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

## TL;DR

This study shows that doubled haploid rapeseed hybrids are more drought-tolerant than their parents, making them useful for breeding crops in dry regions.

## Contribution

DH lines from interspecific hybrids show enhanced drought tolerance through superior physiological and gene expression responses.

## Key findings

- DH lines maintained higher germination rates and water content under drought stress compared to parental lines.
- DH lines exhibited lower hydrogen peroxide and malondialdehyde levels and higher antioxidant enzyme activity.
- Drought-responsive genes like WRKY28, MYB, and LTP were strongly induced in DH lines under prolonged stress.

## Abstract

This study evaluated the drought tolerance of doubled haploid (DH) lines derived from interspecific hybrids between rapeseed (Brassica napus) and turnip rape (Brassica rapa), comparing them to their parental lines. Under drought conditions simulated by PEG-6000 during seed germination and controlled irrigation at seedling and flowering, the DH lines showed better water retention and more robust antioxidant activity. Measurements of physiological parameters (CAT, POD, H2O2, MDA, Fv/Fm) along with analysis of drought-responsive gene expression confirmed the superior drought tolerance of these DH lines. The findings indicate that producing uniform DH lines from distant canola hybrids is an effective strategy to enhance drought tolerance, providing a valuable method for developing stress-tolerance crops.

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 B. napus × B. rapa 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 WRKY28, MYB, LTP, WSP, metallothionein, 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 B. napus and B. rapa exhibit enhanced drought tolerance at both early and reproductive stages. These genotypes represent valuable genetic resources for breeding drought-tolerance canola cultivars.