Plant growth-promoting rhizobacteria for improving nodulation and nitrogen fixation in the common bean (Phaseolus vulgaris L.)

Abstract

A greenhouse experiment was performed to evaluate the effects of plant growth-promoting rhizobacteria (PGPR) on nodulation, biological nitrogen fixation (BNF) and growth of the common bean (Phaseolus vulgaris L. cv. Tenderlake). Single and dual inoculation treatments of bean with Rhizobium and/or PGPR were administered to detect possible changes in the levels of and interactions between the phytohormones IAA and cytokinin. Bean plants cv. Tenderlake were grown in pots containing Fluvic Neosol eutrophic (pH 6.5). Fourteen kilogram aliquots of soil contained in 15-l pots were autoclaved. Bean seeds were surface sterilized and inoculated with Rhizobium tropici (CIAT 899-standard strain) alone and in combination with one of the PGPR strains: Bacillus endophyticus (DSM 13796), B. pumilus (DSM 27), B. subtilis (DSM 704), Paenibacillus lautus (DSM 13411), P. macerans (DSM 24), P. polymyxa (DSM 36), P. polymyxa (Loutit L.) or Bacillus sp.(65E180). The experimental design was randomized block design with three replications. Beans co-inoculated with Rhizobium tropici (CIAT899) and Paenibacillus polymyxa (DSM 36) had higher leghemoglobin concentrations, nitrogenase activity and N 2 fixation efficiency and thereby formed associations of greater symbiotic efficiency. Inoculation with Rhizobium and P. polymyxa strain Loutit (L) stimulated nodulation as well as nitrogen fixation. PGPR also stimulated specific-nodulation (number of nodules per gram of root dry weight) increases that translated into higher levels of accumulated nitrogen. The activities of phytohormones depended on their content and interactions with Rhizobium tropici and Paenibacillus and/or Bacillus (PGPR) strains which affect the cytokinin in content in the common bean.

Technical and economic viability of co-inoculation with Azospirillum brasilense in soybean cultivars in the Cerrado

“…Due to the high N requirement of the crop (estimated to be 80 kg of N to produce 1000 kg of soybean grains) to obtain high yields, N 2 fixation must work with maximum efficiency (Figueiredo et al, 2008;Vieira Neto et al, 2008;Zilli et al, 2008;Hungria et al, 2010;Rodrigues et al, 2012;Bulegon et al, 2016). Considering the main current and potential limitations of BNF in the soybean crop and the benefits caused in various crops by the inoculation with Azospirillum (free-living diazotrophic bacteria), especially greater root system development and, consequently, higher absorption of water and nutrients, it can be deduced that joint co-inoculation of bradyrhizobia and Azospirillum can enhance crop performance, in an approach that respects the current demands for agricultural, economic, social and environmental sustainability (Hungria et al, 2013).…”

Modes of application of cobalt, molybdenum and Azospirillum brasilense on soybean yield and profitability

“…Due to the large nitrogen (N) requirement by the crops to achieve high yields, N 2 fixation must function with maximum efficiency (Figueiredo et al, 2008;Vieira Neto et al, 2008;Zilli et al, 2008;Hungria et al, 2010;Rodrigues et al, 2012;Ignácio et al, 2015;Bulegon et al, 2016). Besides using inoculant with Bradyrhizobium selected and efficient, cobalt (Co) and molybdenum (Mo) decisively contribute to the biological N 2 fixation (BNF) (Dourado Neto et al, 2012), influencing the synthesis of leghemoglobin, which determines the activity of the nodules and, being a structural component of the nitrogenase, catalyzes the reduction of atmospheric N 2 to NH 3 (Bárbaro et al, 2009a;Golo et al, 2009).…”

Inoculation with Bradyrhizobium sp. and Azospirillum brasilense Associated with Application of Cobalt and Molybdenum on Nutrition and Soybean Yield

“…It is estimated that 80 kg of N is needed to produce 1000 kg of soybean grains. Therefore, to obtain high yields, the biological fixation of N 2 (BNF) should be as efficient as possible [2][3][4][5][6][7].…”