Association mapping of quantitative resistance for Leptosphaeria maculans in oilseed rape (Brassica napus L.)

Abstract

Stem canker caused by the fungus Leptosphaeria maculans is a major disease of Brassica napus. Quantitative resistance factors appear to be important components for effective and durable control of this pathogen. Quantitative trait loci (QTL) for stem canker resistance have previously been identified in the Darmor variety. However, before these QTL can be used in marker-assisted selection (MAS) to breed resistant varieties, they must be validated in a wide range of genetic backgrounds. We used an association mapping approach to confirm the markers located within the QTL previously identified in Darmor and establish their usefulness in MAS. For this, we characterized the molecular diversity of an oilseed rape collection of 128 lines showing a large spectrum of responses to infection by L. maculans, using 72 pairs of primers for simple sequence repeat and other markers. We used different association mapping models which either do or do not take into account the population structure and/or family relatedness. In all, 61 marker alleles were found to be associated with resistance to stem canker. Some of these markers were associated with previously identified QTL, which confirms their usefulness in MAS. Markers located in regions not harbouring previously identified QTL were also associated with resistance, suggesting that new QTL or allelic variants are present in the collection. All of these markers associated with stem canker resistance will help identify accessions carrying desirable alleles and facilitate QTL introgression

Molecular mapping of qualitative and quantitative loci for resistance to Leptosphaeria maculans causing blackleg disease in canola (Brassica napus L.)

“…However, it was difficult to compare loci conferring blackleg resistance due to the different marker systems used in the mapping studies (Kaur et al 2009;Yu et al 2005). Several other QTLs that we identified in this study correspond to genomic regions associated (based upon their linkage with a common set of markers) with blackleg resistance that have been identified using both classical QTL and association mapping approaches (Delourme et al 2008;Jestin et al 2011;Piquemal et al 2005). The conservation of QTLs between Australian and French studies is interesting and suggests the non-specificity of these QTLs, irrespective of the environment, genetic background, and G 9 E interactions.…”

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

“…The material was chosen among a set of varieties described in Jestin et al (2011). To increase the likelihood of identifying a diverse range of QTL, the varieties were genetically divergent from the variety 'Darmor' used in the previous studies and as divergent as possible from each other.…”

“…Another study was also published on the search for QTL in four biparental mapping populations between 'Westar' (susceptible) and three resistant varieties 'Caiman' (CmW), 'Canberra' (CbW) and 'Sapphire' (SW) and between two resistant lines 'Rainbow' 9 'Sapphire' (RW) in Australia (Kaur et al 2009). Jestin et al (2011) andFopa Fomeju et al (2014) used an alternative approach based on association mapping on an oilseed rape collection.…”

Research fields, challenges and opportunities in European oilseed crops breeding

“…Despite of the strong differences in the life style of the two pathogens, the interactions between them and the crops present some similarities. Indeed, in each case, both qualitative, genotype specific interactions -and their overcoming by new virulent pathotypes -and quantitative, non genotype specific interactions were found (Brun et al, 2010, Jestin et al, 2011, Tourvielle et al, 2008, Vear et al, 2008. Consequently, the scenarios to make the best use of the available genetic diversity together with participatory practices (Hossard et al, 2013, Tourvieille et al, 2005 might present some convergences.…”