The application of plant growth promoting rhizobacteria (PGPR) in low input and organic cultivation of graminaceous crops; potential and problems

Although the uses of plant growth stimulating bacteria (PGPR) to improve the yield of graminaceous crops have been studied for over seventy years the utility of the technology remains uncertain. Increases in crop yield have often been inconsistent, reflecting a lack of understanding of the mechanisms by which PGPR exert their effects. Because PGPR are able to fix N2, this was initially assumed to boost crops by supplementing soil N. However, it is now clear, that for most free living PGPR, other mechanisms affecting root development, and nutrient uptake can account for the observed increase in crop yields. Here we review the current state of our understanding of PGPR in graminaceous crop cultivation, identifying their potential contribution to more sustainable agricultural practices but also highlighting issues that need to be addressed before this technology can be appropriately assessed as a replacement for inorganic N addition.