Mapping of the locus associated with tolerance to high manganese in rapeseed (Brassica napus L.).

Rapeseed germplasm tolerant to high levels of manganese (Mn 2+ ) is becoming increasingly important in areas where oilseed rape is grown on acidic soils. Although rapeseed germplasm tolerant to high Mn 2+ is available currently there are no molecular marker(s) associated with tolerance to high Mn 2+ which may facilitate the introgression of this trait into sensitive material. This study was conducted to develop a molecular marker associated with tolerance to high Mn 2+ . We phenotyped 200 individuals from an F2 population derived from doubled haploid (DH) parental genotypes Mutu-2 (98-6) (Mn-tolerant) and RSO94-67 (Mn-Sensitive) using a full nutrient solution culture with a Mn 2+ concentration of 125 μM. Genetic variation for tolerance to high Mn 2+ in this intercross population was determined on 8-11 day old seedlings by visual and digital analysis of the percentage of chlorosis occurring on the margins of the cotyledons. The visual scores and digital image analysis were strongly positively correlated. The scoring of the F2 population showed a 3:1 tolerant to sensitive segregating ratio which confirmed that tolerance to high Mn 2+ may be controlled by a single locus. We have genotyped a subset of this population comprising 92 individuals, using Diversity Array Technology (DArTTM) markers and mapped a major locus associated with tolerance to high Mn 2+ in the Mutu-2 (98-6)/RSO94-67 population. A suite of DArT markers were identified that map approximately 13.7 centimorgans from the Mn 2+ tolerance locus. We are further saturating and validating this locus with molecular markers, enabling marker assisted selection for breeding rapeseed cultivars for tolerance to high Mn 2+ .