Remarkable recent changes in the genetic diversity of the avirulence gene AvrStb6 in global populations of the wheat pathogen Zymoseptoria tritici

Abstract

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Detection of virulence to septoria tritici blotch (STB) resistance conferred by the winter wheat cultivar Cougar in the Irish Zymoseptoria tritici population and potential implications for STB control

“…tritici genome. Brunner and McDonald (2018) and Stephens et al (2021) have demonstrated how the profile of Avrstb6 in global Z . tritici populations has evolved to overcome Stb6 , with the original avirulent isoform all but absent in modern populations.…”

“…As the Cougar avirulent isolate S19.2.1 was able to infect Cadenza and cause high levels of STB, it can be assumed that the virulence towards Cougar is not just a case of virulence to Stb6. AsStephens et al (2021) have reported that the recent global Z. trit-…”

“…As the Cougar avirulent isolate S19.2.1 was able to infect Cadenza and cause high levels of STB, it can be assumed that the virulence towards Cougar is not just a case of virulence to Stb6. AsStephens et al (2021) have reported that the recent global Z. tritici populations, including Irish populations, are almost exclusively dominated by Stb6 virulent isolates, it was highly unlikely that this was the case. In this context it is surprising that the other Cougar avirulent isolates tested, S19.3.1 and S19.4.1, were both avirulent on Cadenza.…”

“…Zhong et al (2017) identified this effector (Avrstb6) as a small cysteine-rich protein whose corresponding gene is located in a highly adaptable region of the Z. tritici genome. Brunner and McDonald (2018) and Stephens et al (2021) have demonstrated how the profile of Avrstb6 in global Z. tritici populations has evolved to overcome Stb6, with the original avirulent isoform all but absent in modern populations. In total, 22 qualitative STB resistance genes have been identified (Brown et al, 2015), with two of these, Stb6 (as detailed above) and Stb16q, now characterized (Saintenac et al, 2018(Saintenac et al, , 2021.…”

Genome-wide association study for septoria tritici blotch resistance reveals the occurrence and distribution of Stb6 in a historic Swiss landrace collection

“…Stb6 encodes a wall-associated receptor kinase (WAK) and follows a gene-for-gene relationship with the corresponding avirulence gene AvrStb6 (Zhong et al 2017). A recent study (Stephens et al 2020) found that resistance conferred by Stb6 in wheat cultivars around the world has been overcome by widespread occurrences of AvrStb6 virulence alleles in fungal populations.…”