Evaluation of polymers for the liquid rhizobial formulation and their influence in the Rhizobium-Cowpea interaction

Abstract

To develop proposals in bacterial formulations applicable to the agricultural sector, a study of physicochemical and biological parameters of the polymeric materials is essential. Here, we evaluated the effects of eight polymers on the cellular viability of Rhizobium sp. G58 during a 2-month period. From these results, we selected the three polymers that yielded the best results in respect to the survival of the bacteria. An assay of the effect of the polymers on the symbiotic activity of Rhizobium-Cowpea and the agronomic parameters was conducted under greenhouse conditions, based on the principal component analysis. A positive effect was found in Rhizobium sp. G58 using the Tukey's Test (p<0.05) with sodium alginate (0.5-1%) and hydroxypropyl methylcellulose-HPMC (0.125-0.5%), while a significant decrease was established in cellular viability using polyethylene glycol-PEG, carbomer-Carbopol 940, and polyvinyl alcohol-PVA. The multivariate analysis indicated that the application of the polymers (sodium alginate and hydroxypropyl methylcellulose) in 0.5% concentration did not have negative effects on the symbiotic fixation of nitrogen or the process of nodulation. In conclusion, our results suggest the effectiveness of these polymers and the possibility of using them as carriers of bacterial formulation without affecting physiological processes.

Polymers selection for a liquid inoculant of Azospirillum brasilense based on the Arrhenius thermodynamic model

“…The viscosity and water holding capacity of these hydrophilic polymers reduced the drying rate and helped to protect cells from environmental stresses. Similar results were obtained with carrageenan on Azotobacter chroococcum (Rojas-Tapias et al, 2015), and alginate with Rhizobium and Bradyrhizobium strains (Tittabutr et al, 2007;Rivera et al, 2014). It is important to establish that these two polymers are used in other type of formulations like microencapsulation, which have been proved to maintain cell viability of nitrogen fixing bacteria for over fourteen years (Bashan and Gonzalez, 1999).…”

“…Bacterial inoculants contain one or more of these beneficial strains in an easy-to-use and economical carrier material (Bashan, 1998), which must be able to maintain the viability of the cells and protect them from the stresses they face once applied into the soil or plant surfaces. There is no universal carrier, and choosing the proper formulation is a strain-specific process as important as the selection of the bacteria itself (Rivera et al, 2014). Solid, liquid, oil and gel based formulations have been developed, each with their own advantages and limitations.…”

Beneficial Microorganisms: Current Challenge to Increase Crop Performance

“…Alternative materials for bacterial inoculation can maintain the quality and efficiency of the inoculum and reduce production costs and negative environmental impacts compared with peat inoculants (Fernandes Júnior et al 2009, 2012Herrmann and Lesueur 2013;Rivera et al 2014). For example, the combination of carboxymethylcellulose (CMC) and starch forms a polymeric carrier that adequately maintains rhizobial cell viability and has the same performance as peat inoculants (Fernandes Júnior et al 2009, 2012.…”

“…3.3). Rhizobial inoculants have been used for many years to obtain greater yields in legumes and are often produced with peat, a material with a fossil origin (Rivera et al 2014). Peat mines are situated in preserved environments where extraction is forbidden, and a lack of natural peat deposits exists in some countries (Albareda et al 2008).…”

Pré-Inoculação de Sementes de Vigna unguiculata (L) Walp. com Inoculante Polimérico no Centro-Oeste

“…Assim como a pré-inoculação em veículo turfoso, onde a nodulação, a massa da parte aérea e o nitrogênio O método tradicional de inoculação de sementes preconiza a semeadura no máximo 24 horas após a aplicação das bactérias nas sementes. Por outro lado, nos últimos anos produtos (FERNANDES JÚNIOR et al, 2009;RIVERA et al, 2014) e práticas (VIEIRA NETO et al, 2008;ZILLI et al, 2010) de inoculação que permitam a inoculação que antecedam este período de 24 horas (pré-inoculação) têm surgido e visam dar agilidade à semeadura no campo. A prática aumentaria o prazo entre a inoculação e o plantio, beneficiando a agricultura empresarial, que necessita de vários dias de plantio em virtude da extensão da área e garantiria a possibilidade de pequenos agricultores de adquirirem sementes já inoculadas.…”