Evaluation of Promising Characteristics of Rhizomatous Alfalfa Male Sterile Mutant Accessions

Evaluating key traits of male sterile mutant accessions in rhizomatous alfalfa (Medicago sativa L.) is crucial for selecting plants for artificial hybrid breeding of rhizomatous maternal lines. In this study, branch cuttings from four male sterile mutant accessions of ‘Qingshui’ alfalfa were used as experimental samples. We evaluated phenotypic traits, which included pollen viability and stigma receptivity, as well as nutritional quality, using difference analysis, correlation analysis, and principal component analysis. Prioritizing pollen viability and stigma receptivity, while considering phenotypic traits and nutritional quality as supplementary factors, allowed us to comprehensively evaluate 24 rhizomatous alfalfa individuals. This evaluation led to the identification of four male sterile mutant accessions with superior traits. The pollen from accession 4-4 was found to be partially fertile, whereas the remaining 23 alfalfa individuals were entirely male sterile. All 24 individuals exhibited stigma receptivity levels suitable for effective pollination. Principal component analysis revealed that among the assessed traits, the leaf–stem ratio contributed most significantly, followed by crude protein content, while neutral detergent fiber content had the least impact on overall quality. Additionally, the number of branches showed a strong positive correlation with individual plant yield (p < 0.01). No significant correlations were detected among plant height, stem diameter, forage grading index, crude protein, neutral detergent fiber, acid detergent fiber content, and yield. Overall, our comprehensive evaluation suggests that accessions 1-2, 2-2, 3-1, and 4-3 are most suitable for use as parental lines in artificial hybrid breeding.