Effect of 6-benzyladenine on soybean seed germination under salt stress and establishment of stress grade prediction model

Soil salinization severely hinders crop growth and decreases crop yield, and is increasingly an obstacle for the sustainability of agriculture. In this paper, different concentrations of NaCl (0, 50, 100, 150 mmol/L) and 6-benzyladenine (6-BA) (0, 1, 3, 5, 7 mg/L) were mixed together for investigating the mitigative effects of 6-BA on soybean (variety of Zhonghuang 13) germination stage under salt stress. Moreover, in order to quickly monitor the degree of salt stress on soybean, the low-field nuclear magnetic resonance (LF-NMR) technology was applied to assay the bonding water content and the dormancy of soybean seedling, and to establish the stress level prediction models of back propagation neural network (BPNN), resilient back propagation with backtracking neural network (RPROP-WBNN), resilient back propagation without backtracking neural network (RPROPOBNN), and global learning resilient back propagation neural network (GRPROPNN), and thus obtaining the optimal model. The results showed that (1) soybean exhibited strong bound water relaxation peaks under salt stress, thus enhancing their water storage capacity and overall survival; (2) the 6-BA could break the physiological dormancy of soybean seeds and promote germ elongation; (3) the RPROP-WBNN index values, including Precision (87.36 %), Recall (87.34 %), Accuracy (93.80 %), and F1-score (0.88) were outperformed the values of all other models. Overall, it could be concluded that the 3 mg/L 6-BA had the best effect on alleviating salt stress in soybean, and the RPROP-WBNN was more conducive to predicting accurately the salt stress level of soybean seeds with LF-NMR technology and neural network. Therefore, this paper could provide the theoretical support and data reference for the study of the response effects of 6-BA to salt stress during soybean seed germination stage with rapid non-destructive monitoring.