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

Dramatic recent changes in the population genetic diversity of the Zymoseptoria tritici effector gene AvrStb6

Chris Stephens*
Rothamsted Research, Harpenden, UK

Fatih Ölmez
Şirnak University, Şirnak, Turkey

Hannah Blyth
Rothamsted Research, Harpenden, UK

Emine Burcu Turgay
Field Crops Central Research Institute, Ankara, Turkey

Hongxin Chen
Rothamsted Research, Harpenden, UK

Megan McDonald
Australian National University, Canberra, Australia

Peter Solomon
Australian National University, Canberra, Australia

Andrew Milgate
NSW Department of Primary Industries, Wagga Wagga, Australia

Bart Fraaije
Rothamsted Research, Harpenden, UK

Jason Rudd
Rothamsted Research, Harpenden, UK

Kostya Kanyuka
Rothamsted Research, Harpenden, UK

Oral Presentation
Evolution and Population Biology

Moore Auditorium, UCD O'Brien centre for Science
22 May 2019, 11:00

View this abstract online by visting

Zymoseptoria tritici, the causal agent of Septoria tritici blotch (STB), is among the most commercially important global pathogens of wheat. Recently, both genetic factors of the previously characterised gene-for-gene interaction between Z. tritici and wheat have been identified: the wheat receptor-like kinase Stb6 and the Z. tritici secreted protein AvrStb6. Subsequently, historic collections of Z. tritici collected around the world have been used to analyse AvrStb6 genetic diversity. However, which of the identified AvrStb6 haplotypes confer virulence on wheat possessing Stb6 and the frequency of virulence in the global populations remain unknown. Here, we re-sequenced AvrStb6 from recent field populations of Z. tritici collected between 2014 and 2017 from Western Europe, Turkey, USA, South America, and Australia. 

As well as AvrStb6 being present in all isolates tested, we found a small number of haplotypes, all encoding the same protein isoform conditioning virulence on Stb6-containing wheat, predominate in different parts of the world. The avirulence isoform of AvrStb6, first used to characterise the gene-for-gene interaction in this pathosystem, was not detected. This contrasts with findings from a study of global Z. tritici populations sampled between 1990 and 2001 (Brunner & McDonald, 2018) that identified a high AvrStb6 haplotype diversity and no clear dominance of a single haplotype, and a study of a Z. tritici population sampled between 2009-2010 predominantly from France where the avirulence isoform was detected in ~20% of isolates (Zhong et al. 2017). It would appear that a significant shift in the global Z. tritici populations, towards a single Stb6 resistance-breaking isoform of Avrstb6, has taken place in recent years. We hypothesise that selection pressure imposed by Stb6 haplotypes present in many contemporary commercial wheat cultivars may be responsible for this shift. This work will help to pinpoint specific amino-acid changes in AvrStb6 that allow evasion of Stb6 detection.



Brunner P & McDonald B (2018) Molecular Plant Pathology 19: 1836-46; Saintenac C et al. (2018) Nature Genetics 50: 368-74; Zhong Z et al. (2017) New Phytologist 214: 619-31.