Endophytic bacteria and their role in legumes growth promotion

Abstract

The rhizosphere and the phylloplane of plants are habitats for large number of microorganisms. The study of plant-associated bacteria is important not only for understanding their role in these interactions but also for biotechnological application in areas as the plant growth promotion. Legume plants are able to form nitrogen-fixing nodules by symbiotic association with soil bacteria collectively known as rhizobia. Even when the term root nodule bacteria has been exclusively applied to rhizobia, nonsymbiotic endophytic bacteria from several genera have been isolated from legume nodules, and this is the main topic of this chapter. Endophytes are defined as those microorganisms isolated and detected inside the tissues by microscopic methods, which maintain their ability to infect plants, being rhizobia the most studied group. Endophytic bacteria can positively influence plant growth through different mechanisms, such as fixation of atmospheric nitrogen, solubilization of phosphates, and protection against pathogens, among others. Therefore, a wide number of studies have been and still are focused in plant-growth-promoting bacteria as potential supplements of fertilizers, herbicides, fungicides, etc. For endophytes to exert beneficial effects on plant growth, they should be in an intimate relationship with the host plant. The signaling cascade involved in legume-rhizobia interaction that leads to nodule development as well as recent knowledge about the taxonomy of this bacterial group are also described.