AUTOTETRAPLOIDS AND GENETIC-MAPPING USING COMMON AFLP MARKERS - THE R2 ALLELE CONFERRING RESISTANCE TO PHYTOPHTHORA-INFESTANS MAPPED ON POTATO CHROMOSOME-4

Due to the complexity of tetrasomic inheritance, mapping studies in po tato (Solanum tuberosum L.) are generally conducted at the diploid lev el. In the present study we tested the feasibility of Bulked Segregant Analysis (BSA) using a tetraploid offspring for the identification of AFLP markers linked to the R2 allele, which confers race-specific res istance to Phytophthora infestans. Eleven bulk-specific AFLP markers, detected in fingerprints of 205 AFLP primer combinations, could be map ped in a linkage group encompassing the R2 locus. The efficiency of BS A at the tetraploid level, determined by the frequency of single-dose restriction fragments (SDRF), was much higher than expected on the bas is of overall genetic dissimilarity between the parental clones. The f ortuitous detection of AFLPs with linkage to the R2 allele is explaine d on the basis of specific genetic dissimilarity between cultivated po tato and the chromosomal segment introgressed from S. demissum carryin g the resistant R2 allele. AFLP markers common to those with linkage t o R2 were visually recognized by their electrophoretic mobility in the AFLP fingerprint in a parental done of a reference mapping population . Using these common AFLP markers we anchored the linkage group compri sing the R2 allele to potato chromosome 4.