TAG finds fungicide-resistant Septoria tritici in UK

The Arable Group (TAG) has been monitoring DMI (including the triazoles)
resistant phenotypes (the observable physical or biochemical characteristics of
an organism, as determined by both genetic makeup and environmental influences)
of Septoria tritici for the last three seasons, with samples from key trial
treatments being analysed by the French agricultural research body, INRA.

The situation over the last few years has been one of relative stability in
triazole performance and the composition of S. tritici populations have been
dominated by those phenotypes that are classified as ‘moderately resistant’ to
DMI fungicides. However, in June this year INRA announced that it found in 2008
for the first time a phenotype classified as ‘highly resistant’ in samples taken
in France.

In laboratory tests this more highly resistant phenotype required 2.5 to 10
times the dose of key DMI fungicides that the moderately resistant phenotypes
required, in order to achieve similar levels of control. These highly resistant
phenotypes were not present in the samples from the UK submitted by TAG in 2008.

In July 2009 TAG took samples from three areas in England: Gloucestershire,
Lincolnshire and Norfolk, and sent them to INRA. One sample taken in
Lincolnshire was found to contain the more highly resistant phenotype at a
relatively low proportion of the population.

The implications of this occurrence are not yet clear and there are many
questions to be answered. The potential impact of these more highly resistant
phenotypes on field performance is not known, nor at this stage whether these
phenotypes are sufficiently ‘fit’ to become dominant in field populations.

This development is of potential concern and more research and monitoring is
required. TAG will update its members as and when more information becomes
available.