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Understanding major gene-mediated resistance in Brassica napus (oilseed rape) against the apoplastic fungal pathogen, Pyrenopeziza brassicae

Chinthani Karandeni-Dewage: University of Hertfordshire

<div>Light leaf spot disease, caused by the fungal pathogen, <em>Pyrenopeziza brassicae</em>, is currently the most damaging foliar disease on winter oilseed rape (<em>Brassica napus</em>) in the UK. Light leaf spot disease management is often reliant on fungicide applications. However, there has been evidence for the development of insensitivity to azole fungicides in UK <em>P. brassicae</em> populations. Deployment of cultivar resistance remains an important aspect of effective management of the disease. Nevertheless, the genetic basis of resistance remains poorly understood and no resistance genes have been cloned. A major gene locus (<em>PBR2</em>) for resistance against <em>P. brassicae</em> has been mapped to the bottom end of the <em>B. napus</em> chrA01 c. 3.0 cM away from the closest flanking marker. We have identified the physical location of the closest flanking marker on <em>B. napus</em> chrA01 using synteny alignment between<em> B. napus</em> and <em>B. rapa </em>chrA01. The interval between this locus and the telomere corresponds to a c. 1.2Mbp region in chrA01. Single nucleotide polymorphism (SNP) markers on the corresponding genomic region have been obtained and c. 400 candidate SNPs specific to chrA01 have been identified. Further analysis of this region was done through fine mapping of selected SNPs using KASP marker analysis. As a result, three additional markers linked to the resistance locus were identified, which narrowed down the corresponding chromosomal region to c. 300Kbp. It is expected that this fine mapping will provide tightly linked markers for marker-assisted selection and assist in the isolation, sequencing and functional identification of the resistance gene.</div>