Azospirillum sp. in current agriculture: From the laboratory to the field

Azospirillum sp., one of the best studied genus of plant growth promoting rhizobacteria, are able to colonize hundreds of plant species and improve their growth, development and productivity. Free nitrogen fixation and additive mechanisms related to the ability of Azospirillum sp. to produce phytohormones and other related molecules are proposed for explaining the plant growth promotion effects on inoculated plants, mainly under stressing conditions. Under field evaluations, the benefits of Azospirillum sp. inoculation, mostly related with plant attributes defined during early growth, can be related with the increase in the root development enlarging the explored soil volume for nutrients and water acquisition. Recently published reports of Azospirillum sp. inoculation of dryland crops showed grain yield responses on winter (14.0%) and summer cereals (9.5%) and also on legumes (6.6%). These responses are barely observed under strong stressful growing conditions (i.e. severe droughts, major nutrients limitations, etc.) and are currently obtained 70% of the time because the complex interaction between the modes of action of Azospirillum sp. and plants, the methods of inoculation and diverse crop production conditions. The practice of inoculating with selected strains of Azospirillum sp. provides a direct contribution increasing crop yields and enhance the efficacy in the use of production resources with extended benefits to the environment. One of the achievements from the research is the commercial use of azospirilla inoculants in approximately 3.5 million ha, mainly cultivated with cereals in South America. However, more coordinated communication programs of its complementary benefits for the development of sustainable crop production practices are still needed.