Assonciation Analysis Of Cold Resistance In Red Clover

Red clover(Trifolium pratense)is a perennial herb of the genus,which is widely distributed throughout the world.It is soft and rich in nutrients.which is a fine forage grass.Red clover prefers a warm and humid environment.The optimum temperature is between 15-25°C.More than 35°C or lower than 15°C,the red clover will stop growing.In the early spring and late autumn in northern China,low temperature or freezing often occurs,which seriously harms the growth of forage grass,which yield and quality also be affected.In this study,the natural population consisted of 72 red clover germplasm resources was used as the test material.The cold resistance of red clover was identified under low temperature 2.0°C stress,and 85 pairs of SSR loci were used for association analysis.we expect to provide cold-resistant molecular marker-assisted breeding and the development and utilization of cold-resistant germplasm resources of red clover with a basis theory.The main result of this paper are as follows:(1)The relative SOD,POD,CAT,MDA and soluble sugar(SS)at 7d,14 d and 21 d under low temperature 2.0 °C stressed,which indicated that the variation range of 5 relative physiological and biochemical indexes was relatively larged,and the relative CAT was largest at 21 d.The variation of relative SS was the largest at 7d,and the physiological and biochemical indexes presented normal distribution at 14 d and 21 d.(2)A total of 337 bands were amplified by scanning the genomic DNA of all 72 materials with 85 pairs of SSR molecular markers,which were 272 polymorphic bands,and the polymorphism ratio(PPB)was as high as 80.7%.The PIC value are all greater than 0.5,indicating that the selected SSR molecular markers have a higher level of polymorphism again,indicating a higher genetic diversity of the red clover population at the molecular level.(3)The population structure and linkage disequilibrium of the red clover natural population were analyzed using 85 pairs of SSR.The population structure analysis showed that the natural population was divided into two sub-populations,including 44 materials and 28 materials respectively;LD analysis showed that the distribution of linkage disequilibrium sites was more uniform.Most have a certain LD.(4)Association analysis to physiological and biochemical index related cold was carried out by using GLM and MLM models of TASSEL2.1 software.The results showed that under the low temperature stress,there are 15 SSR loci were associated significantly with red clover cold resistance.There were 31 significant associations(P≤0.01),which were 6 SSR molecular markers were significantly associated with two or more relative physiological and biochemical index.