Siderophoregenic Bradyrhizobia Boost Yield of Soybean

Abstract

After screening for siderophore (microbial iron chelator) production, of seven available cultures of soybean (Glycine max L.) root nodule bradyrhizobia, one strain, Bradyrhizobium japonicum NCIM 2746, was selected to confirm its phytopathogenic suppression and soybean growth promotion. Based on chromatographic and spectrophotometric studies, two different siderophores, a hydroxamate type (MW 734) and another catecholate type (MW 1000), were observed. Randomized block design (RBD) analysis of sick-pot studies (soil inoculated with phytopathogens) with an MACS 124 variety of soybean, bacterized with siderophoregenic B. japonicum, showed a marked increase in the percentage of germination, nodulation, chlorophyll, oil, protein content, and number of pods. Field trial study confirmed these pot results, which were evident from enhancement in shoot length, number of branches, chlorophyll content, number of nodules, root length, and number of pods. These results suggest the possibility of exploiting B. japonicum NCIM 2746 as a potential bioinoculant.

Relevance of Plant Growth Promoting Microorganisms and Their Derived Compounds, in the Face of Climate Change

“…Because of the interaction advantage, some microbes perform better in microbial consortia than when applied individually [70,89]. However, the reverse is true for some PGPM species, as reported by other researchers [70,92,100].…”

“…Although various strains that possess desirable properties under laboratory and greenhouse conditions may be isolated, developing a commercial product, effective under field conditions, is not an easy task, especially because numerous factors determine the efficiency of introduced species. Characteristics such as: possession of multiple mechanisms of enhancing plant growth, ability to compete favorably and establish populations in the rhizosphere, persistence in the rhizosphere over seasons, and ability to be cultured in artificial environments [15,61,89] are desired for potential PGPM strains. However, many plant and soil factors, such as plant species, soil temperature, composition and prevalence of native microbes, soil pH, etc., may work together against a strain which is otherwise excellent under controlled environment conditions.…”

“…Microbial consortia technology involves the use of more than one microbial species in a single inoculant product. The microbes may have the same or different modes of action [18,70,89], and may be from different phyla, genera or even other groupings, for example, a combination of bacterial and fungal strains. Microbial consortia may have an advantage over single strains when the species synergistically interact and confer benefits to each other [70,71,89,117].…”

“…The microbes may have the same or different modes of action [18,70,89], and may be from different phyla, genera or even other groupings, for example, a combination of bacterial and fungal strains. Microbial consortia may have an advantage over single strains when the species synergistically interact and confer benefits to each other [70,71,89,117]. For instance, one strain may breakdown a substrate, unavailable to other species, converting it into forms that the other members of the consortium can utilise as a source of nutrients [14], or produce exopolysaccharides which offer protection against stress to all members of the consortium [134], produce compounds which are signals that activate plant growth promotion capability of other members of the consortium, through the production of plant growth stimulating compounds, that they would otherwise not produce, for instance, in pure culture.…”

“…Researchers have reported inefficient strains that became efficient in a consortium. For example, Santhanam et al [89] observed that the inclusion of two bacterial strains with insignificant effects on mortality of sudden wilt pathogens in tobacco, in a consortium with three other bacteria improved resistance of plants to the same pathogen, in comparison to the consortium of 3 used alone. Mycorrhizal fungi, in association with a helper bacterium, may have better established mycelia and plant root colonisation, if the bacterium produces substances that directly enhance the germination of fungal spores, or indirectly enhance the establishment of mycorrhiza through the production of antimicrobials that reduce competition from other microbes or minor pathogens [14].…”