Evaluation Of Biological Nitrogen Fixation Traits Of Melilotus Albus Half-sib Families

Melilotus albus is a legume herb,which has a strong resistance to adversity and barren,can nodulate and fix nitrogen,and has potential feeding value.However,there is little evaluation of nitrogen fixation ability in the cultivation and breeding of Melilotus albus in China.Because of this,to verify the feasibility of genetic improvement of Melilotus albus nitrogen fixation ability in breeding,and to provide a theoretical basis for the cultivation of high-quality forage and the evaluation of nitrogen fixation ability.Twenty-six half-sib families of Melilotus albus in breeding were used as experimental materials to carry out field experiments to explore the nitrogen fixation ability of Melilotus albus in the field and the nitrogen fixation characters with genetic improvement value.Greenhouse experiments were carried out to explore the effects of different indigenous Rhizobia on the nitrogen fixation capacity of Melilotus albus.（1）Field trials in two locations of Yuzhong and Linze showed that the location,half-sib families,and the interaction of these two factors had a significant effect on the root dry weight,nodule number,nodule weight,leaf total nitrogen and leaf total phosphorus of Melilotus albus（P<0.01）.After doing the principal component analysis,the half-sib families were divided into four groups.A Melilotus albus group with the best performance of the above indexes was 4%,26%,10%,17%,21%,and 11%higher than the control.The B value of Melilotus albus is-1.67‰.The maximum and minimum values of biological nitrogen fixation percentage（%Ndfa）were 58%and43%,respectively.In Linze and Yuzhong areas,the variance of genotypes was significant（P<0.05）,and the indexes were nodule number and leaf total nitrogen.The genetic gains were 23.94%and 7.97%,respectively.The significant correlation（P<0.01）was found in Leaf total nitrogen and nodule number,leaf total phosphorus,and dry weight of roots.（2）In the greenhouse,four families were inoculated with indigenous rhizobia from three areas and their nitrogen fixation ability was measured.The results showed that the total nitrogen accumulation of Melilotus albus was similar to that of the comprehensive evaluation index,and the family Ma-HSF₂-1 ranked the highest.The stepwise regression model based on the D value of comprehensive evaluation,R²=0.997.The top three indexes with the highest correlation degree with D value were root dry weight,root phosphorus accumulation,and root nitrogen accumulation.Except that the main root length and the first lateral root length were weakly negatively correlated with nitrogen accumulation,the other indexes were positively correlated with nitrogen accumulation.The order of root,stem,and leaf dry weight was root>leaf>stem.The stem total nitrogen content and the ratio of nitrogen to phosphorus were the lowest.Except that the stem nitrogen content of Ma-HSF₂-1 was lower than that of alfalfa,the leaf stem root dry weight,total nitrogen,total phosphorus,nitrogen accumulation,and phosphorus accumulation of Ma-HSF₂-1 were higher than that of alfalfa.The ratio of dry weight,total nitrogen,total phosphorus,nitrogen accumulation,and phosphorus accumulation index to organs of Ma-HSF₂-1 was higher than that of alfalfa.The highest expression of the nifH gene was found in Ma-HSF₂-1 and the lowest in Ma-HSF₂-18.There were many rhizobia in Ma-HSF₂-1 and Ma-HSF₂-18 nodules,and the dominant rhizobia are Sinorhizobium.Compared with Ma-HSF₂-18,the other rhizobia,Rubrivivax,Mesorhizobium,and Rhizobium,had more contribution to Ma-HSF₂-1.（3）Six indexes in the measurement model of Melilotus albus in the field were significant,and there were six ways to affect Ndfa in the structural model.The results showed that there were 8 pathways for indigenous rhizobia to affect the nitrogen fixation ability of Melilotus albus.The effect of indigenous Rhizobia on the nitrogen accumulation of the whole plant was more significant after affecting the above ground and underground components 1（A1）and 1（R1）.The enhancement of nitrogen fixation ability of Melilotus albus has a positive effect on the above ground principal component3（A3）and the underground principal component 4 and 5（R4 and R5）,thus increasing the nitrogen accumulation of the whole plant.