Individual locus effects on dormancy during seed development and after ripening in barley

Genetic control of seed dormancy in barley (Hordeum vulgare L.) has been st udied recently by means of quantitative trait loci (QTL) mapping. Four QTL, designated SD1 to SD4, were found associated with about 75% of the phenoty pic variation for dormancy in 'Steptoe'/ 'Morex' crosses, The objective of this study was to investigate the individual effects of seed dormancy (SD) QTL and the nature of their epistatic interactions on dormancy during seed development and after ripening. Six F-1-derived doubled haploid lines from Steptoe-Morex crosses, selected on the basis of the flanking marker alleles for the four SD QTL, and the two parents were grown under greenhouse condi tions. The same lines and four additional doubled haploid lines from the sa me cross were also grown in a field experiment. Genotypic dependence of ons et, maintenance, and release of dormancy was studied, To assess dormancy, g ermination tests of excised embryos from fresh and artificially dried seed were conducted during seed development. All genotypes showed a similar patt ern of germination of excised embryos, Since no differences in the time of dormancy inception were found, this phenomenon does not seem to be controll ed by the SD QTL, Rather, the SD QTL were involved in the release of dorman cy at the end of the development process and during after ripening, The pre sence of the Steptoe allele at SD1 on chromosome 7 (5H) kept precocious ger mination to a minimum until the end of the seed development process, On the basis of the dormancy profiles at after ripening, genotypes could be class ified as affecting early, intermediate, and late dormancy release. These gr oups Here genotypically dependent. A model for allele interactions among th e SD QTL was developed.