Abstract
Drought stress can directly inhibit seedling establishment in canola (Brassica napus), resulting in lower plant densities and reduced yields. To dissect this complex trait, 140 B. napus accessions were phenotyped under normal (0.0 MPa, S0) and water-stressed conditions simulated by polyethylene glycol (PEG) 6000 (−0.5 MPa, S5) in a hydroponic system. Phenotypic variation and heritability indicated that the root to shoot length ratio was a reliable indicator for water stress tolerance. Thereafter, 66 accessions (16 water stress tolerant, 34 moderate and 16 sensitive lines) were genotyped using 25,495 Brassica single nucleotide polymorphisms (SNPs). Genome-wide association studies (GWAS) identified 16 loci significantly associated with water stress response. Two B. napus accessions were used for RNA sequencing, with differentially-expressed genes under normal and water-stressed conditions examined. By combining differentially-expressed genes detected by RNA sequencing with significantly associated loci from GWAS, 79 candidate genes were identified, of which eight were putatively associated with drought tolerance based on gene ontology of Arabidopsis. Functional validation of these genes may confirm key drought-related genes for selection and breeding in B. napus. Our results provide insight into the genetic basis of water stress tolerance in canola.
Highlights
Canola (Brassica napus) is one of the largest oil crops in the world together with soybean and oil palm
Root length (RL) and R/S significantly increased by 14.3% and 91.0%, respectively, but shoot length (SL) and Fresh weight (FW) significantly decreased by 40.1% and 60.1%, respectively, compared to the control (Table 1)
Relative to the average variation of all measured traits under normal conditions, variation in RL and R/S increased while variation in SL and FW decreased under water stress conditions (Figure 1)
Summary
Canola (Brassica napus) is one of the largest oil crops in the world together with soybean and oil palm. It is very sensitive to drought stress, a major yield-limiting factor in this crop (Wan et al, 2009). Drought stress can directly inhibit seedling establishment, resulting in lower plant densities and reduced yields. Increased drought conditions are predicted worldwide due to the predicted long-term effects of global climate change (Cook et al, 2007). An important solution to this challenge is the development of canola cultivars which can tolerate water stress in order to maintain oil production. A key step toward genomics-assisted breeding for water stress tolerance
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