GENETIC-MAPPING OF A QUANTITATIVE TRAIT LOCUS (QTL) THAT ENHANCES THE SHOOT DIFFERENTIATION RATE IN HORDEUM-VULGARE L

A quantitative trait locus (QTL) controlling shoot differentiation from immature embryo callus was identified by linkage analysis with morphological and isozyme markers in barley, Hordeum vulgare L. Immature embryos were isolated from cvs 'Azumamugi' (difficult to differentiate), 'Kanto Nakate Gold' (easy to differentiate), their hybrids (F1) and a backcross population derived from a cross 'Azumamugi' x F1. The embryos were cultured in vitro for callus initiation and subsequent shoot differentiation. The shoot differentiation rate was closely associated with ear type (v locus), isocitrate dehydrogenase isozyme (Idh-2), and esterase isozyme (Est-11). These markers were found to reside in a chromosome segment of approximately 30 cM on chromosome 2. Recombination frequency was 9.9% between v and a proposed QTL named ''Shd1'' (shoot differentiation), 11.5% between Idh-2 and Shd 1, and 21.3% between Est-11 and Shd1. All data showed the Idh-2, v, Shd1 and Est-11 loci to be arranged in this order from proximal to distal on the long arm of chromosome 2.