QoI resistance is that
the G143A mutation seems to incur no fitness cost to
the fungus (Gisi et al. 2002). Therefore, a pathogen
population gaining QoI resistance through a selective
sweep imposed by applications of QoI fungicide is
likely to maintain the resistance even after fungicide
application is reduced or stopped entirely.
The emergence and rapid increase in frequency of
QoI-resistant haplotypes was already reported in
Western Europe (Fraaije et al. 2005). The resistance
emerged independently in different genetic backgrounds
and geographical regions and spread rapidly
through wind dispersal of ascospores (Torriani et al.
2009). The historic asymmetric gene flow from
Western Europe may have introduced QoI-resistant
alleles into Czech populations. The significant levels
of gene flow among populations in the Czech
Republic would likely have contributed to the rapid
subsequent spread of QoI resistance to the different
regions once QoI resistance was established in the
Czech Republic. However, two factors suggest that
QoI resistance may have independently arisen in the
Czech Republic. First, recent gene flow was more
constrained between Western Europe and the Czech
Republic, making it less likely that QoI-resistant
alleles spread quickly from neighbouring countries.
Second, the QoI-resistant alleles were first detected
in the central region of the Czech Republic (locations
III and V) and subsequently found in the neighbouring
location I. This suggests that QoI resistance may have
emerged and spread from the centre of the Czech
Republic to the periphery. However, our collections
do not contain isolates from all locations from the
earlier sampling years and we may have missed some
earlier emergence of QoI resistance. The current fungicide
application strategy for Czech wheat fields consists
of 1-2 applications of a combination of azoles and
QoI fungicides (Jan Kazda, pers. comm.). However,
the rapid emergence of QoI resistance casts doubt on