Effects Of Low Temperature Stress On Physiological Characteristics And Cold Resistance Of F₂ Alfalfa

Alfalfa?Medicago sativa L.?is a kind of forage grass which grows in the whole world.It has good palatability and high nutritional value,and it also becomes the most widely cultivated area in Northeast China,but the Northeast winter low temperature,freezing injury and death of alfalfa are often phenomenon,which makes North pasture production facing a big problem,so the breeding process in northern alfalfa varieties,cultivate excellent cold hardiness varieties is particularly important research work.The trait of cold hardiness is a quantitative trait controlled by multiple genes.Because of the difference of genetic background,there are obvious differences in the cold hardiness of alfalfa.In this study,Zhaodong alfalfa,WL323 and the 190 F₂ alfalfa populations obtained from the two crosses were used as experimental materials,in the field,the winter rate was investigated;24 h and 48 h were subjected to artificial low temperature stress and cold related physiological indexes were measured,in order to understand the effect of low temperature stress on physiological characteristics of alfalfa,understand the relationship between the indicators,understand the effects of various indexes on the cold resistance of alfalfa,provide a theoretical reference for the study on cold resistance of alfalfa,lay the foundation for the mapping of cold resistance related gene map and QTL mapping of related genes.The results of the study were as follows:1.Under low temperature stress,the activity of superoxide dismutase?SOD?and peroxidase?POD?activity of Zhaodong alfalfa and WL323 increased firstly and then decreased,and the increase rate of Zhaodong alfalfa was higher than WL323;The content of soluble sugar,the content of soluble protein and proline content showed increasing trend,and Zhaodong alfalfa was larger than WL323,showed a positive correlation with the cold resistant ability.2.The separation and distribution of cold resistance indexes of F₂ generation population were analyzed,it was found that all the indexes of F₂ generation group were obviously separated,and there were two ways;All the related indexes of cold resistance showed a continuous distribution,and the population was close to the normal distribution.3.The cluster analysis of 190 F₂ alfalfa populations by SPSS 21.0 showed that there was a great variation in F₂ generation.In the European genetic distance 4.78,F₂generation groups were classified into the following 4 categories,including 85individual plants,3 individual plants,1 individual plants,1 individual plants respectively;In the European genetic distance 3.58,F₂ generation groups were classified into the following 8 categories,large differences among groups.4.Using SPSS 21.0 to analyze the correlation between the overwintering rate of190 F₂ alfalfa populations and the related indexes of cold resistance,it is concluded that the indexes are not independent but interrelated.There was a significant positive correlation between the overwintering rate and SOD activity,POD activity and proline content in the F₂ generation,and was positively correlated with soluble sugar content and soluble protein content.5.The path analysis of the winter hardiness of 190 F₂ generation groups by using the correlation indexes of cold resistance of SPSS 21.0,in the direct path analysis,It was found that the effect of SOD activity on the overwintering rate of F₂ generation was mainly affected by the three factors,and the indirect effects of other physiological indexes were smaller,while the other four physiological indexes were affected by the direct and indirect effects on the overwintering rate of F₂ generation.