Characterization of Rhizobia for the Improvement of Soybean Cultivation at Cold Conditions in Central Europe

Abstract

In central Europe, soybean cultivation is gaining increasing importance to reduce protein imports from overseas and make cropping systems more sustainable. In the field, despite the inoculation of soybean with commercial rhizobia, its nodulation is low. In many parts of Europe, limited information is currently available on the genetic diversity of rhizobia and, thus, biological resources for selecting high nitrogen-fixing rhizobia are inadequate. These resources are urgently needed to improve soybean production in central Europe. The objective of the present study was to identify strains that have the potential to increase nitrogen fixation by and the yield of soybean in German soils. We isolated and characterized 77 soybean rhizobia from 18 different sampling sites. Based on a multilocus sequence analysis (MLSA), 71% of isolates were identified as Bradyrhizobium and 29% as Rhizobium. A comparative analysis of the nodD and nifH genes showed no significant differences, which indicated that the soybean rhizobia symbiotic genes in the present study belong to only one type. One isolate, GMF14 which was tolerant of a low temperature (4°C), exhibited higher nitrogen fixation in root nodules and a greater plant biomass than USDA 110 under cold conditions. These results strongly suggest that some indigenous rhizobia enhance biological nitrogen fixation and soybean yield due to their adaption to local conditions.

Soybean Nodulation Response to Cropping Interval and Inoculation in European Cropping Systems

“…The demand for soybeans from Europe is increasing, and there is a growing interest by farmers to experiment with the crop (Reckling et al, 2020) and to diversify their cropping systems that are dominated by cereals (Hufnagel et al, 2020). There are studies to identify potent indigenous and commercial Bradyrhizobia inoculants suitable for European conditions (Zimmer et al, 2016;Yuan et al, 2020) and attempt to incorporate soybeans in the no-till cover-crop system (Halwani et al, 2019). However, very little is known about the potential of soybeans in higher latitudes (Lamichhane et al, 2020;Schoving et al, 2020).…”

“…On the other hand, previously introduced strains, subsequently, might remain genetically isolated in soil or may undergo genetic changes to fit the local conditions (Perrineau et al, 2014). Indeed, inoculants are often applied to soils with soybean cultivation history and established SNB (Obaton et al, 2002;Narożna et al, 2015;Yuan et al, 2020). Little is known about the possible influences of the previously introduced SNB on the symbiotic performance of commercial inoculants.…”

Genotype and cytokinin effects on soybean yield and biological nitrogen fixation across soil temperatures

“…BNF depends on successful nodulation and rhizobial efficiency to fix atmospheric N 2 to ammonia. Previous work to mitigate the effects of low RZT on BNF have focused on identifying cold‐tolerant rhizobia (Kühling, Hüsing, Bome, & Trautz, 2018; Yuan et al, 2020; Zhang, Charles, Driscoll, Prithiviraj, & Smith, 2002; Zimmer et al, 2016). However, the success of rhizobial inoculants can depend on their persistence in the soil and competition with native rhizobia, with local strains better adapted to adverse conditions (Thilakarathna & Raizada, 2017).…”

A microbiome engineering framework to evaluate rhizobial symbionts of legumes

“…HGT is a natural process (Bamba et al 2019), but can be problematic in legume crop fields. Brazil has experienced issues with native rhizobia acquiring inoculant symbiotic genes contributing to the RCP for Soybeans (Barcellos et al 2007) and the same phenomenon has been reported for Soybeans grown in Europe (Yuan et al 2020). Conversely, reports of HGT in Australia have not impacted chickpea production (Elias and Herridge 2015).…”

“…Application of microbiome engineering at an agricultural scale would be extremely difficult, but simplified microbiome engineering can be used on a site-by-site basis to identify context dependent contributors to the RCP (Vessey 2004). For example, a rhizobia strain was isolated from a field in Germany that provides greater benefit to Soybean than an elite inoculant at near freezing temperatures (Yuan et al 2020). This suggests that beneficial rhizobia were already present in this soil, and microbiome engineering could be used to determine if, and how, the soil community could be shaped by Soybeans to enhance growth and seed pod production in cold conditions.…”