International Symposium on Cereal Leaf Blights 2019 | University College Dublin, Ireland | 22-24 May 2019

Investigation of Isolates of Zymoseptoria tritici able to overcome the resistance in the winter wheat cultivar Cougar

Eda Naska

Rosa Caiazzo
Agriculture and Agri-Food Canada Swift Current Research and Development Centre

Anne Webb

Bart Fraaije
Rothamsted Research

Serena Di Lenarda

Denise Elliott

Sarah Wilderspin

Jacqueline Sammonds

James Brown
John Innes Centre

Jane Thomas

Thomas Wood

Sarah Holdgate*

Poster Presentation
Host-Pathogen Interactions

Atrium, UCD O'Brien centre for Science
Poster 31

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Resistance in winter wheat to Septoria leaf blotch, caused by Zymoseptoria tritici (Zt), can be governed by the gene-for-gene interaction.  Thus new races of Zt could appear and render some forms of cultivar resistance ineffective, as is the case for the cereal rusts and mildews.  In practice under field conditions, it is rare to see a change in race that causes a variety to become more susceptible.  In 2015 in the UK, the variety Cougar, rated as the most resistant cultivar in use at the time, became markedly more susceptible to Septoria leaf blotch in different locations across the country.  To investigate this further, sentinel plots were established in the following season at breeding sites across the UK.  Samples of Septoria leaf blotch were taken and from each sample, three isolates of Zymoseptoria tritici were collected.  These were tested on seedlings of the cultivars Cougar and Gallant, the latter being a susceptible control, to classify isolates as being “Cougar”-type or “non-Cougar”-type.  Five isolates of each were then tested further to assess their risk to other resistant varieties in the UK at both the seedling and adult plant stages.  Alongside these tests, fungicide resistance assays were conducted and genotyping of isolates with a set of 21 microsatellite markers1 was performed. Genotyping data from the 2016 isolates demonstrated high levels of genetic diversity as expected for a sexually-reproducing organism, and it was not possible distinguish between Cougar and non-Cougar types based on genotypes alone. These experiments were repeated in 2017 and results will be presented to show the potential impact of such changes in pathogenicity along with hypotheses on the evolution of the Cougar- infecting isolates.

Gautier et al., Development of a rapid multiplex SSR genotyping method to study populations of the fungal plant pathogen Zymoseptoria tritici. BMC Research notes 7:373