaf spot disease of chilli by application of chitosan nanoparticles (CNP). CNP was prepared by ionotropic gelation method and characterized. Antifungal potential of CNP was also checked against Alternaria alternata and its mechanisms were unraveled. Foliar application of CNP (0.001%) improved plant innate immunity in two chilli cultivars (one tolerant and one susceptible) by inducing the activities of different defense related enzymes along with total phenol and flavonoid. CNP application also induced callose deposition and reduced cell death in both the cultivar. Signaling molecule nitric oxide (NO) also augmented in CNP treated sets which were confirmed by both biochemical and microscopic data. In order to find out involvement of NO in CNP induced innate immunity in chilli cultivars, both NO surplus and NO depleted conditions were artificially created and defense responses were recorded. It was interesting to note that CNP mediated enhancement of defense responses in chilli plants was compromised in NO depleted condition. These results signify possible involvement of NO in CNP induced defense responses in chilli plants. It is evident from our results that CNP can be used to protect chilli plants against this fungal disease to develop a sustainable management strategy.