In most production areas, Alternaria leaf blight (ALB) is recognized as the most common and destructive foliage disease in carrot. To assess the genetic architecture of carrot ALB resistance, two parental coupling maps were developed with similar number of dominant markers (around 70), sizes (around 650 cM), densities (around 9.5 cM), and marker composition. The F(2:3) progenies were evaluated in field and tunnel for two scoring dates. The continuous distribution of the disease severity value indicated that ALB resistance is under polygenic control. Three QTLs regions were found on three linkage groups. Two of them were tunnel or field specific and were detected only at the second screening date suggesting that the expression of these two QTLs regions involved in resistance to Alternaria dauci might depend on environment and delay after infection.