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is available at the end of the articleIntroduction Sustainability probably represents the greatest challenge to increase food production. Year after year, the agricultural sector is forced to adopt new technologies to maintain high yields—without clearing new land for agriculture—and to minimize degradation of land that is occurring worldwide. Since the Green Revolution, the use of chemical fertilizers has played a key role in increasing yields; however, costs are often a major limitation to farmers in developing and poor countries, whereas, for developed countries, pollution of water and soil by fertilizers and greenhouse-gas emis-sions are sources of concern. Bio-fertilizers can help meet the demands of sustain-able, productive agriculture at low cost. Rhizobial inocu-lants have been applied to legume crops for over 120 years as bio-fertilizers, and inoculants carrying plant-growth-promoting rhizobacteria (PGPR) have been used in agriculture for over half a century (Okon an