Competency of Rhizobial Inoculation in Sustainable Agricultural Production and Biocontrol of Plant Diseases

Abstract

The rate of growth of the global population poses a risk to food security, demanding an increase in food production. Much of the world's cultivable soils also do not have ideal farming conditions such as soil health and fertility problem and increased pest attacks, which are challenges of food production. In this perspective, there is a need to increase agricultural production using a more economically and environmentally sustainable approach. As practices of agricultural production and improvement, rhizobial inoculants represent a practically effective, ecologically safe, and economically alternative means of realizing maximum agricultural production. This review addressed how rhizobial inoculation advances agricultural production through improving plant growth, nutrient availability and uptake, and yields by enhancing bio-fixation of atmospheric nitrogen and solubilization of soil nutrients. Besides, rhizobial inoculants offer biocontrol of plant diseases by providing resistance against disease-causing pathogens or suppression of diseases. Mechanisms involved in biocontrol of plant diseases include competition for infection sites and nutrients, activation of induced systemic resistance, and production of substances such as growth hormones, antibiotics, enzymes, siderophores, hydrogen cyanide, and exo-polysaccharides. Consequently, this approach is promising as sustainable agricultural practices have yet to supplement or replace chemical fertilizers, serving as a basis for future research on sustainable agricultural production. Despite the multifunctional benefits of rhizobial inoculation, there is a variation in the implementation of this practice by farmers. Therefore, researchers should work on eradicating farmers' constraints in using rhizobia, and future studies should be concentrated toward the methods of improving inoculant quality and promotion of the technology.

Contribution, Utilization, and Improvement of Legumes-Driven Biological Nitrogen Fixation in Agricultural Systems

“…Modulation of stress response genes, phytohormone biosynthesis, phosphate solubilization, and antibiotic production in host plants are also important techniques for improving the symbiotic interaction and the effectiveness of BNF. Kebede (2021) also delineated that rhizosphere engineering can be an alternative approach through which plants are genetically modified to discharge compounds that boost the association and proliferation of beneficial microorganisms.…”

“…The most antique microbe used as inoculants is "rhizobia" bacteria that can colonize the rhizosphere and establish a symbiotic association with legumes, which are used as a plant growth promoter and protector through BNF, mobilization and solubilization of nutrients, production of siderophores, and discharge of phytohormones (Kebede, 2021). According to Murphy-Bokern et al (2017), inoculation of the legume with the appropriate strain of rhizobia is necessary production technology if it is to be grown where it or a related species has not been produced within the previous 5 years, and this inoculation often results in improved BNF and, hence, soil fertility and crop yields.…”

“…Hence, legume inoculation with rhizobia is a way of ensuring that the strain of rhizobia appropriate for the legume cultivar being grown exists in the soil at the proper period and in numbers adequate to make a rapid and effective infection and succeeding nitrogen fixation. The inventive objective of this practice is to stimulate BNF to offer nitrogenous nutrients to a particular legume and other crops, and its return is an increment in plant growth, nutrient uptake, yield, seed protein, and other traits and a reduction in the use of chemical fertilizers with the subsequent decrease of ecological contamination (Wolde-meskel et al, 2018;Kebede, 2021).…”

“…For effective nodulation and subsequent improvement in BNF, it is also imperative to improve the rhizosphere competence and survival of rhizobial inoculants and enhance their adaptation to diverse environments, which can be advantageous in producing a robust approach for usage by farmers (Kebede, 2021). It is reported that legume inoculation with effective rhizobia offers stimulation and accumulation of phenolic compounds, such as isoflavonoid phytoalexins, and triggering of enzymes such as L-phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), peroxidase (POX), and polyphenol oxidase (PPO), which are involved in phenylpropanoid and isoflavonoid pathways, a rich source of metabolites in plants (Das et al, 2017;Kebede, 2021).…”

“…For effective nodulation and subsequent improvement in BNF, it is also imperative to improve the rhizosphere competence and survival of rhizobial inoculants and enhance their adaptation to diverse environments, which can be advantageous in producing a robust approach for usage by farmers (Kebede, 2021). It is reported that legume inoculation with effective rhizobia offers stimulation and accumulation of phenolic compounds, such as isoflavonoid phytoalexins, and triggering of enzymes such as L-phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), peroxidase (POX), and polyphenol oxidase (PPO), which are involved in phenylpropanoid and isoflavonoid pathways, a rich source of metabolites in plants (Das et al, 2017;Kebede, 2021). Furthermore, Das et al (2017) recommended novel rhizobial formulation technologies, including polymerbased formulations, water-in-oil emulsion technology for producing liquid formulations, biofilm-based formulations, and application of nanotechnology for the manufacture of an effective inoculant that can ensure enhanced stability, survival, and competence as biofertilizers and biocontrol agents under adverse ecological conditions.…”