Junrey Amas, Robyn Anderson, David Edwards, Wallace Cowling & Jacqueline Batley

Theoretical and Applied Genetics October 2021; vol. 134:3123–3145

Key message

Quantitative resistance (QR) loci discovered through genetic and genomic analyses are abundant in the Brassica napus genome, providing an opportunity for their utilization in enhancing blackleg resistance.

Abstract

Quantitative resistance (QR) has long been utilized to manage blackleg in Brassica napus (canola, oilseed rape), even before major resistance genes (R-genes) were extensively explored in breeding programmes. In contrast to R-gene-mediated qualitative resistance, QR reduces blackleg symptoms rather than completely eliminating the disease. As a polygenic trait, QR is controlled by numerous genes with modest effects, which exerts less pressure on the pathogen to evolve; hence, its effectiveness is more durable compared to R-gene-mediated resistance. Furthermore, combining QR with major R-genes has been shown to enhance resistance against diseases in important crops, including oilseed rape. For these reasons, there has been a renewed interest among breeders in utilizing QR in crop improvement. However, the mechanisms governing QR are largely unknown, limiting its deployment. Advances in genomics are facilitating the dissection of the genetic and molecular underpinnings of QR, resulting in the discovery of several loci and genes that can be potentially deployed to enhance blackleg resistance. Here, we summarize the efforts undertaken to identify blackleg QR loci in oilseed rape using linkage and association analysis. We update the knowledge on the possible mechanisms governing QR and the advances in searching for the underlying genes. Lastly, we lay out strategies to accelerate the genetic improvement of blackleg QR in oilseed rape using improved phenotyping approaches and genomic prediction tools.

See: https://link.springer.com/article/10.1007/s00122-021-03877-0

Figure 1: Circos plot displaying the physical position (Mbp) of QTLs and significant genomic regions for blackleg QR in the Brassica napus genome (Darmor v4.1). Shown in green highlight are QTL based from Darmor-derived populations (a. Pilet et al. 1998; b. Pilet et al 2001; c. Delourme et al. 2008; d. Jestin et al. 2015; e. Huang et al. 2016; f. Kumar et al. 2018; g. Raman et al. 2018; h. Huang et al. 2019); in red are QTL from non-Darmor populations (i. Larkan et al. 2016; j. Raman et al. 2020a); while in orange are marker positions based from genome-wide association studies (GWAS) (k. Fopa Fomeju et al. 2014; l. Raman et al. 2016; m. Kumar et al. 2018; n. Raman et al. 2020b; o. Fikere et al. 2020a, b). Only studies that disclosed marker sequence information and hence can be mapped to Darmor v4.1 reference genome were included in the diagram.