The Role of Volatile Organic Compounds and Rhizosphere Competence in Mode of Action of the Non-pathogenic Fusarium oxysporum FO12 Toward Verticillium Wilt

Abstract

Verticillium wilts caused by Verticillium spp. are among the most challenging plant diseases to control and affect numerous hosts worldwide. Due to the lack of effective, conventional control methods, integrated control strategies provide a promising approach to manage these diseases. The non-pathogenic Fusarium oxysporum strain FO12 was reported in previous studies to be an effective biocontrol agent against Verticillium dahliae , however, its mode of action remains to be elucidated. In this study, complementary in vitro and in vivo experiments were conducted in order to explore the implications of inhibitory substances and rhizosphere competence in antagonistic effects of FO12 against V. dahliae and V. longisporum . Volatile organic compounds and soluble substances produced by FO12, which caused significant inhibition of mycelial growth and microsclerotia viability in the two tested Verticillium species, were identified by means of gas and liquid chromatography-mass spectrometry. We showed that the antagonistic effect of F. oxysporum FO12 is partially due to the production of bioactive compounds such as 3-methyl-1-butanol and 2-methyl-1-butanol, among others. Several metabolic pathways of FO12 were altered upon contact with V. dahliae ELV22 volatiles. The reduced production of alpha, alpha-trehalose, a metabolite used in starch and sucrose metabolism, suggests that the biocontrol agent activates its stress response in the presence of the phytopathogen. Microscopic analysis using sGFP-tagged FO12 on oil seed rape as a model plant suggests that the biocontrol strain is an efficient root colonizer, which could compete with V. dahliae in the same ecological niche. The findings obtained in this study provide new insights into the mode of action of this potential biocontrol agent, which are relevant for controlling Verticillium wilt through an ecologically friendly approach.

Biological Control of Verticillium Wilt on Olive Trees by the Salt-Tolerant Strain Bacillus velezensis XT1

“…However, there are no data available regarding the activity of lipopeptide biosurfactants for B. velezensis OEE1 [ 30 ]. With regard to volatile compounds, they are well known for having antifungal activity, plant growth promoting activity, and inducing systemic resistance [ 73 , 74 , 75 ]. The volatile organic compounds of B. velezensis XT1 inhibited by 34% mycelium growth of V. dahliae , which is comparable to the 40% inhibition reported for B. velezensis OEE1 [ 30 ], although the experimental set up is not exactly the same.…”

Spatiotemporal Dynamics of Maize (Zea mays L.) Root Growth and Its Potential Consequences for the Assembly of the Rhizosphere Microbiota

“…On the other hand, typical rhizosphere microorganisms are often mobile, and bacteria, protists, and some rapidly growing fungi (e.g., “sugar fungi,” de Boer et al, 2006 ) move in parallel to the exudate pulse along the root ( Hünninghaus et al, 2019 ). These organisms are generally characterized by high “rhizosphere competence,” being both, well adapted to fast colonization and fierce competitors for root colonization sites ( Lugtenberg et al, 2001 ; Kamilova et al, 2005 ; Schreiter et al, 2014 , 2018 ; Mulero-Aparicio et al, 2019 ).…”

Verticillium Wilt of Olive and Its Control: What Did We Learn during the Last Decade?

“…Likewise, treatments with conidial suspensions or chlamydospores of FO12 were effective in reducing both the inoculum density of V. dahliae in the soil and the VWO severity [169]. As for the biocontrol mechanism involved, the effect of secondary metabolites produced by FO12 against V. dahliae was investigated [169,170]. In vitro experiments indicated that the metabolites produced by FO12 had little effect on the inhibition of V. dahliae mycelial growth, suggesting that the antagonistic effect relies on the presence of FO12 alive and on a direct interaction with the pathogen [169].…”

“…In addition, the production of VOC by FO12 in the presence of V. dahliae has been reported. Several of these compounds have been previously involved in antifungal activity and biological control [170].…”