Physiological Responses Of Medicago Sativa L.to Waterlogging Stress

Alfalfa(Medicago sativa L.)is a perennial legume forage,which had been cultivated for two thousand years,it is the eralist and the most widely planted species in the word among the grazing forage.Alfalfa is known as "the king of forage"for its high yield,good quality,abundant nutrition.Alfalfa is suitable for warm and subarid climatic conditions,Our country's main producing area of alfalfa is in the north,the cultivation area of alfalfa in the south is comparatively small.In recent years,with the development of animal husbandry in South China,the demand for high quality forage becomes more and more.Accordingly,the alfalfa development has a great significance for the promotion of animal husbandry in South China.However,the high temperature and rainy climate make soil flooded easily,which seriously affect the normal growth and the development of alfalfa,greatly restricted the cultivation in the south.Thus,the alfalfa moisture resistance becomes the primary problem in alfalfa research in South China,and cultivation of alfalfa varieties which have tolerance to moisture is the key to the development of alfalfa in South China.In this research,the wet tolerance of different alfalfa varieties in geminating and seedling period has been studied to investigate the difference in humidity-resistant among alfalfa cultivars.In this experiment,the effects of Waterlogging stress on anaerobic respiratory enzyme activities and antioxidant enzyme activities in two alfalfa cultivars seedlings were studied for exploring mechanisms alfalfa evolved to adjust their cellular metabolism accordingly.The conclusion of this study are as follows:1.The wet tolerance of 14 alfalfa varieties in geminating and seedling period has been studied.The rusults showed that the germination rate,the root length,the bud height,the survival rate and the seedling height under wet stress decreased compared with control and significant differences existed among the 14 alfalfa varieties.The results of comprehensive evaluation indicated that there were significant differences among the 14 Medicago sativa L.varieties in the humidity-resistant,From the 14 Medicago sativa L.varieties,Yumu No.1 was selected as the most wet tolerance variety and Xinjiangziniquan was the most intolerance.2.Under waterlogging stress,the growth of alfalfa was inhibited,the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in the leaves and the activities of lactate dehydrogenase(LDH),pyruvate(PDC),alcohol dehydrogenase(ADH)in the roots increased significantly following the imposition of stress,which bear on the resistance of seedlings.The activity of LDH increased less,the activities of PDC and ADH of Yumu No.l increased much more than that of Xinjiangziniquan,which could increase the resistance of Yumu No.1 under waterlogging.3.The wet tolerance of alfalfa seedlings growing in the field were studied,the results showed that the plants were harmed under waterlogging stress.The stress induced leaf chlorosis and root rot,in the end the growth and survival rate declined.But alfalfa also formed a large number of lateral roots to adapt to the hypoxic enviroment.The growth and survival rate in Yumu No.l was much higher than that in Xinjiangziniquan,which indicated that Yumu No.l does have a strong humidity-resistant ability,the result is consistent with the germination stage and enzyme activity determination.