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

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Dutta, Anik
Croll, Daniel
McDonald, Bruce A.
Krattinger, Simon G.

KAUST Department
Biological and Environmental Science and Engineering (BESE) Division
Plant Science

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Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is a major constraint in global wheat production. The lack of genetic diversity in modern elite wheat cultivars largely hinders the improvement of STB resistance. Wheat landraces are reservoirs of untapped genetic diversity, which can be exploited to find novel STB resistance genes or alleles. Here, we characterized 188 Swiss wheat landraces for resistance to STB using four Swiss Z. tritici isolates. We used a genome-wide association study (GWAS) to identify genetic variants associated with the amount of lesion and pycnidia production by the fungus. The majority of the landraces were highly resistant for both traits to the isolate 1E4, indicating a gene-for-gene relationship, while higher phenotypic variability was observed against other isolates. GWAS detected a significant SNP on chromosome 3A that was associated with both traits in the isolate 1E4. The resistance response against 1E4 was likely controlled by the Stb6 gene. Sanger sequencing revealed that the majority of these ~ 100-year-old landraces carry the Stb6 resistance allele. This indicates the importance of this gene in Switzerland during the early 1900s for disease control in the field. Our study demonstrates the importance of characterizing historic landrace collections for STB resistance to provide valuable information on resistance variability and contributing alleles. This will help breeders in the future to make decisions on integrating such germplasms in STB resistance breeding.

Dutta, A., Croll, D., McDonald, B. A., & Krattinger, S. G. (2021). Genome-wide association study for septoria tritici blotch resistance reveals the occurrence and distribution of Stb6 in a historic Swiss landrace collection. Euphytica, 217(6). doi:10.1007/s10681-021-02843-7

This work was funded by the Swiss Federal Office for Agriculture (BLW) in the framework of NAP-PGREL (National Plan of Action for the Conservation and Sustainable Utilization of Plant Genetic Resources) Project Nr. 627000640. We are thankful to Dr. Fabio Mascher, Dr. Dario Fossati, and Beate Schierscher for providing valuable discussions on the history of these landraces in STB resistance breeding. We thank Dr. Danilo Dos Santos Pereira, Alessio Bernasconi, Dr. Petteri Karisto, Maria Zwyssig and Susanne Dora for help in collecting phenotypic data.

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