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Genetic diversity of indigenous tropical fast-growing rhizobia isolated from soybean nodules

机译：大豆根瘤中土著热带速生根瘤菌的遗传多样性

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This study characterized genetically 30 fast-growing rhizobial strains isolated from nodules of Asian and modern soybean genotypes that had been inoculated with soils from disparate regions of Brazil. Analyses by rep-PCR (ERIC and REP) and RAPD indicated a high level of genetic diversity among the strains. The RFLP-PCR and sequencing analysis of the 16S rRNA genes indicated that none of the strains was related to Sinorhizobium (Ensifer) fredii, whereas most were related to Rhizobium tropici (although they were unable to nodulate Phaseolus vulgaris) and to Rhizobium genomic species Q. One strain was related to Rhizobium sp. OR 191, while two others were closely related to Agrobacterium (Rhizobium) spp.; furthermore, symbiotic effectiveness with soybean was maintained in those strains. Five strains were related to Bradyrhizobium japonicum and B. elkanii, with four of them being similar to strains carried in Brazilian inoculants, therefore modifications in physiological properties, as a shorter doubling time might have resulted from adaptation to local conditions. Phospholipid fatty acid analysis (PFLA) was less precise in delineating taxonomic relationships. The strains fit into eight Nod-factor profiles that were related to rhizobial species, but not to N2-fixation capacity or competitiveness. The data obtained highlight the diversity and promiscuity of rhizobia in the tropics, being capable of nodulating exotic legumes and might reflect ecological strategies to survive in N-poor soils; in addition, the diversity could also represent an important source of efficient and competitive rhizobial strains for the tropics. Putative new rhizobial species were detected only in undisturbed soils. Three species (R. tropici, B. japonicum and B. elkanii) were found under the more sustainable management system known as no-till, while the only species isolated from soils under conventional till was R. tropici. Those results emphasize that from the moment that agriculture was introduced into undisturbed soils rhizobial diversity has changed, being drastically reduced when a less sustainable soil management system was adopted.
机译：这项研究的特征是从亚洲和现代大豆基因型结核中分离出的30种快速生长的根瘤菌菌株，这些菌株已接种了巴西不同地区的土壤。 rep-PCR（ERIC和REP）和RAPD分析表明，这些菌株之间遗传多样性高。 RFLP-PCR和16S rRNA基因的测序分析表明，这些菌株均与费氏中华根瘤菌无相关性，而大多数菌株与热带根瘤菌有关（尽管它们无法结节菜豆）和根瘤菌基因组物种Q一种菌株与根瘤菌有关。 OR 191，另外两个与农杆菌属（Rhizobium）spp。密切相关；此外，在那些菌株中维持了与大豆的共生效力。五株与日本根瘤菌和B. elkanii有关，其中四株与巴西接种剂中携带的菌株相似，因此生理特性发生了变化，因为适应当地条件可能导致倍增时间缩短。磷脂脂肪酸分析（PFLA）在描述生物分类关系时不够精确。该菌株适合与根瘤菌属有关的8个Nod因子谱，而与N2 固定能力或竞争力无关。所获得的数据突出了热带根瘤菌的多样性和滥交性，能够结节外来豆科植物，并可能反映了在贫氮土壤中生存的生态策略；此外，多样性也可能代表热带地区高效而有竞争力的根瘤菌菌株的重要来源。仅在未受干扰的土壤中发现推定的新的根瘤菌物种。在更可持续的管理制度下，即免耕法发现了三种树种（R. tropici，B。japonicum和B. elkanii），而常规耕作下从土壤中分离出的唯一物种是R. tropici。这些结果强调，自从将农业引入未受干扰的土壤的那一刻起，根瘤菌多样性就发生了变化，当采用一种可持续性较差的土壤管理系统时，根瘤菌的多样性急剧下降。

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