Abstract: The objective of this study was to compare the resistance of different alfalfa varieties to virus disease. Virus loads of 30 alfalfa varieties were investigated in plants in the field. The virus species present in the alfalfa plants were detected and identified using small RNA high-throughput sequencing and RT-PCR technology. Data collected for the 30 alfalfa varieties included the virus incidence rate, disease index, relative plant height, relative dry weight per plant, relative stem diameter, relative leaf area, relative leaf length and relative leaf width, and these data were used to comprehensively compare the disease resistance of the 30 tested varieties. Cluster analysis of some traits was also carried out. Among the 30 tested alfalfa varieties, only alfalfa mosaic virus (AMV) infection was detected. The field incidence of AMV in all alfalfa varieties was more than 94%, and the values of the multivariate disease index ranged from 31.53 to 55.50. There was 1 resistant variety (Sheshou No.2); there were 6 partially resistant varieties, and 23 susceptible varieties. The cluster analysis indicated that Sheshou No.2 had an AMV resistance profile far different from all other alfalfa varieties, as indicated by the measured traits. It can be speculated that hybridization of other varieties with Sheshou No. 2 would produce high heterosis.

Key words: alfalfa variety, virus disease, resistance, cluster analysis