Abstract
Intensification of agricultural land and the overuse of inorganic fertilisers has led to soil acidification, depletion of organic matter, and environmental pollution. Approaches to protect soil health, including the enhancement of microbial diversity, are integral to improving crop productivity and food security. Metagenomics has rapidly improved our understanding of soil microbial diversity and function, while genetic techniques have helped to dissect the complex signal exchange between microorganisms and plants. This article presents and evaluates reported beneficial effects of plant growth-promoting bacteria (PGPB), focussing on those capable of mobilising or solubilising nutrients and/or stimulating plant growth when applied to agriculturally important grasses. The agricultural industry has capitalised on these scientific advancements, generating microbial formulations for specific crop responses. However, scientific methodologies must be applied in order to overcome inherent limitations of many PGPBs including their inability to be cultured, their poorly defined or multiple modes of action, a low level of integration with the crop partner, and an unpredictability in translating beneficial plant responses to the field. Novel approaches such as engineered rhizospheres, enhancing endophytic systems, cereal nodule development, and the use of inoculant consortiums will be necessary to sustain growth in the biofertiliser industry.