Yet, this community exists within the nodule, albeit clearly outnumbered by nitrogen-fixing rhizobia. Even more striking is the incredibly diverse population of bacteria residing within nodules that elicit neither nodulation nor nitrogen fixation. Many of these nonrhizobial bacteria are nitrogen fixers, and some also induce nitrogen-fixing nodules on legume roots. However, other bacteria, which are not typical rhizobia, are often detected within nodules obtained from soil, thus revealing the existence of a phytomicrobiome where the interaction among the individuals is not only complex, but also likely to affect the behavior and fitness of the host plant. This article points out both current knowledge and gaps remaining to be filled for further interaction and improvement of a rhizobial commons.įor decades, rhizobia were thought to be the only nitrogen-fixing inhabitants of legume nodules, and biases in culture techniques prolonged this belief. It is worth noting that taxonomically important strains may not necessarily be important reference strains for other uses such as legume inoculation and genomics due to specialization of the different fields. Research and extension policies valorizing rhizobial germplasm diversity and preservation, farmer training for proper inoculant use and legal enforcement of commercial inoculant quality have proved a successful approach to promoting the use of forage legumes while enhancing biological N2 fixation. Forage legumes form another group of agronomically important legumes. Recent genetic characterization methods permit more reliable identification and will improve our knowledge of local populations. Bradyrhizobial inoculants for soybean are very diverse, yet classification and characterization of strains have long been difficult. Soybeans are major nitrogen-fixing crops in many parts of the world. Knowledge of the biodiversity of rhizobia and of local populations is important for the design of successful inoculation strategies. Nitrogen fixation in agriculture can be improved by inoculation of legume crops with suitable rhizobia. Symbiotic nitrogen fixation is the main route for sustainable input of nitrogen into ecosystems.
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