Exploiting inter-organismal chemical communication for improved inoculants

The combination of rising fossil fuel prices and a need to reduce greenhouse gas emissions will lead to expanded use of crop inoculants (bio-fertilizers) both for increased production of biomass (for bio-fuels and soil C storage) and to reduce production of nitrous oxide, through increased reliance on biological nitrogen fixation. Over the last century inoculants have been improved through strain selection, improved carriers (including sterile carriers), and increased cell densities. During the last few decades our understanding of signalling between symbiotic bacteria and plants has expanded enormously, with the signalling between rhizobia and their legume hosts being the model system. Recent work has shown that adverse environmental conditions can inhibit this signalling and that addition of plant-to-microbe signals into inoculants can help overcome this. This is also true of addition of the microbe-to-plant signals that act as the return signals of this system; however, they have also been shown to cause a general and direct stimulation of plant growth that is not yet well understood. Finally, very recent work has shown that some of the plant growth-promoting rhizobacteria produce novel signal compounds that stimulate plant growth. This is a time of rapid increase in understanding with regard to plant-microbe signalling; the use of these signals in commercial inoculants offers a new wave in innovations for this industry at a time when there is great need. Key words: Inoculants, rhizobacteria, rhizobia, signalling