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Soybean (Glycine max), the primary source of high-quality plant protein, plays a crucial role as a grain and oil crop in China. Harnessing the full potential of symbiotic nitrogen fixation in soybean production holds immense significance for agriculture and ecology alike. Zhongdou 63, a newly developed early-maturing summer soybean cultivar in 2021, exhibits remarkable traits such as high yield, superior quality, multi-resistance, and wide adaptability. In this study, eight distinct rhizobia strains from diverse regions were meticulously screened to identify highly effective strains specifically suited for Zhongdou 63. The aboveground biomass, plant height, chlorophyll content, root length, nodule number, and nodule dry weight of Zhongdou 63 were measured and the data were subjected to statistical analysis. The results demonstrated that Y63-1 is a predominant strain of Zhongdou 63. Subsequently, we conducted further investigations on the broad-spectrum nodulation characteristics of Y63-1. Ten representative soybean cultivars were individually inoculated with Y63-1 and subsequently analyzed for nodule numbers and nodule dry weight in their symbiotic systems with rhizobia. The findings revealed that Y63-1 effectively formed nodules with all ten soybean varieties tested. In summary, our current study identified highly efficient broad-spectrum Bradyrhizobium elkaniistrain Y63-1 as the predominant strain in Zhongdou 63 and provided a theoretical foundation for enhancing yield potential not only in Zhongdou 63 but also in other varieties through inoculation with highly efficient rhizobia in production.

Soybean (Glycine max) is one of the most important economic legume crops with largest planting area, and is also an important oil crop, as well as food and feed material. Soybean-rhizobia symbiosis plays important roles in plant cultivation and fertilizer application. However, there are many problems in agricultural application of soybean symbiotic nitrogen fixation. In this review, we summarized three restriction factors (host specificity, low nitrogen fixation efficiency and abiotic stress) and discussed research progresses of these factors. Clarification of host specific mechanism will help to select and apply rhizobia inoculants. Both maintaining high nitrogenase activity and delaying nodule senescence can improve the efficiency of symbiotic nitrogen fixation. Abiotic stress-tolerant rhizobia can improve the abiotic stress tolerance of soybean. Breeding stress tolerant genotypes of soybean and rhizobia, obtaining correlated genes are the common strategies to improve soybean symbiotic nitrogen fixation under extreme conditions. Regulatory mechanisms of these restriction factors are still poorly understood and needs further clarification.