Rhizobia in rotation system of irrigated rice and hibernal leguminous forages

Abstract

In areas of cultivated flooded soil, adapted rhizobia to water stress can form nodules in hibernal legumes, fix nitrogen, and even colonize the non-leguminous plant species, such as gramineous plants. Recent studies have shown that rhizobia can colonize roots, stems and leaves of grasses, promoting plant growth. The production of plant hormones, mainly indole acetic acid (IAA), is probably the major mechanism of growth promotion of rice by rhizobia. In wetlands, these microorganisms can be great allies in the integration of rice crop with forage legumes. In the scena- rio of rice production of Rio Grande do Sul Brazilian State, most producers use the rice area in the winter with cattle, taking advantage of the rice stubble, or growing ryegrass and some legumes. In this context, during the winter, rhizobia were fixing nitrogen in symbiosis with legumes, promoting the growth of pasture in the summer and come into contact with the rice, colonizing the plant and stimulate its growth and yield. The aim of this review is to record rhizobia as plant growth-promoting bacteria (PGPB) in botanic families such as grasses. It is possible to form soil reservoir of rhizobia in rotation systems with legumes and non-legumes in order to improve the performance of productive systems by means of mechanisms of plantgrowth promotion.