Identification and application of salt-tolerant germplasms at germination stage in foxtail millet(Setaria italica L.)

In this study, 10 foxtail millet (Setaria italica L.) germplasm accessions were treated with varying concentrations of NaCl solution. By analyzing four indexes, including the relative germination potential, relative germination rate, relative shoot length, and relative root length during germination stage, we established that the suitable NaCl concentration for the identification of salt tolerance during germination in foxtail millet was 180 mmol/L. To evaluate the salt-tolerance of 180 core germplasms during the germination stage, correlation analysis and principal component analysis were employed to calculate the aforementioned four traits under 180 mmol/L NaCl treatment. Comprehensive evaluation and salt-tolerant grade of the 180 germplasms were identified by membership functional analysis and cluster analysis. Results revealed that except for the non-significant correlation between relative germination rate and relative shoot length, all other indexes showed a highly significant positive correlation. Furthermore, principal component analysis suggested that the four indexes could be considered as key indices for assessing salt tolerance. Cluster analysis revealed that the 180 germplasms could be divided into four groups: highly salt tolerant, salt tolerant, salt sensitive, and extremely salt sensitive. Jiangu, Henggu 12, Qitoubai, K-3606, and Jingu 20 were identified as extremely salt tolerant accessions through comprehensive evaluation using membership function. In addition, under 180 mmol/L NaCl stress, 40 lines from the F₇ generation recombinant inbred line (RIL) of Heizhigu (extremely salt-sensitive)×Changnong 35 (salt-tolerant) were analyzed. Results showed significant variation among the 40 lines, with their frequency distribution of salt tolerance grades approximating normal distribution, indicating that this population was suitable for salt-tolerant QTL mapping. These findings demonstrated that 180 mmol/L NaCl could be used for the identification of salt-tolerant foxtail millet germplasms during the germination stage and that at this concentration, salt tolerance differences among various germplasms can be better distinguished by four indexes: relative germination potential, relative germination rate, relative shoot length, and relative root length.