Connected populations for detecting quantitative resistance factors to phoma stem canker in oilseed rape [i](Brassica napus[/i] L.)

International audience; Improvement of effectiveness and durability of disease resistance in crops most often relies on the use of quantitative resistance, with the hypothesis that a wide range of quantitative resistance factors (QTL) makes the overcoming of the resistance by the pathogen more difficult. For an optimum use of these QTL in effective and durable strategies of resistance deployment, there is a need to precisely know their localization but also their stability/specificity and their allelic effects in various genetic backgrounds. Stem canker caused by the fungus Leptosphaeria maculans is one of the most important diseases in oilseed rape. In this Brassica napus-L. maculans pathosystem, QTL were previously identified by linkage analysis using populations derived from biparental crosses that were analyzed separately. In this study, we explored new quantitative resistance factors using a multi-cross connected design derived from four resistant lines crossed with a single susceptible line. Independent and connected mapping analyses revealed to be complementary to get an overview of QTL organization. We validated different QTL across different years and genetic backgrounds and identified novel QTL which had not yet been mapped. Population-common and population-specific QTL were identified. Knowledge of QTL organization and effects should help in the rational choice of relevant factors in breeding resistant genotypes to be integrated with other control means such as cultural practices and rotations for durable management of the disease