Project description. Six BAC clones overlapping the Rysto region were sequenced

Key message Based on fine-scale genetic mapping, BAC library construction, chromosome walking and DNA sequence analysis six full-length NBS-LRR-type potato genes tightly linked to Rysto were identified and new Rysto markers generated.Virus resistance genes carried by wild species are valuable sources of plant breeding. The Rysto gene conferring a broad spectrum of durable resistance is originated from Solanum stoloniferum and was introgressed into several commercial potato cultivars, including 'White Lady', by classical breeding. To date, Rysto was mapped to chromosome XII in potato and markers used for marker assisted selection in breeding programs were identified. Nevertheless, there is no information on the identity of Rysto gene. To get closer to the identification of Rysto a fine-scale genetic mapping was performed that in combination with chromosome walking narrowed down the locus of the gene to 1 Mb. DNA sequence analysis of the locus identified six full-length NBS-LRR-type (shortly NLR-type) putative resistance genes. Two of them, designated TMV2 and TMV3, were similar to a TMV resistance gene isolated from tobacco and also to Y-1, which co-segregates with Ryadg, the extreme virus resistance gene originated from Solanum andigena and localised to chromosome XI. Functional analysis of the NLR genes was attempted by expressing the genes from their own putative promoters in the virus sensitive cultivar 'Désirée'. Besides, TMV2 and TMV3 were expressed in the virus sensitive breeding line 'S440'. However, as in case of Y-1 earlier, no virus resistant transgenic lines were obtained.