Department of Soil Science, University of Minnesota, St. Paul, Minnesota 55108.
Appl Environ Microbiol. 1984 Apr;47(4):607-12. doi: 10.1128/aem.47.4.607-612.1984.
Rhizosphere response was studied as a factor in competition among indigenous Rhizobium japonicum serogroups for the nodulation of soybeans under field conditions. R. japonicum serogroups 110, 123, and 138 were found to coexist in a Waukegan field soil where they were determined to be the major nodulating rhizobia in soybean nodules. Competitive relationships among the three serogroups in that soil and in rhizospheres were examined during two growing seasons with several host cultivars with and without inoculation and with a nonlegume. Enumeration of each of the three competitors was carried out on inner rhizosphere and nonrhizosphere soil by immunofluorescence with serogroup-specific fluorescent antibodies. Rhizobia present in early- and late-season nodules were identified by fluorescent antibody analysis. Populations of each serogroup increased gradually in host rhizospheres, not exceeding 10/g of rhizosphere soil during the first few weeks after planting, whereas numbers in fallow soil remained at initial levels (10 to 10/g). The rhizosphere effects were minor in host plants during this period of nodule initiation and were about the same for all three serogroups. Although serogroup 123 gave no evidence of dominance in early host rhizospheres, it clearly dominated in nodule composition, occupying 60 to 100% of the nodules. High densities of all three serogroups were observed in host rhizospheres during flowering. Rhizosphere populations, especially of serogroup 123, were still high during pod fill and seed maturation. The rhizosphere responses of the R. japonicum serogroups were much greater with the soybean cultivars than with oats, but even in host rhizospheres the R. japonicum populations were greatly outnumbered by other bacteria. The success of serogroup 123 in achieving nodulation does not appear to be due to superior colonization of the host rhizosphere.
根际反应是研究土著大豆根瘤菌血清群在田间条件下竞争结瘤的一个因素。在沃基根田间土壤中发现，根瘤菌血清群 110、123 和 138 共存，它们被确定为大豆根瘤中的主要结瘤根瘤菌。在两个生长季节，用几种有接种和无接种的宿主品种以及一种非豆科植物，在该土壤和根际中研究了这三个血清群之间的竞争关系。用血清群特异性荧光抗体通过免疫荧光对每个竞争群体的内根际和非根际土壤进行了计数。用荧光抗体分析鉴定了早季和晚季根瘤中的根瘤菌。每个血清群的种群在宿主根际中逐渐增加，在种植后最初几周内，根际土壤中不超过 10/g，而休耕土壤中的数量保持在初始水平（10 到 10/g）。在这个结瘤起始期间，根际效应在宿主植物中较小，对所有三个血清群的影响基本相同。尽管血清群 123 在早期宿主根际中没有表现出优势，但它在结瘤组成中明显占主导地位，占据了 60%到 100%的根瘤。在开花期，所有三个血清群在宿主根际中都观察到高密度。在豆荚填充和种子成熟期间，根际种群，特别是血清群 123 的种群仍然很高。与燕麦相比，大豆品种的根瘤菌血清群的根际反应更大，但即使在宿主根际中，根瘤菌种群也远远超过其他细菌。血清群 123 成功结瘤似乎不是由于其对宿主根际的优越定殖。
