Abstract

In the last decades, many efforts have been made to achieve a more sustainable agriculture, resulting from the economic and environmental needs of increasing food production with lower inputs of fertilizers and pesticides. In this context, there is a growing interest in exploring the beneficial activity of microbes, especially rhizosphere bacteria, collectively known as plant growth-promoting rhizobacteria (PGPR). Several studies have shown that many bacterial strains, belonging to different genera, isolated from soil and rhizosphere of plants, can effectively promote plant growth by means of direct and indirect mechanisms [1]. Despite the indisputable importance of PGPR for sustainable agriculture, the availability of inoculants for farmer scale is still scarce. The rising number of studies demonstrating the efficacy of new PGPR strains in many crop species does not result in a proportional rise of new inoculant products. In Brazil, a country with a long history of research and use of inoculants, there are only 12 PGPR strains authorized for the production of inoculants, which are recommended for only four species: rice, wheat, maize and eucalyptus [2]. This situation remains unchanged since 2011, although the efforts of numerous research groups. In the rest of the world, the situation is not much different. Some of main constraints to make available new inoculant products are linked to complex regulatory policies in each country [3]. Moreover, PGPR inoculants often show problems of stability during formulation and storage stages [3] and even registered PGPR inoculant products may have variable efficiency depending on soil, climate and plant genotype [4].