Evaluation of physiological and biochemical response of alfalfa cultivars during summer

High temperature induces a series of responses in physiology and morphology. In order to study this changes, 22 alfalfa (Medicago sativa) varieties were used to measure the contents of relative water content, soluble protein, relative electrical conductivity, and the activity of superoxide dismutase and peroxidase under different natural temperature in the summer. A randomized complete block design was conducted with three replicates. Using the method of cluster analysis, the heat resistance of these varieties were preliminarily evaluated. The results showed that, 1) the four indicators except the relative electrical conductivity, increased as the temperature progressed from 25 May to 21 June, and then dropped as the temperature dropped. However, the relative electrical conductivity increased by 3.36 times gradually; 2) in this study, 22 alfalfa varieties were divided into three types by hierarchical clustering, which are strong heatresistance type, weak heatresistance varieties and intermediate type, respectively. The varieties of heatresistant type included Sitel, followed Derby, Phabulous, Empress 2000, 8925MF, Gold Empress and WL414, while the intermediate heatresistant varieties were Sardi 7, Alfasuper, Powerplant, WL525HQ, Algonquin, Hunter River, Alfking, AmeriGraze401 and Siriver. The other varieties were weak heatresistant varieties; 3) there was very significant negatively correlation (P0.01) between FD class and relative water content. There were significant negatively correlations (P0.05) between FD class and soluble protein content, and FD class and POD activity. The relationships between FD class and the conductivity or FD class and SOD activity were not significant (P0.05). The correlation coefficient were 0.138 and -0.405. There were significant correlations among different indicators (P0.01).