Effects Of Exogenous Chitosan Application On Soybean Responses To Salinity Stress

Abstract

Salt stress is among the most destructive factors behind the inhibition of plant growth and physiological activities. The chitosan biopolymer is a de-acetylated derivative of chitin that can be extracted from shrimp peels. Chitosan, particularly oligochitosan is rising as a bio-stimulant that can enhance salinity tolerance. This study investigated the impact of oligochitosan foliar spray with five different concentrations (0, 100, 200, 300, and 400 ppm) in a 7-day interval on soybean (local cultivar DT84) responses to salinity stress (0, 50, 100, 150 mM levels of NaCl), and elucidated their interaction. The highest salinity stress (150 mM NaCl) curbed root fresh weight, shoot fresh weight and root-to-shoot dry weight ratio by 61%, 36%, and 33%, respectively. The leaf scorch score also increased by 39%, while the results showed little change in relative water content, root length and shoot length. Oligochitosan foliar spray at 100 and 200 ppm moderated the above negative effects of salinity stress, with 200ppm being the optimal concentration. The moderating effects of oligochitosan administration at 200ppm were most pronounced under 100 mM NaCl stress. Specifically, compared to the non-supplemented stressed plants, foliar oligochitosan spray at 200 ppm ameliorated leaf scorch score by 28%, improved root fresh weight and shoot fresh weight by 79% and 32%, respectively. Root-to-shoot ratio also increased by 24%, suggesting that the improvement in root biomass played an important role in oligochitosan-induced salt tolerance. There was an interaction between oligochitosan application and salinity stress on leaf scorch score, shoot length, root weight, and root-to-shoot dry weight ratio. In summary, the results showed that for soybeans, foliar spray of oligochitosan at 200 ppm played a positive role in diminishing harmful damages caused by NaCl stress, thus enhancing the salinity tolerance of soybean. This was mainly achieved by the maintenance of normal growth in both shoot and root and the augmentation of the root system possibly via the improved development of lateral roots.