It is now known that there are a large number of mutations (<27 different mutations, deletions or substitutions) in the sterol 14 alpha-demethylase protein (CYP51) in S. tritici that can affect the sensitivity of S. tritici to azole fungicides. The variability in performance of some of the less-effective products may be linked to specific genetic mutations that are now present in local S. tritici populations.
The variation in performance of any azole from site to site may be related to the level of key mutations in the S. tritici population, particularly the I381V mutation, which appears to be one of the key mutations affecting performance of the azole fungicides. HGCA are actively supporting work with LINK funding to investigate the implications of these mutations and methods to reduce selection for such mutations.
The I381V mutation was first found in 2000 and once present is strongly selected for by azole use. Tebuconazole selects strongly for this mutation. An unusual phenomenon is that prochloraz exerts a negative selection for this mutation. When prochloraz is applied to a population of S. tritici the remaining population has a lower frequency of the I381V mutation – potentially making the population more sensitive to any subsequent azoles applied. Work is in progress to investigate the practical application of this effect. | 
