A Comprehensive Evaluation Of Alfalfa (Medicago Sativa) Varieties For Drought Tolerance

A comprehensive evaluation of alfalfa (Medicago sativa) varieties for drought toleranceEight alfalfa (Medicago sativa) varieties were selected from 62 varieties based on a similar density under field drought conditions. Two field production parameters of hay yield and regrowth rate after cuttings were measured during 2002a to 2003a. Vitro leaves at artificial drought stress were subjected to 6 physiological indices test in laboratory which included relative water content,membrane permeability,proline content,chlorophyll content,activities of catalase and superoxide dismutase. Capacity of drought tolerance of test varieties was comprehensively evaluated based on the above parameters and indices. The mian results obtained are as following:There was significantly different in hay yield of each cutting, total yield of 5 cuttings and average regrowth rate over 5 cuttings among the test varieties. Two variety groups can be divided according to total hay yield, variety Prime,Gongnong No.2 and Longdong were performed better than the others. The test varieties can alsp be separated into two groups based on the average regrowth rate in which variety L173 was the fastest in growth. The hay yield differed with alfalfa ages and cuttings, the hay yield of two-year old plants was less than that of three-year old, the hay yield of the first cutting in each age group was higher than that of subsequent cuttings, the average hay yield of two-year old plants was 268.98 g/m2 that accounted for 54.3% of the two-year old plants' total hay yield. That of three-year old was 666.68g/m2, which accounted for 62.1%.The results of six physiological indices measured by vitro leaves at different drought treatment period from 0~72h indicated that all varieties tested showed similar tendency: as the drought period increased, there was graduatedly decreased in relative water content,chlorophyll content, activities of catalase and superoxide dismutase; but increased with the membrane permeability and proline accumulation. Furthermor, the capacity of drought tolerance of test varities could be separated into certain groups based on each of the physiological indices. Results of relationship between hay yield and other parameters and indices used showed that the hay yield was siginficantly positive correlated with plant regrowth rate (r=0.7487, p<0.01), leaf Proline accumulation (r=0.4702, p<0.01) and water maitenance ability (r=0.4044, p<0.05). The other physiological indices were not siginficantly related to the hay yield.A cluster analysis was done on the eight varieties using 8 parameters and indices. The varieties were seperated into four groups based on their drought tolerance: best, good, middle, poor. The best varieties for drought tolerance were cultivars Prime and Gongnong No.2. Cultivars Shanbei and L173 were good, Dingxi and longdong middle, While Hexi and Algonguin were poor.