Baseline Sensitivity of Monilinia fructicola from China to the DMI Fungicide SYP-Z048 and Analysis of DMI-Resistant Mutants

Abstract

Sterol 14α-demethylase inhibitors (DMIs) continue to be important in the management of brown rot of Monilinia spp. worldwide. In this study, the sensitivity of 100 Monilinia fructicola isolates from four unsprayed orchards and two packinghouses in Beijing, China, to the new DMI fungicide SYP-Z048 was evaluated and ranged from 0.003 to 0.039 and 0.016 to 0.047 μg/ml, respectively. Laboratory mutants resistant to SYP-Z048 were generated using UV irradiation but no mutants occurred spontaneously. Resistance was stable after 10 weekly consecutive transfers on fungicide-free medium. Three parameters, including growth rate, sporulation in vitro, and lesion area, were significantly different when sensitive isolates and resistant mutants were analyzed as groups. Mutants grew more slowly and developed significantly smaller lesions on detached fruit, and their sporulation ability in vitro was reduced. Cross resistance was found between SYP-Z048 and propiconazole (ρ = 0.82, P < 0.0001) but not between SYPZ048 and tridemorph, carbendazim, procymidone, azoxystrobin, or pyrimethanil. SYP-Z048 resistance in mutants exhibiting 50% mycelial growth inhibition values greater than 0.3 μg/ml was correlated with the presence of a mutation in the CYP51 gene that encodes the target protein for DMI fungicides. The mutation caused an amino acid change from tyrosine to phenylalanine at position 136 (Y136F). To our knowledge, this is the first baseline sensitivity of M. fructicola collected from China to a DMI fungicide. The inability of M. fructicola to generate spontaneous DMI-resistant mutants coupled with reduced fitness of Y136F mutants can explain why this target site mutation has not yet emerged as a DMI fungicide resistance determinant in M. fructicola field populations worldwide.

Sensitivity of Fusarium graminearum causing head blight of wheat in Brazil to tebuconazole and metconazole fungicides

“…The sensitivity determined in this study constitutes a critical step for monitoring temporal and spatial changes in EC 50 and identification of risk factors related to management practices leading to decline in sensitivity (Chen et al, 2012). The cross-resistance detected in our study suggests similarities in the mode of action between tebuconazole and metconazole (Karaoglanidis & Thanassoulopoulos, 2003).…”

“…As discussed by Klix et al (2007), the decline in the sensitivity to triazoles of F. graminearum owing to selection is not generally considered a key determinant of the relatively low fungicide efficacy against FHB under field conditions. However, it is well known from the literature that failures in disease control have been associated with the decline in sensitivity of other important pathogens such as Monilinia fructicola (Chen et al, 2012), Venturia inaequalis (Pfeufer & Ngugi, 2012) and Mycosphaerella graminicola (Leroux et al, 2007) due to indiscriminate use of triazoles.…”

“…Bartlett test was used to assess variance homoscedasticity and the data from the two experiments were combined (P < 0.05) for analysis (Chen et al, 2012).…”

Fungicide-induced transposon movement in Monilinia fructicola

“…For all isolates, DNA was extracted from mycelium using a modified Cetyl Trimethylammonium Bromide method (Chen et al, 2012). Spores were scraped off the surface of a 7-day-old culture grown on tomato sauce agar (227 g canned tomato sauce with no additives and 20 g agar in 750 ml water) and placed into 2-ml centrifuge tubes containing 1000 μl sterile water.…”

“…The mechanism of lethal exposure to azoxystrobin is likely due to lack of ATP production in combination with excessive ROS production that directly causes damage to DNA, RNA, and proteins, however the effects of continuous exposure to sublethal doses of azoxystrobin is unknown. The action of the DMI fungicide SYP-Z048 (Chen et al, 2012) is by inhibition of sterol 14a-demethylase (CYP51), a cytochrome P450 required for biosynthesis of sterols of fungal cell membranes. Most DMIs bind to the active site of the cytochrome P450 (Siegel, 1981).…”