Diffusible and volatile organic compounds produced by avocado rhizobacteria exhibit antifungal effects against Fusarium kuroshium

Abstract

Rhizobacteria emit bioactive metabolites with antifungal properties that could be used for biocontrol of fungal diseases. In this study, we evaluated the potential of diffusible and volatile organic compounds (VOCs) emitted by avocado rhizobacteria to inhibit the growth of Fusarium kuroshium, one of the causal agents of Fusarium dieback (FD) in avocado. Three bacterial isolates (INECOL-6004, INECOL-6005, and INECOL-6006), belonging to the Bacillus genus, were selected based on their capacity to inhibit several avocado fungal pathogens, and tested in antagonism assays against F. kuroshium. The three bacterial isolates significantly inhibited F. kuroshium mycelial growth by up to 48%. The composition of bacterial diffusible compounds was characterized by the analysis of EtOAc and n-BuOH extracts by using ultra-performance liquid chromatography (UPLC) coupled to high-resolution mass spectrometry (HRMS). The three bacterial isolates produced cyclo-lipopeptides belonging to the iturin, fengycin, and surfactin families. The antifungal activity of n-BuOH extracts was larger than that of EtOAc extracts, probably due to the greater relative abundance of fengycin in the former than in the latter. In addition, isolates INECOL-6004 and INECOL-6006 significantly inhibited F. kuroshium mycelial growth through VOC emission by up to 69.88%. The analysis of their VOC profiles by solid phase micro-extraction (SPME) coupled to gas chromatography and mass spectrometry (GC-MS) revealed the presence of ketones and pyrazine compounds, particularly of 2-nonanone, which was not detected in the VOC profile of isolate INECOL-6005. These results emphasize the need to further investigate the antifungal activity of each bioactive compound for the development of new formulations against fungal phytopathogens.

Phytophthora Root Rot Modifies the Composition of the Avocado Rhizosphere Microbiome and Increases the Abundance of Opportunistic Fungal Pathogens

“…Samples of rhizosphere soil of avocado were collected from the orchard San Carlos in Huatusco, Veracruz, as described in our previous studies ( Méndez-Bravo et al, 2018 ; Guevara-Avendaño et al, 2020 ). A map of the orchard was provided in Méndez-Bravo et al (2018) .…”

“…Our previous studies have allowed us to identify microorganisms associated with root rot symptomatic and asymptomatic avocado trees with beneficial functions, such as pathogen-antagonistic and plant growth-promoting activities ( Méndez-Bravo et al, 2018 ; Guevara-Avendaño et al, 2020 ). We have previously isolated and characterized bacterial strains with the ability to antagonize several avocado pathogens ( Guevara-Avendaño et al, 2020 ) and to promote plant growth in vitro ( Méndez-Bravo et al, 2018 ) by sampling an orchard with a high relative humidity in Veracruz State, Mexico. The objective of the present study was thus to characterize the impact of avocado root rot on the assembly of rhizosphere microbial community and predict shifts in their potential functions, using 16S ribosomal DNA (rDNA) and internal transcribed spacer (ITS) amplicon sequencing.…”

Microbial Biocontrol Strategies for Ambrosia Beetles and Their Associated Phytopathogenic Fungi

“…compounds from the iturin and surfactin families, which have been previously described for their antifungal activities (Malfanova et al, 2012;Torres et al, 2017;Théatre et al, 2021). The inhibition of F. kuroshium by Bacillus natural products was further reported by Guevara-Avendaño et al (2020) and Báez-Vallejo et al (2020). In both studies, the analysis of bacterial extracts by ultra-performance liquid chromatography coupled to high-resolution mass spectrometry revealed the presence of cyclic lipopeptides from the iturin, surfactin, and fengycin families (Table 2) as the putative antifungal compounds.…”

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.…”