An evaluation of the resistance of alfalfa cultivars to Stemphyliumand Phoma leaf spot diseases

Forty alfalfa(Medicago sativa)cultivars were collected from China and abroad and inoculated with suspensions of different concentrations of spores fromStemphyliumleaf spot and Phomaleaf spot diseases to evaluate the resistance of alfalfa to these two leaf spot diseases and identify the optimal inoculation concentration.The disease indices of 10 cultivars inoculated with these two fungi gradually increased with concentration increase of the spore suspensions.The appropriate inoculation concentrations for comparing cultivar resistance to Stemphyliumand Phoma were 1×105 to 1×106 spores per milliliter and 1×106 spores per milliliter,respectively.With a concentration of 1×106 spores per milliliter in the inoculate,the disease indices of Stemphylium leaf spot in forty cultivars ranged from 3.33 to 35.83,while the disease indices of Phomaleaf spot ranged from13.07 to 52.27.There were significant differences between the 40cultivars(P0.05).Fourteen cultivars were found to be resistant to Stemphyliumleaf spot,including one highly-resistant cultivar-Gongnong No.2and thirteen moderately-resistant cultivars.Only one cultivar,Rambler,from America was found to have moderate resistance to Phomaleaf spot.