Segregation of nod‐containing and nod‐deficient bradyrhizobia as endosymbionts of Arachis hypogaea and as endophytes of Oryza sativa in intercropped fields of Bengal Basin, India

Abstract

Bradyrhizobial invasion in dalbergoid legumes like Arachis hypogaea and endophytic bacterial invasions in non-legumes like Oryza sativa occur through epidermal cracks. Here, we show that there is no overlap between the bradyrhizobial consortia that endosymbiotically and endophytically colonise these plants. To minimise contrast due to phylogeographic isolation, strains were collected from Arachis/Oryza intercropped fields and a total of 17 bradyrhizobia from Arachis (WBAH) and 13 from Oryza (WBOS) were investigated. 16SrRNA and concatenated dnaK-glnII-recA phylogeny clustered the nodABC-positive WBAH and nodABC-deficient WBOS strains in two distinct clades. The in-field segregation is reproducible under controlled conditions which limits the factors that influence their competitive exclusion. While WBAH renodulated Arachis successfully, WBOS nodulated in an inefficient manner. Thus, Arachis, like other Aeschynomene legumes support nod-independent symbiosis that was ineffectual in natural fields. In Oryza, WBOS recolonised endophytically and promoted its growth. WBAH however caused severe chlorosis that was completely overcome when coinfected with WBOS. This explains the exclusive recovery of WBOS in Oryza in natural fields and suggests Nod-factors to have a role in counterselection of WBAH. Finally, canonical soxY1 and thiosulphate oxidation could only be detected in WBOS indicating loss of metabolic traits in WBAH with adaptation of symbiotic lifestyle.

Long-term monoculture reduces the symbiotic rhizobial biodiversity of peanut

“…I 60,954 (Table S3) is unclear since they formed effective nodules on peanut. Some of these strains harboring nifH but not nodC may indicate that they nodulate with peanut using a nod-independent mode, as previously reported [10]. Therefore, in contrast to B. huanghuaihaiense, the other 7 genospecies are effective microsymbionts for peanut.…”

Phylogeny and Phylogeography of Rhizobial Symbionts Nodulating Legumes of the Tribe Genisteae

“…and their adaptability to various edaphic and climatic conditions, resulting in this genus having a broad geographical range [ 21 , 97 ]. Bradyrhizobia are common in soils in places where legumes are absent, which may explain the loss of nodulating ability by portions of rhizobial communities [ 98 , 99 , 100 ]. Indeed, Bradyrhizobium communities comprise both nodulating and non-nodulating bacteria, and the latter may even lack the capacity to fix nitrogen [ 101 ].…”

“…Indeed, Bradyrhizobium communities comprise both nodulating and non-nodulating bacteria, and the latter may even lack the capacity to fix nitrogen [ 101 ]. In phylogenetic trees, these non-nodulating, non-diazotrophic bradyrhizobia are often indistinguishable from symbiotic strains [ 100 ]. The lack of symbiotic properties may, however, be compensated by other attributes as revealed in bradyrhizobia inhabiting forest soil habitats that are rich in organic matter, whose genomes are enriched in loci involved in the catabolism of aromatic compounds [ 102 ].…”

Nitrogen Challenges and Opportunities for Agricultural and Environmental Science in India

“…Both WBOS or WBAH type strains are able to nodulate peanut, however only WBAH strains do it in an effective way. Furthermore, both groups of strains promote growth on peanut and rice plants under control conditions (Guha et al, 2016).…”