Large-scale integrated evaluation of salt tolerance in japonica rice at the germination stage

Background: Salt stress, one of the most important abiotic stresses, severely reduces crop yields. Identifying salt-tolerant rice germplasm resources at the germination stage, developing salt tolerance indicators, and cultivating salt-tolerant rice cultivars are crucial for improving rice production in saline soil.Results: We measured the germination parameters of 140 japonica rice cultivars on the 7 day after sowing (DAS) in 0 and 150 mmol L−1 NaCl. To accurately assess salt tolerance and identify reliable indicators of salt tolerance, we measured the shoot length (SL), root length (RL), root fresh weight (RFW), shoot fresh weight (SFW), total fresh weight (TFW) and salt tolerance (STI) index after 7 days of salt-stress treatment. The 140 rice cultivars were divided into four categories based on the mean MFVs: highly salt tolerant (HST: 19 cultivars), salt tolerant (ST: 74 cultivars), weakly salt tolerant (WST: 43 cultivars), and salt sensitive (SS: 4 cultivars). Based on the physiological indicators, we established a mathematical model to accurately evaluate salt tolerance in japonica rice cultivars. STI of TFW under 150 mmol L−1 NaCl treatment showed the highest correlation with salt tolerance during the germination stage.Conclusions: We determined the optimum NaCl concentration (150 mmol L−1) for evaluating salt tolerance in japonica rice at the germination stage. We identified 19 HST, 74 ST, 43 WST, and 4 SS japonica rice cultivars during the germination stage and proposed a mathematical model to evaluate salt tolerance. STI of TFW is a reliable, accurate indicator for evaluating salt tolerance in japonica rice. These findings should greatly facilitate the evaluation of japonica rice cultivars during seed germination and the breeding of salt-tolerant rice cultivars.