QTL and candidate gene mapping for aroma compounds in the apple progeny 'Discovery' x 'Prima'

Flavour is among the key factors of apple fruit quality but in spite of the analytical and biochemical knowledge about volatiles little is known about the genetic and molecular bases of apple aroma. Two parental molecular linkage maps constructed for the apple cultivars ‘Discovery’ and ‘Prima’ were used to identify QTLs for volatile compounds putatively involved in apple aroma. ‘Discovery’ and ‘Prima’ showed very different volatile patterns, and ‘Discovery’ mostly had the higher volatile concentrations in comparison with the Vf- scab resistant ‘Prima’ which has its origin in the small-fruited apple species M. floribunda. About 50 putative QTLs for a total of 27 different apple fruit volatiles were detected through an interval mapping approach by using genotypic data of 150 F1 individuals of the mapping population ‘C3’ together with phenotypic data obtained by HS-SPME (head-space solid phase micro-extraction) gas chromatography. QTLs for volatile compounds putatively involved in apple aroma were found on 12 out of the 17 apple chromosomes. QTLs were mainly clustered on linkage groups LG 2, 3 and 9. In a candidate gene mapping approach, an alcohol acyltransferase gene (MdAAT2) putatively involved in aroma-related volatile metabolism, was mapped on linkage group LG 2. MdAAT2 was found to be associated with a QTL cluster containing QTLs for some important acetate esters such as butyl acetate, hexyl acetate, and 2- methyl butyl acetate.