Comparative Mapping of β‐Amylase Activity QTLs among Three Barley Crosses

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Abstract
β‐Amylase (BA) is one of the starch‐degrading enzymes active in germinating barley (Hordeum vulgare L.). Unlike α‐amylase (AA), it is not synthesized de novo at the onset of germination, but accumulates during seed development. BA activity is an important malting quality parameter and is a major contributor, along with AA, to diastatic power (DP). The objectives of this study were to (i) measure and map BA activity in three crosses of North American barleys, (ii) compare quantitative trait loci (QTLs) for BA among various crosses, and (iii) determine the relationship between BA and previously mapped DP QTLs. Comparative mapping was done by means of a consensus map with common markers from F1 doubled haploid mapping populations from the crosses of ‘Steptoe’ × ‘Morex’ (S/M), ‘Harrington’ × TR306 (H/T), and Harrington × Morex (H/M). BA activity analyses were performed with field‐grown seed from the three mapping populations and parents. Relatively normal frequency distributions for enzyme activity were obtained from each of the mapping populations. QTLs for BA were identified in all three crosses and on all seven chromosomes. Seven QTLs were located in S/M, the most genetically diverse cross, while only three each were found in H/T and H/M. As expected, BA QTLs were almost always found in conjunction with previously identified DP QTLs. A survey of QTL literature of populations of diverse germplasm showed many QTLs for BA and DP in common with those identified herein and some unique QTLs as well. The results of this study suggest the benefits of identifying markers closely associated with major BA QTLs are to allow for further molecular studies and for marker assisted selection of this trait.