Identification and Evaluation of Drought Resistance for 111 Germplasm Resources of Alfalfa During Germination Stage

To identify and evaluate the drought resistance of alfalfa germplasm resources, screen out different drought-resistant alfalfa germplasm materials, and lay a foundation for further development of drought-resistant alfalfa resources creation and breeding utilization.

In this study, A total of 111 alfalfa germplasm resources were used as experimental materials, and drought stress conditions were simulated using a 13% PEG-6000 solution. Two treatments were established: drought stress (13% PEG-6000) and a control (distilled water). Drought tolerance at germination stage were comprehensively evaluated by the comprehensive drought resistance coefficient (CDC value) and drought resistance coefficient (D value) using nine indicators, including germination potential, germination rate, germination index, vitality index, promptness index, root length, bud length, fresh weight and dry weight. Meanwhile, single drought tolerance coefficients, correlation analysis, principal component analysis and stepwise regression analysis were conducted to identify the key indicators influencing drought resistance during germination.

Analysis of the single drought tolerance coefficients for the nine indicators showed that vitality index, fresh weight, and promptness index were key indicators for screening drought resistance at the germination stage. The single drought tolerance coefficients of the indicators had the highest correlation among germination index and promptness index, germination rate, vitality index, with coefficients of 0.9838, 0.9495 and 0.9338, respectively. Principal component analysis transformed the nine indicators into three principal components with a cumulative contribution of 87.287%. Drought resistance of alfalfa at germination stage was identified using two methods with CDC value and D value, and it was found that the evaluation results of the two methods were highly consistent; however, the D value method was more comprehensive, reliable, and accurate, as it used the weighting coefficients to reflect the degree of influence of each indicator to the overall drought resistance of the varieties. Based on the D value, the 111 alfalfa germplasm resources were clustered into five categories: ClassⅠ(strongest drought resistance, 1 accession), Class Ⅱ (strong drought resistance, 5 accessions), Class Ⅲ (moderate drought resistance, 55 accessions), Class Ⅳ (weak drought resistance, 37 accessions), and Class Ⅴ (drought-sensitive, 13 accessions).

The D value evaluation method was found to be the most reliable for assessing drought resistance in alfalfa during the germination stage; The study identified AG37 as the strongest drought resistance germplasm, along with five strong drought resistance accessions, including AG19, AG5, AG13 and other. Vitality index and promptness index were determined to be the most suitable indicators for evaluating drought resistance in alfalfa at the germination stage.