Potential use of rhizobium for vegetable crops growth promotion

Abstract

The system of vegetable crops production required large amounts of mineral fertilizers. One of the possible alternatives to assure the economic and environmental sustainability of this production system would be the use of promoting growth plant rhizobacteria (PGPR). However, care is needed to select a microorganism to be used in crops that are usually consumed raw, so human health is not at risk. It was important to search for PGPR, as rhizobium, that already were broadly used as inoculants for leguminous plants for several decades, without risks to human health. PGPR can promote growth and development of plants through direct and indirect mechanisms, by production and secretion of chemical substances in the rhizosphere. The direct mechanisms were involved with the uptake of nutrients by the plants (nitrogen, phosphorus and essential minerals) through phosphate solubilization, production of siderophores and growth regulators. The indirect mechanisms were involved with the decrease of inhibitory effects from various pathogenic agents related with biological pest control, thereby favoring plant growth. Nevertheless, due to its ability to promote beneficial effects to plants, effective bacterial colonization was extremely important. Some bacteria that colonized the rhizoplane may penetrate the plant roots and some strains may move to the aerial part, with decreased bacterial density, compared with colonizing populations in the rhizosphere or roots. It can be concluded that Rhizobia promotes plant growth using different mechanisms as biological nitrogen fixation and production of different plant growth regulators (e.g. auxins). Therefore, new studies with Rhizobia characterization and observation about its different mechanisms of promoting plant growth should be performed. Such information would be useful for the identification of plants with potential to increase agricultural production due to the benefits of using plant growth promoter’s rhizobia.