Non-rhizobia are the alternative sustainable solution for growth and development of the nonlegume plants

The major research focus for biological nitrogen fixation (BNF) has mostly been on typical rhizobia with legumes. But the newly identified non-rhizobial bacteria, both individually or in combination could also be an alternative for nitrogen supplementation in both legumes and nonlegume plants. Although about 90% of BNF is derived from a legume - rhizobia symbiosis, the non-legumes specially the cereals lack canonical nitrogen fixation system through root-nodule organogenesis. The non-rhizobia may colonize in the rhizosphere or present in endophytic/associative nature. The non-rhizobia are well known for facilitating plant growth through their potential to alleviate various stresses (salt, drought, and pathogens), acquisition of minerals (P, K, etc.), or by producing phytohormones. Bacterial symbiosis in non-legumes represents by the Gram-positive Frankia having a major contribution in overall fortification of usable nitrogenous material in soil where they are associated with their hosts. This review discusses the recent updates on the diversity and association of the non-rhizobial species and their impact on the growth and productivity of their host plants with particular emphasis on major economically important cereal plants. The future application possibilities of non-rhizobia for soil fertility and plant growth enhancement for sustainable agriculture have been discussed.

Automated summary

Previous research on biological nitrogen fixation has mainly focused on the symbiotic relationship between legumes and rhizobia. However, newly identified non-rhizobial bacteria can also be used as an alternative nitrogen source for both legumes and non-legume plants. Non-legume plants, particularly cereals, lack the canonical nitrogen fixation system through root-nodule organogenesis. Non-rhizobial bacteria can colonize in the rhizosphere or exist in an endophytic/associative manner. They are known for promoting plant growth, alleviating various stresses, acquiring minerals, and producing phytohormones. In non-legume plants, bacterial symbiosis, particularly with Gram-positive Frankia, plays a major role in the overall availability of usable nitrogen in the soil. This review discusses the diversity and association of non-rhizobial species and their impact on the growth and productivity of major economically important cereal plants. The potential application of non-rhizobia for improving soil fertility and enhancing plant growth for sustainable agriculture is also discussed.