Genetic Complexity of the Malt Extract Trait in Barley Suggested by QTL Analysis

Abstract

Many economically important traits of crop species are complexly inherited quantitative traits (QT). Trait expression tends to be continuous due to control by multiple genes (G), the environment (E), and G × G and G × E interactions. The development of comprehensive genome maps and quantitative trait locus (QTL) analysis procedures allowed the first significant examination of the genetic control of QTs. Malt extract is a good example of a QT in barley. Heretofore, little has been known about the genetic control of malt extract. The objective of this study was to elucidate the genetic characteristics of malt extract primarily from QTL analyses of the Steptoe x Morex cross. QTL analysis of data from the Steptoe x Morex F1-derived double haploid mapping population has revealed the location of five malt extract QTLs on three of barley's seven chromosomes. Most of the chromosome regions involved also contain QTLs for other related malting quality traits including α-amylase activity, diastatic power, barley and malt β-glucan content, β-glucanase activity, and/or seed dormancy. The overlapping QTLs indicate either linked genes or pleitropy or both. Analyses also indicated additive and G × E interactions for malt extract. Fine mapping of a critical region of chromosome 1 is in progress to elucidate the overlapping QTL situation among malt extract and the other quality traits listed above. Location of specific genes for malt extract will facilitate more precise breeding for the improvement of this important trait in barley through molecular marker assisted selection.