| Summary: | Drought is a major factor limiting plant development and negatively affecting crop yield. It was reported that mutants defective in the brassinosteroid (BR) metabolism from several species, including barley (<i>Hordeum vulgare</i>), show improved tolerance to drought during the vegetative phase of growth. Hence, semi-dwarf barley mutants defective in the BR metabolism may be regarded as an alternative in breeding programs. Occurrence of drought during spike development has a profound effect on yield. Thus, determining reaction of the semi-dwarf, BR-deficient barley mutants to drought during the reproductive phase is crucial. This study was conducted on barley Near-Isogenic Lines defective in the BR metabolism and the reference ‘Bowman’ cultivar. The experiments were performed under laboratory (optimal watering and drought) and field conditions. The following yield-related parameters were analyzed: total tillering, productive tillering, average grain weight per plant and per spike, as well as weight of 1000 seeds. Additionally, an analysis of chemical composition of grain was performed. The BR-insensitive BW312 line showed the highest values of the productive tillering and grain weight per plant under the drought conditions. Perturbations in the BR metabolism did not have any significant deteriorating effect on the contents of grain chemical ingredients.
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