A QTL-study on quantitative maturity-corrected resistance to late blight (Phytophthora infestans) in tetraploid ootato (Solanum tuberosum)

Late blight (Phytophthora infestans) is the most serious disease in potato production worldwide and causes tremendous losses in yield and high costs in plant protection. In order to facilitate breeding for quantitative resistance against late blight, a QTLstudy was initiated. A full-sib population of 302 tetraploid clones derived from a cross between the tetraploid clone GL-93.7015.04 and the commercial variety ‘Delikat’ was phenotyped and genotyped. Phenotyping was done as scoring of percent leaf area infested by P. infestans in a field trial untreated with fungicides over a period of three years with two replications at one location in each year. In parallel an experiment treated with fungicides was run to collect maturity data for each clone. To eliminate the influence of maturity a maturity-corrected resistance parameter was calculated and used as phenotypic trait in the QTL-study. Genotyping was done by AFLP markers. A single-allele test was performed using the Kruskal-Wallis test. Four AFLP markers tagging three locations in the genome were found to be associated with maturity-corrected resistance to late blight.