A new mutation in UK septoria populations, that could have implications for SDHI fungicide efficacy, has been detected at a field site in the south of England.
The septoria isolates, which carry the same mutation as detected in Ireland in 2015, were discovered as part of an AHDB Cereals & Oilseeds monitoring project led by Rothamsted Research.
In 2015, wheat leaf samples were collected from 12 sites across the UK.
From the samples, 1,168 septoria isolates were isolated and tested for fungicide sensitivity in the laboratory.
One site in southern England yielded 144 isolates and two of these were classified as having medium to high resistance to SDHI fungicides.
Subsequently, the two isolates were confirmed as having the Sdh C-H152R mutation, which affects SDHI target site genes.
The mutation makes septoria isolates significantly less sensitive to SDHI chemistry. It the first instance of its occurrence in a UK isolate.
Sdh C-H152R was first identified in samples taken in Ireland by Teagasc in 2015.
Laboratory tests, reported by Teagasc, found that isolates with the Sdh C-H152R mutation survived up to 100 times the concentration of SDHI fungicides compared to the most insensitive isolates found in previous years.
Lead researcher on the project, Bart Fraaije of Rothamsted Research, said: “As these isolates display a higher resistance factor, it has a greater potential to spread in field populations under SDHI fungicide selection pressure than previously reported mutations.
“In the coming season, we will be using rapid molecular tools to monitor septoria isolates in the field to determine if the new mutant isolate is spreading.”
AHDB research manager Paul Gosling, who is responsible for work on fungicides, said: “The full implications of this discovery are as yet unknown. The frequency of the isolate was low at this site and so field performance in 2016 is unlikely to be impacted.
“Additionally, some mutations carry a significant fitness penalty for the pathogen, meaning that it spreads only slowly or not at all.
“However, it is a timely warning for growers ahead of the 2016 spraying season that the threat from fungicide resistance must be taken seriously and all appropriate resistance management strategies must be deployed in the field.”
Following several reports of laboratory and field isolates of septoria tritici with reduced sensitivities to SDHI fungicides, AHDB published a statement by FRAG-UK in December 2015.
The statement provides a timeline of discovery and the latest resistance management guidance.
The new UK Sdh C-H152R mutation was detected as part of a long-term project which aims to identify changes to the CYP51 gene (targeted by triazole fungicides) and mutations in the Sdh gene (targeted by the SDHI group of fungicides) in field populations of septoria (Zymoseptoria tritici).
As part of the project, any changes in sensitivity of septoria measured in the lab are linked to specific changes in the target gene.
Latest data from AHDB Cereals & Oilseeds fungicide performance trials show that SDHIs are the most active chemistry against septoria when applied in protectant situations.
However, in accordance with FRAG-UK guidance, growers are advised to limit the number of applications to two SDHI fungicide containing sprays and always use SDHI fungicides in mixture with at least one fungicide from an alternative mode of action group which has comparable efficacy against the target pathogen(s).