Impact of antifungals producing rhizobacteria on the performance of Vigna radiata in the presence of arbuscular mycorrhizal fungi

Abstract

Plant growth-promoting rhizobacteria (PGPR) that produce antifungal metabolites are potential threats for the arbuscular mycorrhizal (AM) fungi known for their beneficial symbiosis with plants that is crucially important for low-input sustainable agriculture. To address this issue, we used a compartmented container system where test plants, Vigna radiata, could only reach a separate nutrient-rich compartment indirectly via the hyphae of AM fungi associated with their roots. In this system, where plants depended on nutrient uptake via AM symbiosis, we explored the impact of various PGPR. Plants were inoculated with or without a consortium of four species of AM fungi (Glomus coronatum, Glomus etunicatum, Glomus constrictum, and Glomus intraradices), and one or more of the following PGPR strains: phenazine producing (P(+)) and phenazine-less mutant (P(-)), diacetylphloroglucinol (DAPG) producing (G(+)) and DAPG-less mutant (G(-)) strains of Pseudomonas fluorescens, and an unknown antifungal metabolite-producing Alcaligenes faecalis strain, SLHRE425 (D). PGPR exerted only a small if any effect on the performance of AM symbiosis. G(+) enhanced AM root colonization and had positive effects on shoot growth and nitrogen content when added alone, but not in combination with P(+). D negatively influenced AM root colonization, but did not affect nutrient acquisition. Principal component analysis of all treatments indicated correlation between root weight, shoot weight, and nutrient uptake by AM fungus. The results indicate that antifungal metabolites producing PGPR do not necessarily interfere with AM symbiosis and may even promote it thus carefully chosen combinations of such bioinoculants could lead to better plant growth.

Specificity of plant-microbe interactions in the tree mycorrhizosphere biome and consequences for soil C cycling

“…AM have also been found to alter the structure of mycorrhizosphere microbial communities (Rillig and Mummey, 2006; Toljander et al, 2007; Welc et al, 2012). Isolation and identification of rhizobacteria found in the mycorrhizosphere around AM hyphae have shown bacteria with antagonistic properties toward soil-borne pathogens (Lioussanne et al, 2010), and antifungal properties (although they do not affect the AM symbiosis; Dwivedi et al, 2009). The N 2 fixing ability of some AM plants improves when mycorrhizae are present vs. when they are absent (Kucey and Paul, 1982; Fitter and Garbaye, 1994).…”

Manipulation of rhizosphere organisms to enhance glomalin production and C sequestration: Pitfalls and promises

“…Some PGPR produce phytohormones that enhance AMF colonization by increasing root surface area and susceptibility of the plant to AMF hyphae penetration Barea et al 2002;Dwivedi et al 2009). Other PGPR inhibit the growth of pathogens that interfere with AM fungal symbiotic association with plants (Vessey 2003).…”

Synergistic effect of arbuscular mycorrhizal fungi and Bacillus subtilis on the biomass and essential oil yield of rose-scented geranium (Pelargonium graveolens)

“…This indicates that nutrient uptake increases concomitantly with better mycorrhizal colonization. AM colonization was greatly stimulated by PGPR inoculation, which in turn greatly affected the shoot biomass, leaf/stem (L/S) ratio and uptake of major nutrients, including P. The production of metabolites involved in increasing root cell permeability and hormone synthesis by the PGPR is the mechanism expected to be involved in increasing AM colonization (Duponnois and Plenchette 2003;Dwivedi et al 2009). Many soil microorganisms are able to solublize phosphate ions from sparingly soluble inorganic or organic P compounds in vitro (Hameeda et al 2008).…”