Physiological and biochemical responses of chilli pepper (Capsicum annuum L.) to sudden wilt syndrome

Abstract

Sudden wilt syndrome of chilli pepper is an emerging disorder characterized by unexpected and abrupt wilting of plants due to water stagnation and resultant hypoxic conditions in the rhizosphere. This problem is further exacerbated by infection of the soilborne fungus Fusarium oxysporum, which is not the primary cause. The study is an attempt to investigate physiological and biochemical alterations in three test organs (roots, leaves, and fruits) of chili pepper in response to sudden wilt syndrome. The sudden wilt-affected plants had lower levels of total phenols, o-dihydroxyphenols, flavonoids, ascorbic acid, Peroxidase, Polyphenol oxidase, Catalase, Phenylalanine ammonia lyase, Tyrosine ammonia lyase, Lignin, moisture content in leaves, Relative water content (RWC), Membrane stability Index (MSI), chlorophyll A and B and the gas exchange parameters (net photosynthesis, transpiration rate and stomatal conductance), all indicating an impaired defense system. On the contrary, there was a rise in the contents of hydrogen peroxide, malondialdehyde as well as proline, suggesting the onset of adaptive mechanisms that maintain normal osmoregulation in the stressed plants. The contents of total sugars and proteins were not affected in diseased plants compared to healthy plants. As the first systematic approach to understanding sudden chilli wilting, this study explains the biochemical and physiological changes that lead to this phenomenon.