Generation and Screening of a BAC Library from a Diploid Potato Clone to Unravel Durable Late Blight Resistance on Linkage Group IV

We describe the construction and screening of a large insert genomic library from the diploid potato clone HB171(13) that has been shown to express durable quantitative field resistance to Phytophthora infestans, the causal agent of potato late blight disease. Integrated genetic mapping of the field resistance quantitative trait locus with markers developed from populations segregating for Rpi-blb3, Rpi-abpt, R2, and R2-like resistance, all located on linkage group IV, has positioned the field resistance QTL within the proximity of this R gene cluster. The library has been successfully screened with resistance gene analogues (RGA) potentially linked to the R gene cluster. Over 30 positive BAC clones were identified and confirmed by PCR and Southern hybridisations to harbour RGA-like sequences. In addition, BAC end sequencing of positive clones has corroborated two BAC clones with a very high level of nucleotide similarity to the RGA probes utilised.