Unconventional Yeasts Are Tolerant to Common Antifungals, and Aureobasidium pullulans Has Low Baseline Sensitivity to Captan, Cyprodinil, and Difenoconazole

Abstract

Many yeasts have demonstrated intrinsic insensitivity to certain antifungal agents. Unlike the fungicide resistance of medically relevant yeasts, which is highly undesirable, intrinsic insensitivity to fungicides in antagonistic yeasts intended for use as biocontrol agents may be of great value. Understanding how frequently tolerance exists in naturally occurring yeasts and their underlying molecular mechanisms is important for exploring the potential of biocontrol yeasts and fungicide combinations for plant protection. Here, yeasts were isolated from various environmental samples in the presence of different fungicides (or without fungicide as a control) and identified by sequencing the internal transcribed spacer (ITS) region or through matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Among 376 isolates, 47 taxa were identified, and Aureobasidium pullulans was the most frequently isolated yeast. The baseline sensitivity of this yeast was established for 30 isolates from different environmental samples in vitro to captan, cyprodinil, and difenoconazole. For these isolates, the baseline minimum inhibitory concentration (MIC50) values for all the fungicides were higher than the concentrations used for the control of plant pathogenic fungi. For some isolates, there was no growth inhibition at concentrations as high as 300 µg/mL for captan and 128 µg/mL for cyprodinil. This information provides insight into the presence of resistance among naturally occurring yeasts and allows the choice of strains for further mechanistic analyses and the assessment of A. pullulans for novel applications in combination with chemical agents and as part of integrated plant-protection strategies.

Biological Control of Aspergillus flavus by the Yeast Aureobasidium pullulans In Vitro and on Tomato Fruit

“…In order to achieve such a purpose while maintaining adequate efficacy, a good way is to combine chemical fungicides with a biocontrol agent. The microbial biocontrol agent approach to tomato disease management is ecologically safe and capable of hindering or defeating pathogen populations [ 10 , 15 , 20 ]. Among the microorganisms antagonistic to plant pathogens, yeast meets many conditions for an effective biocontrol agent.…”

“…A. pullulans is one of the most common inhabitants of the phyllosphere of many crop plants and is also found in many other habitats [ 35 ]. These yeasts can also thrive in various environmental conditions (e.g., hypersaline habitats, arid conditions, glaciers, and radiation sites) due to the presence of genes involved in stress tolerance [ 20 ]. The presented study examined the various aspects of polyextremotolerance of the tested strains of A. pullulans , including tolerance to low and high temperatures, pH, and salinity.…”

“…The authors observed a mutation in the CYTb gene (G143A) in the azoxystrobin-resistant yeast A. pullulans . Magoye et al [ 20 ] showed that the baseline minimum inhibitory concentration (MIC50) values determined for 30 different strains of A. pullulans and 3 fungicides, such as captan, cyprodinil, and difenoconazole, were higher than the concentrations of the respective fungicides used under field conditions to control plant pathogens.…”

“…We suspect this may have significantly affected the tolerance of the strains A. pullulans PP4 and A. pullulans ZD1 against the tested agrochemicals. Magoye et al [ 20 ] suggest that this yeast exhibits a rather pleiotropic mechanism of tolerance to fungicides instead of a specific resistance mechanism to a particular agent. The study presented in this paper and a report by other authors [ 20 ] indicate that high abundance in the environment, competitiveness, and stress tolerance are associated with low sensitivity to antifungal agents.…”

Stability of Dry and Liquid Metschnikowia pulcherrima Formulations for Biocontrol Applications against Apple Postharvest Diseases

“…(APC 1.2; CCOS984), Pichia kluyveri (APC 11.10B; CCOS982), and Wickerhamomyces anomalus (SCH 5.6). All isolates were obtained from Swiss agricultural samples and used in previous studies [2,4,30,31]. For competition assays, an isolate of Gibberella fujikuroi (BC 8.14, CCOS1020, SH213620.07FU), obtained from an agricultural soil sample, was used as a model.…”