Electronic supplementary material (ESM S1-S5) for a study that redeveloped a KASP marker for the H1 potato cyst nematode (PCN) resistance locus in potato. Bulked resequencing data from Meade et al. (2020) were re-analysed with the CoSSA k-mer subtraction approach. H1-associated k-mers were extracted and mapped to the DM potato reference genome, giving 99 candidate SNPs near the diagnostic 57R marker region. Two SNPs were converted to KASP assays and tested on three years of breeding material. One gave a modest but statistically significant improvement in classification accuracy over the previously published marker. The dataset documents a low-cost workflow for turning reference-free k-mer signals from public sequence data into breeder-ready marker assays. It contains: the k-mer datasets and set operations used (S1); the effect of k-mer depth thresholds on genome-wide signal and H1 enrichment (S2, S3); multi-year KASP calls with phenotypic PCN resistance data for the validation panel (S4); and the 99 candidate SNPs (S5).
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