Annual ryegrass-associated bacteria with potential for plant growth promotion

Abstract

Annual ryegrass is a fast-growing cool-season grass broadly present in the Portuguese "montado", a typically Mediterranean agro-forestry-pastoral ecosystem. A culture-dependent approach was used to investigate natural associations of this crop with potentially beneficial bacteria, aiming to identify strains suitable for biofertilization purposes. Annual ryegrass seedlings were used to trap bacteria from three different soils in laboratory conditions. Using a nitrogen-free microaerophilic medium, 147 isolates were recovered from the rhizosphere, rhizoplane, and surface-sterilized plant tissues, which were assigned to 12 genera in classes Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Bacilli and Actinobacteria. All isolates were able to grow in the absence of nitrogen and several of them were able to perform in vitro activities related to plant growth promotion. Isolates of the genera Sphingomonas and Achromobacter were found to be the most effective stimulators of annual ryegrass growth under nitrogen limitation (47-92% biomass increases). Major enhancements were obtained with isolates G3Dc4 (Achromobacter sp.) and G2Ac10 (Sphingomonas sp.). The latest isolate was also able to increment plant growth in nitrogen-supplemented medium, as well as the phosphate solubilizer and siderophore producer, G1Dc10 (Pseudomonas sp.), and the cellulose/pectin hydrolyser, G3Ac9 (Paenibacillus sp.). This study represents the first survey of annual ryegrass-associated bacteria in the "montado" ecosystem and unveiled a set of strains with potential for use as inoculants.

Diazotrophic potential among bacterial communities associated with wild and cultivatedAgavespecies

“…However, data clustering was not as clear as in the epiphytic communities. This finding is similar to studies in the gramineae Lolium multiflorum (Castanheira et al, 2014) where the same taxa were isolated too. The endosphere of the wild A. salmiana was dominated by a single OTU, the a-Proteobacteria: Reyranella (OTU 68), a novel genus with only three species described to date (Pagnier et al, 2011;Kim et al, 2013;Lee & Whang, 2014).…”

Plant growth-promoting Burkholderia species isolated from annual ryegrass in Portuguese soils

“…In both assays the size of haloes around colonies was measured as described in Castanheira et al . ().…”

“…Inoculation experiments of Lolium multiflorum were performed in a controlled‐environment chamber using the procedures reported by Castanheira et al . (). A modified Evans medium (Evans et al .…”

Isolation of N2‐fixing rhizobacteria from Lolium perenne and evaluating their plant growth promoting traits

“…Despite its interest as a forage grass, information on plant‐associated beneficial bacteria in the rhizosphere of L. perenne is scarce. Although utilization of synthetic N‐fertilizers for plant growth is a common agricultural practice, excess nitrate addition has resulted in unacceptable levels of waters, soils, sediments, and atmospheric pollution .…”