Chitosan Induces Water Deficit Stress Tolerance in Gladiolus grandiflorus via Regulating Water Relations, Gaseous Exchange Traits, and Antioxidative Defense

Abstract

Water deficit stress (WDS) causes massive losses in cut flower production. Various sustainable protectants are reported to improve the WDS tolerance in ornamentals. The physio-chemical and ornamental aspects in response to foliarly applied chitosan (Ci) for the amelioration of WDS induced oxidative stress in geophyte cut flowers still need to be explored. Hence, in this study, the effect of foliar application of Ci was tested on the said attributes of Gladiolus under WDS conditions. Initially, different levels of Ci were foliarly applied on potted Gladiolus plants under normal (100% field capacity (FC)) and WDS (60% FC). The study comprised two experiments: optimization of Ci dose (0, 2.5, 5, 7.5, and 10 mg L-1) (Experiment 1) and assessing the impact of optimized dose of Ci (7.5 mg L-1) (Experiment 2) on the physiological, biochemical, and flowering responses of Gladiolus plants under WDS. Ci significantly increased the leaf area (17%), shoot length (31%), relative fresh weight (12%), and shoot dry weight (27%) under WDS than normal irrigated plants. Moreover, Ci application under WDS induced a considerable increase related to the photosynthetic rate (46%), transpiration rate (53%), substomatal conductance (9%), water use efficiency (53%), chlorophyll a (60%), chlorophyll b (32%) and carotenoids (65%) compared to control. Further, Ci (7.5 mg L-1) foliar supplementation under WDS contributed to improve oxidative defense by enhancing the activities of catalase (5%), peroxidase (30%), and superoxide dismutase (29%) while decreasing the malondialdehyde (31%) and hydrogen peroxide (33%) compared to control. The number of open florets and number of corms were improved by 50% and 43% respectively, in Ci treated water deficit stressed plants. Ci was found to be effective in regulating water relations, gaseous exchange, and metabolic activities for improving the growth and flowering of Gladiolus.