Side effects of the sterol biosynthesis inhibitor fungicide, propiconazole, on a beneficial arbuscular mycorrhizal fungus.

Abstract

The Sterol Biosynthesis Inhibitor (SBI) fungicide, propiconazole, is extensively used in modern agriculture to control fungal diseases. Unfortunately, little is known about its potential side effects on non-target plant-beneficial soil organisms such as arbuscular mycorrhizal fungi (AMF). The direct impact of increasing propiconazole concentrations (0.02; 0.2 and 2 mg x L(-1)) on the lipid metabolism of the AMF Glomus irregulare in relation with its development, was studied by using axenic cultures. The propiconazole impact on G. irregulare was investigated, firstly, through sterol (the target-metabolism of SBI fungicides), phospholipids (PL) and their associated fatty acids (PLFA) analysis (the main membrane components) and secondly by measuring malondialdehyde (MDA) (a biomarker of lipid peroxidation) formation. Finally, the storage lipid quantity, triacylglycerol (TAG), was quantified. Our results demonstrated that the drastic reduction of G. irregulare development (germination, germ tube elongation, colonization, extraradical hyphae growth and sporulation) could be explained not only by the decreases of the total sterol end-products (24-methylcholesterol and 24-ethylcholesterol) and by 24-methylene dihydrolanosterol (a sterol precursor) accumulation, suggesting an inhibition of a key enzyme in sterol biosynthesis pathway (14alpha-demethylase), but also by the increases in phosphatidylcholine (PC) and PLFA (C16:0; C18:0 and C18:3) quantities as well as by MDA accumulation. Moreover, TAG quantity was found to be reduced in the presence of propiconazole, suggesting their use by G. irregulare in a response to propiconazole toxicity. In conclusion, taken together, the findings of the current study highlighted a relationship between the SBI fungicide toxicity against the beneficial AMF G. irregulare and (1) the disturbance in the sterol metabolism, (2) the membrane alteration (PC decrease, lipid peroxidation) as well as (3) the reduction in storage lipids, TAG. More generally, this work could contribute to investigate the toxicity of agricultural chemicals on AMF and underlined the emergency of using sustainable alternative method to control plant diseases. Furthermore, these data can provide a useful approach in soil ecotoxicology studies and risk assessment.