Enhancement of Growth, Photosynthetic Pigments, and Antioxidant Defense in Salt-Stressed Chilli (Capsicum annuum L.) by Chitosan

Abstract

Soil salinity is a critical abiotic factor that confines chilli (Capsicum annuum L.) growth and productivity by inducing oxidative damage and disrupting physiological and biochemical processes. This study investigated the effectiveness of exogenous chitosan in enhancing salinity tolerance in two chilli varieties, i.e., local variety Kajol and hybrid variety Dhanuya. Seedlings of both varieties were grown under four different conditions encompassing combinations of with and without salt stress (100 mM NaCl) and foliar application of chitosan (25 ppm). Salinity stress hindered plant height, branch and leaf counts, flower production, and photosynthetic pigments (chlorophyll a, chlorophyll b, and total chlorophyll) in both varieties. It also induced pronounced proline accumulation and boosted the activities of antioxidant enzymes catalase (CAT), peroxidase (POX), and ascorbate peroxidase (APX), reflecting enhanced oxidative stress. In contrast, foliar application of chitosan under saline conditions markedly alleviated the detrimental effects of salinity by improving growth attributes and preserving photosynthetic pigment levels. Supplementation of chitosan moderated proline accumulation and regulated antioxidant enzyme activities, thus sustaining cellular redox homeostasis under salt stress conditions. Chitosan application alone also promoted plant growth, improved photosynthetic pigment synthesis, and modulated antioxidant enzyme activities compared with the untreated control. These findings demonstrate that exogenous chitosan is an effective and environmentally friendly biostimulant for improving antioxidant defense responses, enhancing salinity tolerance, and sustaining chilli production in salt-affected environments.