Selection of host-plant genotype: The next step to increase grain legume N2fixation activity

Abstract

Symbiotic N2fixation research thus far has been primarily focused on selection of bacteria. However, little progress in impacting crop yields has resulted from this approach. Bacteria introduced in field soils rarely compete well with indigenous bacteria, including mutated lines selected for high nitrogen fixation capacity. Consequently, introduction of 'elite' bacteria in fields commonly does not result in crop yield increase. This review highlights that the primary regulation of N2fixation is a result of response of integrated physiological activity at the plant level. Nitrogen feedback from the host plant plays an important role in regulating the N2fixation rate. Rapid sequestration of fixed nitrogen by the plant is especially important for high N2fixation activity. In addition, water cycling in the plant between the shoot and nodules plays a key role in sustaining high N2fixation activity. Therefore, attention in selecting the host-plant genotype is suggested to be the next step to increasing N2fixation activity of grain legumes.