Drought Stress Response of Doubled Haploid Interspecific Rapeseed Hybrids at Germination and Flowering Stages

Drought stress is a major limiting factor for canola production in arid and semi-arid regions, particularly during seed germination, seedling and flowering stages. In this study, we evaluated drought responses of doubled haploid (DH) lines derived from interspecific hybrids of <i>B. napus</i> × <i>B. rapa</i> and their parental cultivars under simulated (PEG-6000) and soil-based drought conditions. Drought stress significantly reduced germination, growth, and physiological performance in all genotypes; however, DH lines consistently exhibited superior tolerance. Under PEG-induced osmotic stress, DH lines maintained higher germination rates, root elongation, and relative water content compared with parental genotypes. During seedling and flowering stages drought, DH lines showed lower accumulation of hydrogen peroxide and malondialdehyde, alongside markedly higher antioxidant enzyme activities (CAT and POD) and improved photosynthetic efficiency (Fv/Fm). Gene expression analysis revealed strong induction of drought-responsive genes, including <i>WRKY28</i>, <i>MYB</i>, <i>LTP</i>, <i>WSP</i>, <i>metallothionein</i>, and protein kinase family genes, particularly in DH lines at prolonged stress exposure. Multivariate analyses (PCA and correlation) confirmed a close association between enhanced antioxidant capacity, transcriptional activation, and drought tolerance traits. Overall, our results demonstrate that homozygous doubled haploid lines derived from distant hybridization between <i>B. napus</i> and <i>B. rapa</i> exhibit enhanced drought tolerance at both early and reproductive stages. These genotypes represent valuable genetic resources for breeding drought-tolerance canola cultivars.