Reduced sensitivity to azoxystrobin is stable in Monilinia fructicola isolates

Abstract

A shift towards declining azoxystrobin sensitivity has been previously documented in a collection of Brazilian Monilinia fructicola isolates, but information on the stability of this trait after in vitro sub-culturing is not available. In this study, one highly-sensitive isolate and two isolates with reduced sensitivity to azoxystrobin, not exhibiting point mutations at codons 129, 137 and 143 in the target gene of cytochrome b were used. Two independent experiments consisted of 10 weekly transfers of each strain in potato dextrose agar (PDA). Conidial production and germination were quantified in the initial culture and, again, after the third, sixth and tenth transfer. Measures of mycelial growth were obtained in colonies growing on PDA amended with azoxystrobin at 1 µg mL −1 and salicylhydroxamic acid at 100 µg mL −1. Data were normalized to mycelial growth rate after each of the 10 transfers. The colony diameter in the less sensitive isolates was stable across the transfers in the PDA amended with the fungicide. The conidial production and mycelial growth rate did not decrease in non-amended media either. Our results suggest that the trait of reduced sensitivity to azoxystrobin is stable under no selection pressure for azoxystrobin.

Fitness costs associated with G461S mutants of Monilinia fructicola could favor the management of tebuconazole resistance in Brazil

“…Conflicting results were also observed on Pyrenophora teres, where resistance to sterol biosynthesis inhibitors (SBI) was not associated with lowered fitness (Peever and Milgroom 1994). In other studies, M. fructicola isolates resistant to dicarboxamides (FRAC#2) were also reported to have lowered fitness (Sanoamuang and Gaunt 1995;Lim et al 2001), but not so for isolates resistant to QoI (FRAC#11) and MBC (FRAC#1) (Penrose et al 1979;Lim et al 1999;Primiano et al 2017).…”

“…In Brazil, the DMI resistance dynamic of M. fructicola is not fully understood. Information on resistance stability and fitness components are only available for isolates from São Paulo with lessened QoI sensitivity, where ten sucessive transfers in-vitro showed no effects on resistance levels, or fitness variables (Primiano et al 2017). In contrary, DMI resistance mechanisms of M. fructicola were recently described in populations from Brazil, and this knowledge plays an important role on resistance dynamics, and potentially to understand whether or not resistance may become stablished within commercial peach orchards in Brazil.…”