POTENTIAL OF DOUBLED-HAPLOID LINES AND LOCALIZATION OF QUANTITATIVE TRAIT LOCI (QTL) FOR PARTIAL RESISTANCE TO BACTERIAL LEAF STREAK (XANTHOMONAS-CAMPESTRIS PV. HORDEI) IN BARLEY

Genetic variability for partial resistance to bacterial leaf streak in barley, caused by Xanthomonas campestris pv. hordei, was investigated in 119 doubled-haploid lines (DH) developed by the Hordeum bulbosum m ethod from the F-1 progeny of the cross between two cultivars, 'Morex' (resistant) and 'Steptoe' (susceptible). Two experiments were underta ken in a randomized complete block design with three replicates, in a controlled growth chamber. Twenty seeds per replicate were planted in plastic containers (60 x 40 x 8 cm) containing moistened vermiculite. At the two-leaf stage seedlings were inoculated with an Iranian strain of the pathogen. Genetic variability was observed among the 119 DH li nes for partial resistance to the disease. Some DH lines were signific antly more resistant than 'Morex' (resistant parent) to bacterial leaf streak. Genetic gain in percentage of resistant parent for 5% of the selected DH lines was significant (47.70% and 33.72% in the first and the second experiment, respectively). A QTL analysis of bacterial leaf streak resistance showed that three QTLs were detected on chromosomes 3 and 7. Multilocus allelic effects of the three QTLs account for alm ost 54% of the mean difference between the parents and nearly 30% of t he phenotypic variation of the trait in the mean experiment. The resis tance locus on chromosome 3, near ABG377, appears to be a major gene.