GENETIC COMPLEXITY OF THE MALT EXTRACT TRAIT IN BARLEY SUGGESTED BY QTL ANALYSIS

Many economically important traits of crop species are complexly inher ited quantitative traits (QT). Trait expression tends to be continuous due to control by multiple genes (G), the environment (E), and G x G and G x E interactions. The development of comprehensive genome maps a nd quantitative trait locus (QTL) analysis procedures allowed the firs t 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 stud y was to elucidate the genetic characteristics of malt extract primari ly from QTL analyses of the Steptoe x Morex cross. QTL analysis of dat a from the Steptoe x Morex F-1-derived double haploid mapping populati on has revealed the location of five malt extract QTLs on three of bar ley's seven chromosomes. Most of the chromosome regions involved also contain QTLs for other related malting quality traits including alpha- amylase activity, diastatic power, barley and malt beta-glucan content , beta-glucanase activity, and/or seed dormancy. The overlapping QTLs indicate either linked genes or pleitropy or both. Analyses also indic ated additive and G x E interactions for malt extract. Fine mapping of a critical region of chromosome 1 is in progress to elucidate the ove rlapping QTL situation among malt extract and the other quality traits listed above. Location of specific genes for malt extract will facili tate more precise breeding for the improvement of this important trait in barley through molecular marker assisted selection.