Comparative mapping of a QTL controlling black point formation in barley

The dark discoloration of the embryo end of barley grain (known as black point) is a physiological disorder and the discovery of a quantitative trait locus (QTL) on 2H confirms this trait is controlled genetically. The mechanisms underlying black point tolerance can now be dissected through identification of candidate genes. Comparisons between the QTL identified on chromosomes 2H of barley and 2B of wheat suggest that they are in similar positions near the centromere. In silico analysis, using rice, identified genes residing on two comparative chromosomes (4 and 7) of the rice genome. Analysis of the 12.6 Mb region revealed 1928 unique annotations classified into 11 functional categories. Expressed sequence tags (ESTs) with high sequence similarity to enzymes proposed to be involved in black point formation were used to develop restriction fragment length polymorphisms (RFLPs). To ensure an even coverage of markers across the QTL, RFLP markers were also developed from other ESTs. Mapping of these markers has reduced the QTL region from 28 to 18 cM. This study has identified candidate genes for the control of black point formation and paves the way for future research to develop black point resistant barley cultivars.