Propiconazole Toxicity on the Non-Target Organism, the Arbuscular Mycorrhizal Fungus, Glomus irregulare

Abstract

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts that colonize the roots of most terrestrial plants. Indeed, 80% of vegetal species realize this symbiosis (Bonfante and Perotto, 1995). Plants generally benefit from this AMF association through increased plant nutrient uptake, plant growth and survival rates (Smith and Read, 2008). The symbiotic association may also increase host plant resistance/tolerance against biotic (Hol and Cook, 2005; Akhtar and Siddiqui, 2008) and abiotic stresses, including salinity, drought and pollution (Gerdemann, 1968; Franco-Ramirez et al., 2007; Giri et al., 2007; Sudova et al., 2007; Cartmill et al., 2008; Debiane et al., 2008, 2009; Campagnac et al., 2010). The functioning of AMF may be impaired by cultural practices such as fungicides application (Sukarno et al., 2006). Unfortunately, the use of fungicides is generalized in modern agriculture for the control of fungal diseases. Most of fungicides act directly on essential fungal functions such as respiration, lipid synthesis or cell division (Leroux, 2003). Consequently, they can exhibit undesirable effects on non-target organisms. Among the fungicides, the Sterol Biosynthesis Inhibitor (SBI) family is one of the most used in agriculture (Hewitt, 1998). Four main classes can be distinguished according to their action target site: (i) squalene epoxidation (e.g. naftifine, terbinafine, tolnaftate), (ii) Δ14 demethylation or DMIs (e.g. imazalil, prochloraz, triadimenol, propiconazole), (iii) Δ14reduction and/or Δ8→ Δ7 isomerisation (e.g. fenpropidine, fenpropimorph, tridemorph), (iiii) C4 demethylation (e.g. fenhexamid) (Leroux, 2003). Several studies carried out on SBI fungicide impact on mycorrhizal plants showed contradictory results on the plant growth, on AM fungal development and on the symbiosis functioning (Dodd and Jeffries, 1989; Von Alten et al., 1993; Schweiger and Jacobsen, 1998; Kjoller and Rosendahl, 2000; Schweiger et al., 2001). The use of different experimental procedure in the reported studies (plant species, culture conditions, fungicide formulation, application methods...) did not allow easy comparison with the results obtained and led to some difficulties to give clear conclusion concerning the SBI fungicides effect on AMF (Sancholle et al., 2001).