Evaluation of the resistance of alfalfa varieties to Aphis craccivora and correlation with plant nutrients

In this study, to clarify the differences in resistance to Aphis craccivora among different varieties of alfalfa and their correlation with plant nutritional constituents, we evaluated the resistance of alfalfa to A. craccivora based on the aphid ratio, and measured the contents of different nutritional constituents in alfalfa to determine the relationships between aphid resistance and these nutrients. The results revealed that different alfalfa varieties are characterized by differing levels of resistance to clover aphids. Specifically, ‘Algomquin’ was identified as a resistant variety with an aphid number ratio of 0.49, whereas ‘WL363’ ‘WL525’ ‘WL343’ ‘Western Star’, and ‘Zhongmu 1’ are moderately resistant varieties, with aphid number ratios of 0.68, 0.71, 0.72, 0.73, and 0.75, respectively, and ‘WL358’ and ‘Thunder’ are highly susceptible varieties, with respective aphid number ratios of 1.41 and 1.75. All other assessed varieties were found to be susceptible. In addition, we detected differences in nutrient contents among the different alfalfa varieties, with the aphid number ratio being significantly positively correlated with acid detergent fiber content (r = 0.544) and significantly negatively correlated with calcium (r = −0.653) and dry matter (r = −0.674) contents. Accordingly, the resistance of alfalfa to aphids was established to be negatively correlated with acid detergent fiber content and positively correlated with calcium and dry matter contents. Our findings in this study can provide a theoretical and practical basis for the prevention and control of aphids and the screening of aphid-resistant alfalfa varieties.