Dissection of Quantitative Blackleg Resistance Reveals Novel Variants of Resistance Gene Rlm9 in Elite Brassica napus

• Published in: Frontiers in plant science Vol. 12; p. 749491
• Main Authors: Vollrath, Paul, Chawla, Harmeet S, Alnajar, Dima, Gabur, Iulian, Lee, HueyTyng, Weber, Sven, Ehrig, Lennard, Koopmann, Birger, Snowdon, Rod J, Obermeier, Christian
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 18-11-2021
• Subjects: blackleg; Brassica napus; long-read sequencing; ONT; Plant Science; Rlm9; structural variation; Rlm9; blackleg; Brassica napus; structural variation; ONT; long-read sequencing
• ISSN: 1664-462X; 1664-462X
• DOI: 10.3389/fpls.2021.749491

Blackleg is one of the major fungal diseases in oilseed rape/canola worldwide. Most commercial cultivars carry
gene-mediated qualitative resistances that confer a high level of race-specific protection against
, the causal fungus of blackleg disease. However, monogenic resistances of this kind can potentially be rapidly overcome by mutations in the pathogen's avirulence genes. To counteract pathogen adaptation in this evolutionary arms race, there is a tremendous demand for quantitative background resistance to enhance durability and efficacy of blackleg resistance in oilseed rape. In this study, we characterized genomic regions contributing to quantitative
resistance by genome-wide association studies in a multiparental mapping population derived from six parental elite varieties exhibiting quantitative resistance, which were all crossed to one common susceptible parental elite variety. Resistance was screened using a fungal isolate with no corresponding avirulence (
) to major
genes present in the parents of the mapping population. Genome-wide association studies revealed eight significantly associated quantitative trait loci (QTL) on chromosomes A07 and A09, with small effects explaining 3-6% of the phenotypic variance. Unexpectedly, the qualitative blackleg resistance gene
was found to be located within a resistance-associated haploblock on chromosome A07. Furthermore, long-range sequence data spanning this haploblock revealed high levels of single-nucleotide and structural variants within the
coding sequence among the parents of the mapping population. The results suggest that novel variants of
could play a previously unknown role in expression of quantitative disease resistance in oilseed rape.