Abstract
Leptosphaeria maculans causes blackleg disease in Brassica napus. The blackleg disease is mainly controlled by resistance genes in B. napus. Previous studies have shown that the blackleg resistant BLMR2 locus that conferred horizontal resistance under field conditions, is located on chromosome A10 of B. napus. The purpose of this study is to fine map this locus and hence identify a candidate gene underlying horizontal resistance. The spectrum of resistance to L. maculans isolates of the resistance locus BLMR2 was analyzed using near isogenic lines, resistant, and susceptible cultivars. The results showed that this locus was horizontally resistant to all isolates tested. Sequence characterized amplified regions (SCAR), simple sequence repeats (SSR), and single nucleotide polymorphism (SNP) markers were developed in the chromosome region of BLMR2 and a fine genetic map was constructed. Two molecular markers narrowed BLMR2 in a 53.37 kb region where six genes were annotated. Among the six annotated genes, BnaA10g11280D/BnaA10g11290D encoding a cytochrome P450 protein were predicted as the candidate of BLMR2. Based on the profiling of pathogen induced transcriptome, three expressed genes in the six annotated genes were identified while only cytochrome P450 showed upregulation. The candidate corresponds to the gene involved in the indole glucosinolate biosynthesis pathway and plant basal defense in Arabidopsis thaliana. The molecular markers identified in this study will allow the quick incorporation of the BLMR2 allele in rapeseed cultivars to enhance blackleg resistance.
Highlights
Brassica napus is an important crop used for edible oil production worldwide
In the BC4 mapping population of 831 individuals, there were 438 resistant plants and 393 susceptible plants showing a 1:1 segregation ratio (χ2 test, p > 0.05), suggesting that one dominant resistance allele is responsible for the BLMR2 resistance to blackleg (Figure 1)
Our results suggest that CYP450 possibly plays a role in L. maculans induced defense response in B. napus
Summary
Brassica napus (oilseed rape/canola) is an important crop used for edible oil production worldwide. Blackleg, caused by Leptosphaeria maculans, is one of the most devastating diseases in B. napus (canola, oilseed, and rapeseed) production. There are both qualitative and quantitative types of resistance to fungal pathogens like L. maculans (Rouxel et al, 2003; Raman et al, 2012, 2013). Quantitative resistance or horizontal resistance is race non-specific, which may be mediated by several genes and expressed from the seedling to adult plant stages, conferring only partial resistance to all races of the pathogen (Delourme et al, 2006; Rimmer, 2006). Identification and incorporation of resistance genes in Brassica species to produce resistant cultivars is an efficient approach to combat blackleg disease in B. napus (Hayward et al, 2012)
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