| Nitrogen nutrients necessary for plant growth can be obtained through absorption of synthetic chemical nitrogen fertilizer and biological nitrogen fixation.Artificial nitrogen application has high cost and low utilization rate,and excessive application seriously pollutes the environment and soil.Biological nitrogen fixation is a process in which nitrogen-fixing bacteria reduce nitrogen in the air to ammonium nitrogen that can be used by plants through their own nitrogenase system.It does not consume energy and does not pollulate the environment.It is a kind of green and sustainable development way of agriculture with high efficiency of resource utilization and environment friendly.The symbiotic nitrogen fixation system of soybean and other leguminous crops with rhizobia is the most efficient in biological nitrogen fixation,making it a key source of nitrogen in agro-ecosystem.Use rhizobia to fix nitrogen this one natural means realizes reduce weight target,already caused more and more people to take seriously.Biological nitrogen fixation system plays an important role in soybean production in the United States,Brazil and other countries.Agricultural practice has basically abandoned this tradition inherited for thousands of years in China.In order to make better use of this symbiotic nitrogen fixation system,this study isolated,identified and classified indigenous rhizobia from Shanxi Province.Rhizobium bacteria with good symbiotic nitrogen fixation effect were selected by matching with main soybean varieties of Shanxi Province.Phenotypic variation and genetic analysis were carried out in RIL populations of Jinda 53 and Pingnan crosses.QTLs for traits related to nodule nitrogen fixation were mapped by compound interval mapping.Specific research results are as follows:(1)In this study,187 strains of rhizobia isolated from Guangling Datong,Taigu Jinzhong and Qingxu Taiyuan of Shanxi Province could all amplifies nif H and nod A genes.Among them,172 strains were fast rhizobia belonged to S.fredii and BTB staining turns yellow,the dominant bacteria in Shanxi Province,while15 strains were slow rhizobia belonged to B.diazoefficiens and B.daqingense,respectively,and BTB staining turns blue.BOX-PCR clustering showed that the isolated rhizobia were divided into 16 classes,indicating that Shanxi Province was rich in rhizobia resources and diverse in species.(2)Rhizobium with good salt tolerance TG1,TG14,TG16,TG44,TG53,TG79 and GL93 were screened out,which were all resistant to 1% Na Cl,and TG14,TG16,TG44 and TG53 could grow on 2% Na Cl plate.Under salt stress,the root nodule character decreased more than the plant character,indicating that the root nodule is more sensitive to salt stress.Inoculating rhizobia can alleviate the damage caused by salt stress and improve salt resistance of soybean.Under 100 m M Na Cl stress,TG1 and TG14 were the salt-tolerant rhizobia with better matching with Jinda 88.The results showed that GL11 and GL43 had better matching ability with Jinda 88,and the biomass of shoot,root and nodules increased by 22.2% ～ 41.5% compared with USDA110 inoculation.TG37 matched well with Kefeng 1,and its shoot dry weight,root dry weight,nodule fresh weight,nodule dry weight and nodule number increased by 15.0% ～ 60.6% compared with USDA110 inoculation.The rhizobia resources were provided for the subsequent field experiments.(3)Different soybean rhizobium bacteria were inoculated into the parents.Rhizobium TG44,which showed significant difference in the nodule traits of the parents,was screened out and inoculated with RIL population.The nodule related indexes were measured at the seedling and flowering stages.Each trait had a bidirectional superparent distribution.The variation of nodule characters was greater than that of plant characters.There were some extreme individuals in root nodule characters.The characteristics related to nodule in RIL population were determined at the flowering stage.The results showed that the total nodule dry weight was positively correlated with nodes number,branches number,shoot dry weight and root dry weight.Average fresh weight of total nodule and average dry weight of total nodule were significantly positively correlated with root dry weight.Number of total nodules was positively correlated with the nodes number,and negatively correlated with the fresh root weight.A total of 51 QTL loci were mapped for the nodule and nitrogen fixation related traits at seedling and flowering stage of soybean,and 5.8% ～ 13.2% of the genetic variation of nodule and nitrogen fixation related traits in RIL population was explained,respectively.There were 7 QTL loci that were repeatedly identified with previous QTL loci and 44 QTL loci were newly mapped.Two candidate genes,Glyma.06G126700 and Glyma.14G214700,were found to be highly expressed in nodules by bioinformatics analysis based on QTL loci that were repeatedly with previous QTL loci and jointly mapped in nodules,which could be used as the key genes for further research. |
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