QTLs in barley controlling seedling elongation of deep-sown seeds

In drought areas, in which topsoil moisture is low, barley seeds are generally sown in the subsoil (deep-seeding). In order for the shoots of germinating seeds to emerge from the deep soil cover, the coleoptile and the first internode of the seedlings must elongate as an adaptive response to deep-seeding. Here, we have mapped quantitative trait loci (QTLs) for these adaptive characteristics. Elongation of the coleoptile and first internode was investigated using seeds sown under two soil cover conditions: at a depth of 9 cm beneath a soil mixture; and, at a depth of 12 cm beneath vermiculite. We identified multiple alleles for increased coleoptile and first internode elongation using a doubled haploid population of 150 lines generated from a cross between the barley cultivars Harrington and TR306. Composite interval mapping analyses of the data revealed two moderate and eleven small effect QTLs, with at least one QTL on each chromosome. The QTLs on chromosomes 5H and 7H had moderate effects on coleoptile elongation (18.5-27.6% of PVE: phenotypic variance explained; 2.6-3.2 mm of Add: additive effect) and first internode elongation (PVE: 16.6-19.6%; Add: 3.1-3.2 mm). The small effect QTLs showed PVEs of less than 15% and an Add range of 1.2-3.2 mm for both characters. A marker assisted selection approach, using markers linked to the QTLs for seedling elongation at deep-seeding, may eventually enable development of drought tolerant barley hybrids.