Bacteria-Inducing Legume Nodules Involved in the Improvement of Plant Growth, Health and Nutrition

Abstract

Bacteria-inducing legume nodules are known as rhizobia and belong to the class Alphaproteobacteria and Betaproteobacteria. They promote the growth and nutrition of their respective legume hosts through atmospheric nitrogen fixation which takes place in the nodules induced in their roots or stems. In addition, rhizobia have other plant growth-promoting mechanisms, mainly solubilization of phosphate and production of indoleacetic acid, ACC deaminase and siderophores. Some of these mechanisms have been reported for strains of rhizobia which are also able to promote the growth of several nonlegumes, such as cereals, oilseeds and vegetables. Less studied are the mechanisms that have the rhizobia to promote the plant health; however, these bacteria are able to exert biocontrol of some phytopathogens and to induce the plant resistance. In this chapter, we revised the available data about the ability of the legume noduleinducing bacteria for improving the plant growth, health and nutrition of both legumes and nonlegumes. These data showed that rhizobia meet all the requirements of sustainable agriculture to be used as bio-inoculants allowing the total or partial replacement of chemicals used for fertilization or protection of crops.

Analysis of the Interaction between Pisum sativum L. and Rhizobium laguerreae Strains Nodulating This Legume in Northwest Spain

“…The ability to fix nitrogen in symbiosis with legumes was the first plant growth promotion mechanism studied in members of the genus Rhizobium [ 41 ], but other mechanisms have been more recently reported, such as the ability to solubilize phosphate, to synthesize indole acetic acid, or to produce siderophores [ 42 ]. In this work, we analyzed these mechanisms in selected strains from each RAPD group showing that all of them produced IAA and siderophores, but only two of them were able to solubilize phosphate ( Table 1 ).…”

Plant Growth Promotion Abilities of Phylogenetically Diverse Mesorhizobium Strains: Effect in the Root Colonization and Development of Tomato Seedlings

“…The capacity of species from genus Mesorhizobium to fix atmospheric nitrogen in symbiosis with legumes is widely known [68]; nevertheless, the presence of other in vitro plant growth promoting mechanisms has been less studied [12,19]. Among these mechanisms, IAA production is one of the most widespread PGP traits among Mesorhizobium strains [19] and this finding has been confirmed in this study, where the levels of IAA produced by some strains, particularly M. ciceri CCANP14 and M. tamadayense CCANP122 are similar to those found in Rhizobium strains able to promote the tomato growth [14].…”

“…Most of these mechanisms have been reported for rhizobia belonging to different genera and families [10][11][12]. In addition to their ability to fix atmospheric nitrogen with legumes [13], the production of the auxin IAA is probably the most common direct mechanism observed in strains from genera Rhizobium [14][15][16], Phyllobacterium [17] and Mesorhizobium [18,19], which can also synthesize and secrete siderophores [14][15][16]19].…”

Rhizobium Presence and Functions in Microbiomes of Non-leguminous Plants

“…Member of this genus is able to interact and produce benefits in a wide range of crops, such as the most important grain food crops, including rice, maize, wheat, and barley; vegetable crops, including lettuce, carrots, potatoes, and spinach; or bioenergy crops, such as canola, sunflower, or switchgrass. The functions and properties that Rhizobium exert in Non-leguminous plants, especially the ones related to plant growth promotion, are extensively reviewed in the last years (Vargas et al 2017;Nag et al 2019;Yoneyama et al 2019;Velázquez et al 2019;Mahmud et al 2020). The involvement of Rhizobium in biocontrol actions against pathogens an alleviation of stresses is a not well-studied characteristic; however, there are some studies showing the potential of this feature; for example, Bellabarba et al (2019) reviewed the importance of plant growth-promoting rhizobia in the alleviation of salt and osmotic stresses as well as in contaminated soils.…”