Table_8_Sinorhizobium fredii Strains HH103 and NGR234 Form Nitrogen Fixing Nodules With Diverse Wild Soybeans (Glycine soja) From Central China but Are Ineffective on Northern China Accessions.DOCX

Sinorhizobium fredii indigenous populations are prevalent in provinces of Central China whereas Bradyrhizobium species (Bradyrhizobium japonicum, B. diazoefficiens, B. elkanii, and others) are more abundant in northern and southern provinces. The symbiotic properties of different soybean rhizobia have been investigated with 40 different wild soybean (Glycine soja) accessions from China, Japan, Russia, and South Korea. Bradyrhizobial strains nodulated all the wild soybeans tested, albeit efficiency of nitrogen fixation varied considerably among accessions. The symbiotic capacity of S. fredii HH103 with wild soybeans from Central China was clearly better than with the accessions found elsewhere. S. fredii NGR234, the rhizobial strain showing the broadest host range ever described, also formed nitrogen-fixing nodules with different G. soja accessions from Central China. To our knowledge, this is the first report describing an effective symbiosis between S. fredii NGR234 and G. soja. Mobilization of the S. fredii HH103 symbiotic plasmid to a NGR234 pSym-cured derivative (strain NGR234C) yielded transconjugants that formed ineffective nodules with G. max cv. Williams 82 and G. soja accession CH4. By contrast, transfer of the symbiotic plasmid pNGR234a to a pSym-cured derivative of S. fredii USDA193 generated transconjugants that effectively nodulated G. soja accession CH4 but failed to nodulate with G. max cv. Williams 82. These results indicate that intra-specific transference of the S. fredii symbiotic plasmids generates new strains with unpredictable symbiotic properties, probably due to the occurrence of new combinations of symbiotic signals.

费氏中华根瘤菌（Sinorhizobium fredii）土著种群在华中各省分布广泛，而慢生根瘤菌属（Bradyrhizobium）物种（包括大豆慢生根瘤菌Bradyrhizobium japonicum、固氮慢生根瘤菌B. diazoefficiens、埃尔坎慢生根瘤菌B. elkanii等）在北方与南方各省更为丰富。研究人员以采自中国、日本、俄罗斯及韩国的40份野生大豆（Glycine soja）种质资源为材料，探究了不同大豆根瘤菌的共生特性。慢生根瘤菌菌株可使所有供试野生大豆结瘤，尽管不同种质间的固氮效率存在显著差异。费氏中华根瘤菌HH103与华中地区野生大豆的共生能力，明显优于其与其他地区野生大豆种质的共生效果。曾被报道寄主范围最广的根瘤菌菌株——费氏中华根瘤菌NGR234，同样可与华中地区的多份野生大豆种质形成具有固氮能力的根瘤。据我们所知，这是首次报道费氏中华根瘤菌NGR234与野生大豆间形成有效共生关系的研究。将费氏中华根瘤菌HH103的共生质粒转移至经共生质粒消除（pSym-cured）的NGR234衍生菌株（菌株NGR234C）后，所得接合转移子可与栽培大豆（Glycine max）品种Williams 82以及野生大豆种质CH4形成无效结瘤。与之相反，将共生质粒pNGR234a转移至费氏中华根瘤菌USDA193的经共生质粒消除的衍生菌株后，所得接合转移子可有效结瘤野生大豆种质CH4，但无法结瘤栽培大豆品种Williams 82。上述结果表明，费氏中华根瘤菌共生质粒的种内转移可产生共生特性难以预测的新型菌株，这可能源于共生信号的全新组合。