Screening Of Soybean And Rhizobial Strains And Mapping Of Genes For Controlling Nitrogen Fixation In Soybean Cultivars At Seedling Stage

Nitrogen demand of soybean can be supplied via biological nitrogen fixation. However, with the increasing of nitrogen fertilizer, it not only inhibits nitrogen fixation between soybean and rhizobium, but brings disadvantages to ecological environment. Therefore, it is important to study the characteristics of nitrogen– fixation for sustainable development of ecological environment. In this study, interactions between different soybean varieties and different Rhizobial strains were identified. It was found that Hefeng 25 and Guxin under inoculating B. japonicum strain 2178 had great difference in nodulatin and nitrogen fixation. Then the F11 populations of Hefeng 25 and Guxin inoculation B. japonicum strain 2178 were identifided at seedling stage too. QTL mapping was performed by characteristics of nitrogen fixation trait combined with software of Mapmaker. The main results are as follows:1. Difference of nodulation characteristic of different Rhizobial strainsFour B.japonicum including USDA110, USDA110-A, 113-2, 2178 and three S. fredii including WHG12, HH103, B16 have broad-spectrum nodulated ranges. S.fredii WHG12, B16, USDA205T and HH103 have the highest nodulation rate(above 80%). The Sinorhizobium fredii 2053 and J19-1 have the lowest nodulation rate(only 25%).2. Difference of nodulation characteristic of different soybean varietiesThe nodulation rate of Suinong 14, Zheng 92116, Shang 951099, Beijing xiao hei dou reached 100% with B.japonicum. Hefeng 25 have also higher nodulation rate which reached 85%; The nodulation rate of Suinong 20, Heinong 44 with B.japonicum were 33.3% and 42.9% respectively, which were lower nodulation cultivars. At the same time, the nodulation rate with S.fredii about Beijing xiao heidou, Zheng 92116, shang 951099 and Guxin reached 100%; The nodulation rate of other soybean reached between 40% and 67% with strains. Requirements on matching ability of S.fredii are stricter than B.japonicum.Of the three pairs of hydrin, Shang 951099 and Guxin didn't have significant differences with eighteen S.fredii. The other two symbiotic combinations such as Sui nong 14 and Sui nong 20, Hefeng 25 and Guxin have significant differences with B.japonicum 2178 and Hefeng25×Guxin have signidficant differences with S.fredii USDA205T(at 0.05 level).3.QTL mapping analyse about nodulation and nitrogen of RIL populationAll the nitrogen fixation traits at seeding stage showed a distribution in RIL population of He feng 25 and Gu xin, which were suitable to normal distribution and QTL mapping analysis.The regression analysis identified eleven significant associations between the marker loci and QTLs. Eight QTLs on chromosomes A1,L,D1b,D2,C2,I and O associated with nodulation traits at seedling stage detected which explained the range of the observed phenotypic variance from 7.26% to 15.05%, Among them, controlling nitrogen fixation activity QTL, located between satt005 and satt717 of linkage group A1, satt498～satt486 of linkage group D2, controlling nodule weight QTL, located between satt376 and satt256 of linkage group C2, satt162 and satt292 of linkage group I, controlling number of lateral root located between satt418 and satt523 of linkage group L, satt633 and 679 of linkage group O and satt073～satt050 of linkage group A1,which could respectively account for range of the observed phenotypic variance 9.3%,7.26%,11.8%. Controlling shoot dry weighe located between satt005 and satt600 of linkage group D1b.