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

Abstract

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.

Genetic control of compatibility in crosses between wheat and its wild or cultivated relatives

“…Linkage drag arises as an effect of recombination suppression at the introgressed locus (Wulff and Moscou, 2014 ; Figure 4 ). Such reduction in recombination was described for tomato (Brouwer and St Clair, 2004 ; Paterson et al ., 1990 ), barley (Johnston et al ., 2013 ) and lettuce (Den Boer et al ., 2013 ) especially when the introgressed parent species is distantly related to the recurrent parent. Moreover, suppression of recombination becomes stronger as the size of the introgressed segments becomes smaller (Brouwer and St Clair, 2004 ; Canady et al ., 2006 ; Johnston et al ., 2013 ).…”

Innovative breeding technologies in lettuce for improved post-harvest quality

“…“Olof” F 2 population Jeuken and Lindhout, 2002 QTL for downy mildew resistance and QTL fine-mapping reported Backcross inbred lines (BC 4 ) developed by crossing lines of an L. saligna (CGN 5271) x L. sativa cv. “Olof” F 2 population to the L. sativa parent Jeuken et al, 2008 ; Zhang et al, 2009a , 2009b den Boer et al, 2013 QTL for downy mildew resistance L. sativa cvs. “Iceberg” x “Grand Rapids” RIL population Simko et al, 2013 QTL for downy mildew resistance L. sativa cv.…”