Status and advances in mining for blackleg (Leptosphaeria maculans) quantitative resistance (QR) in oilseed rape (Brassica napus)

Abstract

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.

Understanding the Proteomes of Plant Development and Stress Responses in Brassica Crops

“…The proteomics approach has also been used in various studies to explain the interaction between plants and fungi belonging to the biotrophic (feeding on living tissue) and necrotrophic (feeding on dead tissue) groups. Various fungal pathogens have been explored for studying these interactions, like Albugo candida , Leptosphaeria maculans , Plasmodiophora brassicae , Sclerotinia sclerotiorum , and Verticillium longisporum with various species of Brassicas including B. juncea , B. napus, B. oleracea, B. carinata , and B. rapa . − …”

Harnessing adult-plant resistance genes to deploy durable disease resistance in crops

“…In addition to resistance against biotrophic fungi, such as rust and powdery mildew, studies have reported the involvement of APR genes in resistance against hemibiotrophic and necrotrophic diseases, such as tan spot [ 27 ], Septoria nodorum blotch [ 28 ] and Fusarium head blight/crown rot [ 29 ] of wheat. Outside the cereals, APR genes are also known globally for their involvement in resistance against important diseases of other crops, such as maize northern leaf spot [ 30 ], canola blackleg [ 31 ], Brassica downy mildew [ 32 ], chickpea Fusarium wilt and Ascochyta blight [ 33 ], and soybean powdery mildew [ 34 ]. Beside conveying resistance against multiple pathogen strains, these APR genes play a vital role in prolonging the durability of frequently used major or seedling resistance genes when deployed along with them.…”

“…Although the QTLs or genomic regions conferring these resistance traits have been identified through GWAS and comparative genomic analysis, many of the underlying causal genes are unknown. This hampers our ability to unravel the underlying molecular mechanisms of these high-value resistance genes [ 31 ]. Only in the case of maize, the APR gene Helminthosporium maydis (Hm)1 for northern leaf spot was identified to encode an NADPH-dependent reductase.…”

Understanding R Gene Evolution in Brassica

“…It has been shown that climate changes, such as variation in the CO 2 concentration, temperature fluctuations and water availability, play a role in influencing disease outcomes in host plants [61]. Disease severity is also impacted by the type of disease resistance of the host, whether it is qualitative or quantitative; in Brassica blackleg disease [62][63][64][65][66][67][68], or in the qualitative type, it depends on the specific pathotype that infects the host. For example, in the B. napus-Pyrenopeziza brassicae (light leaf spot) interaction, the host resistance is specific to the isolated pathotypes [69].…”