Plant growth-promoting mechanisms and genetic diversity of bacteria strains isolated from Brachiaria humidicola and Brachiaria decumbens.

João T.C Oliveira,Everthon F Figueredo,Adijailton J Souza,Júlia Kuklinsky-Sobral,Williane P.S Diniz,Fernando J Freire,Arthur P.A Pereira,Gilka T Silva

doi:10.1590/0001-3765202120191123

Abstract

Plant growth-promoting bacteria (PGPB) have received great interest in recent decades. However, PGPB mechanisms remain poorly understood in forage species. We aimed to evaluate roots endophytic and rhizospheric bacteria strains from Brachiaria humidicola and Brachiaria decumbens. The strains were evaluated for biological nitrogen-fixing in saline stress (0 to 10.0 g L-1 of NaCl), N-acyl homoserine lactones and indole-like compounds (ILC) production, the activity of hydrolytic enzymes, and inorganic phosphate solubilization (IPS) under different C sources. The diversity of strains was assessed by BOX-PCR. About 58% of strains were positive for BNF. High salinity levels reduced the growth and BNF. About 58% produced N-acyl homoserine lactones. The ILC was present in 39% of strains. Cellulase, polygalacturonase, pectate lyase, and amylase production were observed in 77, 14, 22, and 25% of strains, respectively. The IPS was observed in 44, 81, and 87% of isolates when glucose, mannitol and sucrose were used, respectively. Comparing two plant species and niches, the strains associated with B. humidicola and root endophytic presented more PGPB mechanisms than others. We found high strain diversity, of which 64% showed similarity lower than 70%. These results can be supporting the bioproducts development to increase forage grasses production in tropical soils.

Highlights

The forage grasses have a primordial importance to worldwide livestock (Capstaff & Miller 2018), mainly to Brazilian production chain because the meat and milk production is an almost exclusively pasture-based system (Cerri et al 2016)
In Brazil, there is a wide diversity of the tropical forage grasses which can be used as pasture (Aguiar et al 2017)
The experiment consisted for 18 bacterial strains isolated from Brachiaria humidicola (Rendle) Schweickerdt and 18 bacterial isolated from Brachiaria decumbens Stapf, being nine root endophytic strains and nine rhizospheric strains per forage grass

Summary

Introduction

The forage grasses have a primordial importance to worldwide livestock (Capstaff & Miller 2018), mainly to Brazilian production chain because the meat and milk production is an almost exclusively pasture-based system (Cerri et al 2016). In Brazil, there is a wide diversity of the tropical forage grasses which can be used as pasture (Aguiar et al 2017). Comprises about 114 million hectares of the pasture in Brazil. Germain & Evrard) Crins (ruzigrass) are the main pasture varieties present in the country (Rezende et al 2017, Souza et al 2018). The use of Brachiaria spp. grasses for pasture formation was possible due to their high adaptability and tolerance to different soil types and climatic conditions, as well as their easier and more

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