Fine mapping quantitative resistances to downy mildew in lettuce revealed multiple sub-QTLs with plant stage dependent effects reducing or even promoting the infection

• Published in: Theoretical and applied genetics 2013-12, Vol.126 (12), p.2995-3007
• Main Authors: den Boer, Erik, Zhang, Ningwen W, Pelgrom, Koen, Visser, Richard G. F, Niks, Rients E, Jeuken, Marieke J. W
• Format: Article
• Language: English
• Subjects: Agriculture; backcross inbred lines; backcrossing; Biochemistry; Biomedical and Life Sciences; Biotechnology; bremia-lactucae; Chromosome Mapping; Chromosomes, Plant - genetics; Cloning; disease resistance; Disease Resistance - genetics; Diseases and pests; DNA, Plant - genetics; downy mildew; durable resistance; Genes; Genes, Plant - genetics; Genetic aspects; genetic dissection; Genetic Markers - genetics; Health aspects; Immunity, Innate - genetics; inbred lines; Infections; introgression; isogenic lines; Lactuca - genetics; Lactuca - growth & development; Lactuca - immunology; Lactuca - microbiology; Lactuca saligna; leaf rust; Lettuce; Life Sciences; loci; Mildew; nonhost resistance; Original Paper; Peronospora - physiology; Physiological aspects; Plant Biochemistry; Plant Breeding/Biotechnology; Plant diseases; Plant Diseases - genetics; Plant Diseases - immunology; Plant Diseases - microbiology; Plant Genetics and Genomics; Plant immunology; Quantitative Trait Loci; stripe rust; trait locus qtl; wild lettuce
• ISSN: 0040-5752; 1432-2242
• DOI: 10.1007/s00122-013-2188-4

KEY MESSAGE : Three regions with quantitative resistance to downy mildew of non-host and wild lettuce species, Lactuca saligna , disintegrate into seventeen sub-QTLs with plant-stage-dependent effects, reducing or even promoting the infection. Previous studies on the genetic dissection of the complete resistance of wild lettuce, Lactuca saligna, to downy mildew revealed 15 introgression regions that conferred plant stage dependent quantitative resistances (QTLs). Three backcross inbred lines (BILs), carrying an individual 30–50 cM long introgression segment from L. saligna in a cultivated lettuce, L. sativa, background, reduced infection by 60–70 % at young plant stage and by 30–50 % at adult plant stage in field situations. We studied these three quantitative resistances in order to narrow down their mapping interval and determine their number of loci, either single or multiple. We performed recombinant screenings and developed near isogenic lines (NILs) with smaller overlapping L. saligna introgressions (substitution mapping). In segregating introgression line populations, recombination was suppressed up to 17-fold compared to the original L. saligna × L. sativa F ₂ population. Recombination suppression depended on the chromosome region and was stronger suppressed at the smallest introgression lengths. Disease evaluation of the NILs revealed that the resistance of all three BILs was not explained by a single locus but by multiple sub-QTLs. The 17 L. saligna-derived sub-QTLs had a smaller and plant stage dependent resistance effect, some segments reducing; others even promoting downy mildew infection. Implications for lettuce breeding are outlined.