Identification of late blight resistance quantitative trait loci in Solanum pimpinellifolium accession PI 270441

Late blight (LB), caused by the oomycete Phytophthora infestans, is one of the most destructive diseases of the cultivated tomato (Solanum lycopersicum L.) and potato (Solanum tuberosum L.) worldwide. Genetic changes in the pathogen have resulted in the emergence of new genotypes, overcoming formerly effective fungicides or host resistance genes. We previously reported the identification of a LB-resistant accession (PI 270441) of the wild tomato species S. pimpinellifolium L. and the high heritability of its resistance. In the present study, an F₂ population (n = 1,209), derived from a cross between PI 270441 and a LB-susceptible tomato breeding line (Fla. 8059), was screened for response to LB infection. Extreme resistant (n = 44) and susceptible (n = 39) F₂ individuals were selected and used in a trait-based marker analysis (TBA; a.k.a selective genotyping) to identify and map quantitative trait loci (QTLs) conferring LB resistance. Reduced representation libraries (RRLs) of Fla. 8059 and PI 270441 were constructed, sequenced, and mapped to the tomato genome. A total of 13,054 single-nucleotide polymorphisms (SNPs) were identified, of which, 200 were used to construct a genetic linkage map and locate QTLs. Four LB resistance QTLs were identified on chromosomes 1, 10, and 11 of PI 270441. The markers associated with these QTLs can be used to transfer LB resistance from PI 270441 into new tomato cultivars and to develop near-isogenic lines for fine mapping of the QTL.