Plant Growth-Promoting Diazotrophs: Optimising their Role as Key Agents in Achieving More Efficient Nutrient Use by Field Crops

There are widespread attempts by scientists and commercial producers to improve yields of crop plants with plant growth-promoting rhizobacteria (PGPR). Importantly, there is now statistically significant evidence (e.g., Nguyen et al., 2003) that benefits from inoculation can be obtained under field conditions, so reducing the need for high inputs of nutrients particularly nitrogen and providing significant economic benefits to farmers. We have advanced the hypothesis that diazotrophs are specially adapted to this PGPR role (Kennedy et al., 2004), because their ability to grow in conditions of high C:N ratios. However, such diazotrophic PGPRs do not yet provide a technology recognised as reliable enough to justify their application to crops such as rice and wheat on a global scale.