Abstract: 【Objective】The aim of this study was to identify simple sequence repeat (SSR) loci associated with fall dormancy in alfalfa (Medicago sativa L.) for understanding its inheritance pattern and molecular mechanism.【Method】The association population was composed of a total of 321 tetraploid genotypes from 75 alfalfa accessions, and each of the Chinese accessions was represented by six to eight genotypes, while the remaining ones included three to four genotypes. All the 321 materials were genotyped using 85 SSR markers randomly distributed on alfalfa genome. The phenotyping data of fall dormancy trait of these alfalfa accessions was obtained in 2014 and 2015, and used together with the SSR genotyping results for an association mapping by using General Line Model (GLM) and Mixed Line Model (MLM) models.【Result】It was showed that the fall dormancy trait in alfalfa was significantly influenced by genotypes, years, and genotype × year interactions. The fall plant heights ranged between 5.1 cm and 55.1 cm, and between 3.5 cm and 44.9 cm, averages of 22.4 cm and 15.2 cm, and coefficients of variation at 45.5% and 43.7% in 2014 and 2015, respectively. This trait showed a normal or nearly normal distribution in both 2014 and 2015 and had a relatively high broad-sense heritability at 0.71. The MLM model which adequately controlled false positives identified a total of 12 and 11 significant associations accounting for 2.42% to 6.73% and 2.45% to 4.81% of the phenotypic variances in 2014 and 2015, respectively. Among them, four loci of m83_157 on Chr. 2, m525_230 and m525_231 on Chr. 3, and m429_245 on Chr. 4 were detected in the two years by using the two models.【Conclusion】It was concluded that the four association loci related to fall dormancy in alfalfa were identified, and would be subjected to functional verification so that they could be eventually used for alfalfa marker assisted selection breeding.

Key words: alfalfa, association mapping, SSR marker, fall dormancy