Supplementary files from the PhD thesis "The cryptic inheritance of genetic resistance of potato against common scab"

Common scab (CS), caused by Streptomyces species, is a major skin blemish disease in potatoes worldwide, leading to 30-50% crop loss in severely affected fields. The disease causes raised, superficial or pitted lesions on potato tubers. Resistant varieties are the most effective scab management, as irrigation-based control is costly and unsustainable long-term. However, phenotypic testing for CS resistance is difficult and frequently unreliable. My project aims to develop genotypic and phenotypic tools to enhance selection of resistant varieties. This will improve breeding efficiency and reduce costs compared to conventional field screening methods. To enable genome-based selection for CS resistance, I aim to identify genomic regions associated with resistance in different potato backgrounds, old and modern tetraploid and diploid varieties. To achieve this, I have performed genome-wide association studies (GWAS) in a range of potato varieties and breeding material: one on historical and US phenotypic data for scab resistance, another on two tetraploid bi-parental populations, and one on a dihaploid (diploid derived from a tetraploid) population. Briefly, these have demonstrated that CS resistance is under the control of multiple small-effect regions in potato, making it likely that genomic selection is the most appropriate approach to improve selection. A rapid phenotypic test for CS resistance would contribute an increased capacity for selection in breeding and advance our understanding of the mechanism of resistance to scab. To facilitate these goals, I developed a rapid in-vitro method to screen for resistant plants and test differential interactions between potato varieties and scab-causing species.