Plant growth-promoting rhizobacteria associated with avocado display antagonistic activity against Phytophthora cinnamomi through volatile emissions

Abstract

Rhizobacteria associated with crops constitute an important source of potentially beneficial microorganisms with plant growth promoting activity or antagonistic effects against phytopathogens. In this study, we evaluated the plant growth promoting activity of 11 bacterial isolates that were obtained from the rhizosphere of healthy avocado trees and from that of avocado trees having survived root rot infestations. Seven bacterial isolates, belonging to the genera Bacillus, Pseudomonas and Arthrobacter, promoted in vitro growth of Arabidopsis thaliana. These isolates were then tested for antagonistic activity against Phytophthora cinnamomi, in direct dual culture assays. Two of those rhizobacterial isolates, obtained from symptomatic-declining trees, displayed antagonistic activity. Isolate A8a, which is closely related to Bacillus acidiceler, was also able to inhibit P. cinnamomi growth in vitro by 76% through the production of volatile compounds. Solid phase microextraction (SPME) and analysis by gas chromatography coupled with mass spectrometry (GC-MS) allowed to tentatively identify the main volatiles emitted by isolate A8a as 2,3,5-trimethylpyrazine, 6,10-dimethyl-5,9-undecadien-2-one and 3-amino-1,3-oxazolidin-2-one. These volatile compounds have been reported to show antifungal activity when produced by other bacterial isolates. These results confirm the significance of rhizobacteria and suggest that these bacteria could be used for biocontrol of soil borne oomycetes through their volatiles emissions.

Characterization of plant growth-promoting bacteria associated with avocado trees (Persea americana Miller) and their potential use in the biocontrol of Scirtothrips perseae (avocado thrips)

“…The identified taxonomic positions have been reported in other studies describing the microbial community of avocado tree soil [51] and the rhizospheres of other Lauraceae species [52]. Recently, Méndez-Bravo et al [15] described seven bacterial isolates of the genera Bacillus, Pseudomonas and Arthrobacter (the old name of several Paenarthrobacter species) with PGPR activity through the production of volatile organic compounds in Arabidopsis seedlings. All these genera were identified in our study.…”

“…Several studies have used the Arabidopsis thaliana plant model to evaluate the beneficial, pathogenic or neutral effects of microorganisms associated with plants and as a rapid system for identifying or characterizing plant growth-promoting bacteria [6][7][8]15,22,41,44,63]. Avocados are large forest trees, often over 20 m tall, that exhibit rhythmic growth with two or more flushes of shoot growth per year, alternating with periods of rest, and that reach optimal yields until five years after planting [42], while A. thaliana completes its life cycle in 8-12 weeks from germination to harvesting.…”

“…Carzola et al [13] reported that four strains of Bacillus subtilis were associated with avocado antifungal activity and showed apparent enzymatic and antibiotic action against phytopathogenic fungi, whereas Guevara-Avendaño et al [14] identified Bacillus strains with the ability to control the phytopathogenic fungi Fusarium euwallaceae and Graphium sp. Méndez-Bravo et al [15] described the effects of Bacillus, Pseudomonas and Arthrobacter isolated from the avocado rhizosphere against Phytophthora cinnamomi through the production of volatile organic compounds.…”

Unravelling the functions of biogenic volatiles in boreal and temperate forest ecosystems

“…Root-associated microbes are involved actively in function of roots (De Coninck et al 2015), and they are capable of emitting BVOCs. Fungal symbionts use their BVOCs to induce mycorrhiza formation (Ditengou et al 2015), and rhizobacteria of several bacterial genera use their BVOCs to protect roots against fungal pathogens (Mendez-Bravo et al 2018). Ectomycorrhiza formation may activate jasmonic acid signalling, alter BVOC profiles and reduce herbivory in foliage of Populus × canescens (Kaling et al 2018).…”

Bark from avocado trees of different geographic locations have consistent microbial communities

“…), a native crop tree from Mexico and Central America, is an economically important commodity in Mexico, as the country has a share of approximately 35% of the worlds production (FAO, 2016;Rendón-Anaya et al 2019). However, avocado production has been hindered by the incidence of several fast-spreading diseases, mostly caused by pathogenic fungi and oomycetes (Méndez-Bravo et al 2018;Guevara-Avendaño et al 2020). Surprisingly, avocado tree bark as a microbial environment has received little attention in the scientific literature, despite being the first point of contact for different pests and diseases.…”