Exogenous N-acetylated chitooligosaccharides application improves osmotic stress and water deficit tolerance in Oryza sativa (cv. Swarna Sub-1) inducing seed germination, seedling growth, and biochemical activities

Rice (Oryza sativa L.) is an important food crop in India and this crop is sensitive to stress generated due to water-deficit/osmotic stress during germination and seedling growth ultimately showing detrimental effects on the growth & yield. In the present study, the effect of crude N-acetyl chitooligosaccharide (N-AcCOS) extract produced by microbial degradation of chitin was investigated on the germination performance of Swarna Sub-1 both under normal as well as osmotic stress conditions. Effects of exogenous application of N-AcCOS on the physiological and biochemical characteristics of rice were studied. The seeds were pre-soaked with three concentrations of N-AcCOS (0.2%, 0.5%, and 1%) at 25 °C temperature for 24 h. The results revealed that under stress conditions, germination percentage decreased for unsoaked seeds whereas for seeds presoaked in 1% (w/v) N-AcCOS solution showed a statistically significant improvement in the germination performance. In the case of optimal growth conditions, N-AcCOS presoaking resulted in the early emergence of radical and enhancement in other germination parameters like FGP, GI, DGP, and MGT. The microbially produced N-AcCOS, in its crude form, was applied to rice seedlings through foliar spraying under greenhouse conditions and was able to stabilize the membrane permeability, increased the chlorophyll content, and proline accumulation. The antioxidant enzyme levels like SOD, POD, and CAT was enhanced under the water-deficit stress after the foliar application of 300 mg/L of microbially produced N-AcCOS. Seed presoaking in N-AcCOS and exogenous application of N-AcCOS could be an efficient measure in mitigating the water-deficit stress in rice.