To explore the ideal traits and methods that can characterize the drought resistance of the core germplasm population of alfalfa at the seedling stage, and to mine excellent drought-resistant germplasm, so as to provide technical support and material basis for the identification of drought resistance of alfalfa at the seedling stage, germplasm innovation and breeding.

Using 111 core germplasms of alfalfa as materials, the single drought resistance coefficients of six traits, namely plant height (PH), shoot fresh weight (SFW), shoot dry weight (SDW), main root length (MRL), root fresh weight (RFW), and root dry weight (RDW), were determined under natural drought stress and normal water supply (control). Combining the analysis methods such as the single drought resistance coefficient, correlation, principal component, membership function, linear stepwise regression, and clustering of each trait of alfalfa, the response differences of each alfalfa germplasm to drought stress were evaluated, the traits and methods for identifying drought resistance at the seedling stage were screened, and the excellent resources of drought resistance at the seedling stage of alfalfa were explored.

The analysis of the single drought resistance coefficient indicated that drought stress significantly inhibited all six traits of alfalfa at the seedling stage. The results of trait correlation showed that there was a positive correlation among the six traits. The principal component results indicated that the six individual drought-resistant traits of alfalfa could be combined into four comprehensive drought-resistant traits, and the cumulative contribution rate reached 86.885%. The methods such as single drought resistance coefficient, correlation, principal component and linear stepwise regression were comprehensively evaluated to determine that SFW, SDW, RFW and RDW were the ideal traits for evaluating alfalfa materials at the seedling stage. Using the classification methods of CDC value and D value, the drought resistance of 111 core germplasm populations of alfalfa at the seedling stage was classified. It was found that there were only subtle differences in the classification of drought resistance of various germplasm by the two drought resistance classification methods. The D values of 111 alfalfa core germplasms were clustered and classified. The various germplasms were divided into 5 categories, which belonged to strongly drought-resistant, moderately drought-resistant, moderately drought-resistant and drought-sensitive germplasms respectively.

Determine that SFW, SDW, RFW and RDW are the best traits for drought resistance evaluation of alfalfa at the seedling stage; The number of highly drought-resistant and relatively drought-resistant materials of alfalfa at the seedling stage excavated was 6 and 25 respectively.