show Abstracthide AbstractMagnesium (Mg) and calcium (Ca) are essential micronutrients lacking in many human food systems. In grazing livestock, hypomagnesaemia and hypocalcaemia are costly welfare issues. In this study, we idetified an overaccumulator of magnesium and calcium using a forward ionomic screen of chemically mutagenised lines. By backcrossing and 10x Genomics short-read linked-read sequencing of BC2F2 segregants we mapped a single recessive locus and identfied the location and identity of the single base change. This novel breeding target could be used in horticultural and forage Brassica crop improvement programmes, to reduce Mg and Ca deficiencies, in both human and livestock food systems.