Identification and evaluation of saline-alkali tolerance at germination stage and elite germplasm screening of Taraxacum kok-saghyz Rodin

【Objective】 This study aimed to evaluate the saline-alkali tolerance of Taraxacum kok-saghyz Rodin germplasm resources at germination stage， and establish an evaluation system of saline-alkali tolerance，so as to provide theoretical references for screening saline-alkali tolerance genes and breeding saline-alkali tolerant cultivars. 【Method】 Thirty-six germplasm resources of Taraxacum kok-saghyz Rodin were as materials， and a solution with NaCl∶Na₂SO₄∶NaHCO₃=3∶1∶1 （molar ratio） was used to simulate saline-alkali tolerance. Six mixed saline-alkali concentration gradients were set at 0， 50， 100， 150， 200， and 250 mmol/L. The germination potential and germination rate of three Taraxacum kok-saghyz Rodin germplasms （K445， TK30， and TK37） were analyzed to screen the optimal tolerance concentration for identifying and evaluating saline-alkali tolerance at germination stage. Under the screened optimal tolerance concentration， a saline-alkali tolerance experiment was conducted on 36 Taraxacum kok-saghyz Rodin germplasms at germination stage， with distilled water treatment as the control group （CK）. Based on trait ratios related to saline-alkali tolerance such as relative germination potential， relative germination rate， relative germination index， damage rate， relative bud length， and relative root length， correlation analysis， principal component analysis， comprehensive evaluation， and cluster analysis were performed. 【Result】 Under conditions of different concentrations of saline-alkali stress， the germination potential and germination rate of K445， TK30， and TK37 all decreased as the concentration of mixed saline-alkali solution increased. At the stress concentration reached 150 mmol/L， the tested Taraxacum kok-saghyz Rodin exhibited rich genetic variation， so 150 mmol/L was identified as the suitable concentration for evaluating the saline-alkali tolerance. Under stress treatment with 150 mmol/L saline-alkali solution， the germination potential， germination rate， germination index， bud length， and root length of the treatment group were all lower than those of CK. The coefficients of variation for the six saline-alkali tolerance-related traits ranged from 6.64% to 54.37%， ranked as relative root length<relative bud length<damage rate<relative germination index<relative germination rate<relative germination potential. Relative germination potential showed an extremely significant positive correlation （P<0.01， the same below） with both relative germination rate and relative germination index， and an extremely significant negative correlation with the damage rate. Relative germination rate showed an extremely significant positive correlation with relative germination index， and showed an extremely significant negative correlation with the damage rate. Relative germination index showed an extremely significant negative correlation with the damage rate. Relative bud length showed a significant positive correlation with relative root length （P<0.05）. The cumulative contribution rate of the two principal components transformed from the six indexes reached 84.276%. The 36 Taraxacum kok-saghyz Rodin germplasms could be classified into four clusters： one was identified as highly saline-alkali tolerant germplasm， 15 as moderately saline-alkali tolerant germplasms， 13 as saline-alkali tolerant germplasms， and seven as saline-alkali sensitive germplasms. Based on the D value， a regression equation for the identification and evaluation of saline-alkali tolerance was established： D=-0.527+0.236X₁+0.758X₂+0.412X₃+0.493X₄+0.224X₅-0.244X₆. This regression equation demonstrated a good fit and could be used for the identification and evaluation of saline-alkali tolerance of Taraxacum kok-saghyz Rodin germplasm resources. 【Conclusion】 The optimal saline-alkali stress concentration for evaluating salt-alkali tolerance of Taraxacum kok-saghyz Rodin at germination stage is 150 mmol/L. This concentration inhibits six traits related to saline-alkali tolerance measured at germination stage. Among the 36 Taraxacum kok-saghyz Rodin germplasms， one highly saline-alkali tolerant germplasm and seven saline-alkali sensitive germplasms are identified. The six traits related to saline-alkali tolerance （relative germination rate， relative bud length， relative root length， relative germination index， relative germination potential， and damage rate） could serve as effective indexes for identif-ying and evaluating saline-alkali tolerance of Taraxacum kok-saghyz Rodin germplasms at germination stage.