Instability of Propiconazole Resistance and Fitness in Monilinia fructicola

Abstract

The fitness and the dynamics of demethylation inhibitor fungicide (DMI) sensitivity in isolates of Monilinia fructicola sensitive (no growth at 0.3 mg/liter propiconazole) and resistant (>/=50% relative growth at 0.3 mg/liter propiconazole) to propiconazole were investigated. Overall, there was no considerable compromise in the fitness of resistant isolates compared to sensitive isolates of M. fructicola at the time of collection. Resistant and sensitive isolates differed in their sensitivity to propiconazole (P < 0.001) and incubation period (P = 0.044), but not in latent period, growth rate, spore production, and spore germination frequency (P > 0.05). Consecutive transferring on potato dextrose agar had an impact on conidia production, conidial germination, and growth rate (P < 0.0001). Consecutive transferring also had an impact on propiconazole sensitivity in resistant isolates. In the resistant isolates, sensitivity to propiconazole increased (R(2) = 0.960, P = 0.0034) within the first eight transfers. Similarly, sensitivity to propiconazole increased by 273% over the course of 34 months in cold storage in propiconazole-resistant isolates. Our results show that propiconazole resistance is unstable in vitro and that standard subculturing and cold storage procedures impact propiconazole sensitivity of resistant isolates. The instability of propiconazole resistance in M. fructicola may have important implications for disease management in that a reversion to propiconazole sensitivity could potentially occur in the absence of DMI fungicide pressure in the field.

Reduced sensitivity to azoxystrobin is stable in Monilinia fructicola isolates

“…There is a high degree of variability in conidia production and usually the number of conidia shows linear and gradual changes between transfers (Cox et al, 2007;Fan et al, 2015;Laleve et al, 2014;Vega and Dewdney, 2014). This high variability has also been observed in M. fructicola isolates with reduced sensitivity to propiconazole (Cox et al, 2007).…”

“…There is a high degree of variability in conidia production and usually the number of conidia shows linear and gradual changes between transfers (Cox et al, 2007;Fan et al, 2015;Laleve et al, 2014;Vega and Dewdney, 2014). This high variability has also been observed in M. fructicola isolates with reduced sensitivity to propiconazole (Cox et al, 2007). In most studies on QoI-resistant fungi, pathogens with a mutation at codon 143 showed, qualitatively, stable resistance following successive transfers in non-amended media, such as in azoxystrobin-resistant Magnaporthe grisea (Avila-Adame and Koller, 2003), Didymella bryoniae isolates (Finger et al, 2013) and pyraclostrobin-resistant Venturia inaequalis isolates (Frederick et al, 2014).…”

“…The intensive use of these fungicides selects for resistance to triazoles and reduced-sensitivity to azoxystrobin in M. fructicola isolates (May De Mio et al, 2011). Resistance instability has been reported for M. fructicola isolates with reduced sensitivity to propiconazole without a corresponding point mutation in the cytochrome P450 sterol 14α-demythylase gene (CYP51) (Cox et al, 2007). The levels of sensitivity to propiconazole increased in M. fructicola isolates after successive transfers in vitro and under different storage procedures, such as glycerol, filter paper, mineral oil and silica gel at low or ultralow temperatures (Cox et al, 2007;Zhu et al, 2012).…”

“…Resistance instability has been reported for M. fructicola isolates with reduced sensitivity to propiconazole without a corresponding point mutation in the cytochrome P450 sterol 14α-demythylase gene (CYP51) (Cox et al, 2007). The levels of sensitivity to propiconazole increased in M. fructicola isolates after successive transfers in vitro and under different storage procedures, such as glycerol, filter paper, mineral oil and silica gel at low or ultralow temperatures (Cox et al, 2007;Zhu et al, 2012). Two azoxystrobin-resistant M. fructicola isolates, without point mutation in the target gene cytochrome b (cyt b), were detected in China and exhibited similar behavior with increased sensitivity to the fungicide after five transfers.…”

“…Information about the stability of reduced sensitivity to azoxystrobin in M. fructicola is important for both methodological and practical issues (Koller et al, 1991). While a decreasing sensitivity in the population could lead to increasing doses of fungicides, potential loss of resistance upon continuous fungus transfer in non-amended media should be considered in resistance and fitness studies (Cox et al, 2007).…”