Revisiting the plant growth-promoting rhizobacteria: lessons from the past and objectives for the future.

Plant beneficial rhizobacteria (PBR) is a group of naturally occurring rhizospheric microbes that enhance nutrient availability and induce biotic and abiotic stress tolerance through a wide array of mechanisms to enhance agricultural sustainability. Application of PBR has the potential to reduce worldwide requirement of agricultural chemicals and improve agro-ecological sustainability. The PBR exert their beneficial effects in three major ways; (1) fix atmospheric nitrogen and synthesize specific compounds to promote plant growth, (2) solubilize essential mineral nutrients in soils for plant uptake, and (3) produce antimicrobial substances and induce systemic resistance in host plants to protect them from biotic and abiotic stresses. Application of PBR as suitable inoculants appears to be a viable alternative technology to synthetic fertilizers and pesticides. Furthermore, PBR enhance nutrient and water use efficiency, influence dynamics of mineral recycling, and tolerance of plants to other environmental stresses by improving health of soils. This report provides comprehensive reviews and discusses beneficial effects of PBR on plant and soil health. Considering their multitude of functions to improve plant and soil health, we propose to call the plant growth-promoting bacteria (PGPR) as PBR.

Evaluation of potassium solubilizing rhizobacteria (KSR): enhancing K-bioavailability and optimizing K-fertilization of maize plants under Indo-Gangetic Plains of India.

Imbalanced potassium (K) fertilization in agricultural fields has led to considerable negative impacts and remains to be the foremost challenge for maize production in India-Gangetic region. Plant growth-promoting rhizobacteria, particularly potassium solubilizing rhizobacteria (KSR), could serve as inoculants and a promising strategy for enhancement of plant absorption of K hence reducing dependency on chemical fertilizers. Maize seeds were microbiolized for 30 min with KSR suspensions. In the present study, the use of chemical fertilizers along with Agrobacterium tumefaciens strain OPVS10 showed pronounced beneficial effect on growth and yield attributes in maize. There was a significant difference among different parameters studied when varying doses of K and KSR strains were applied. Results showed that the combined application of KSR strain OPVS10 with 100% RDK (recommended dose of K) was most effective in modulating growth, physio-biochemical, and yield attributes in maize thus could be regarded as a promising alternative to mineral K-fertilization. Principal component analysis (PCA) revealed that 100-grain weight and grain yield were the most important properties to improve the sustainable growth of maize. Therefore, these KSR strains have different mechanisms for modulating various activities in maize plants. Results suggested that the synergistic application of KSR strain OPVS10 with 100% RDK can be used for optimized breeding, screening, and nutrient assimilation in maize crop. Hence, this eco-friendly approach may be one of the efficient methods for reducing dependency on chemicals, which pose adverse effects on human health directly and indirectly.