Abstract: Anthracnose caused by Colletotrichum americae-borealis is a serious disease of alfalfa (Medicago sativa), which has been widespread in Inner Mongolia in recent years. This study evaluated the resistance of 44 alfalfa varieties to anthracnose in the Shaerqin area of Inner Mongolia, in order to determine the anthracnose effect on alfalfa yield and quality. We also evaluated the disease severity in three alfalfa varieties: Hunter river, Magnum 2 and Reindeer. Yield loss assessments were performed to evaluate the effects of anthracnose on nutritional content and amino acid content in the variety reindeer. The results showed that there were differences in resistance to anthracnose among the 44 tested alfalfa varieties. The tested varieties were classified as having high susceptibility (13 varieties), moderate susceptibility (14 varieties), moderate resistance (13 varieties), or high resistance (1 variety). Hunter river, Reindeer, and Magnum 2 were among the highly susceptible varieties and should not be grown in this area. Compared with healthy plants, the plant dry weight of severely affected Hunter river, Magnum 2 and Reindeer varieties was reduced by 6.72%-27.24% (P<0.05), and yield was significantly reduced by 6.795-37.39% (P<0.05). Compared with lightly diseased plants, the yields of severely susceptible Reindeer, Magnum 2 and Hunter river decreased significantly by 0.49% to 21.06% (P<0.05). The contents of neutral detergent fiber and acid detergent fiber were, respectively, 20.57% and 15.79% higher in severely diseased plants than in healthy plants (P<0.05), while other indicators such as crude fat and crude protein were significantly lower (34.53% and 16.52%, respectively) than those in healthy plants (P<0.05). Anthracnose reduced the amino acid contents of the tested alfalfa varieties (P<0.05). For example, methionine, isoleucine, lysine, cysteine and histidine contents were reduced by 54.21%-85.88%. A regression equation was established with anthracnose severity as the independent variable and values of the various quality indexes as the dependent variables. Crude fat, neutral detergent fiber, threonine, leucine, alanine, and tyrosine showed a significant negative correlation and a good fit. In summary, when anthracnose is severe, the disease not only significantly reduces the yield, but also affects crop nutritive quality. Therefore, anthracnose should be controlled.

Key words: alfalfa, anthracnose, resistance, yield, quality