Combining R gene and quantitative resistance increases effectiveness of cultivar resistance against Leptosphaeria maculans in Brassica napus in different environments

Among the Brassica oilseeds, canola (Brassica napus) is the most economically significant globally. However, its production can be limited by blackleg disease, caused by the fungal pathogen Lepstosphaeria maculans. The deployment of resistance genes has been implemented as one of the key strategies to manage the disease. Genetic resistance against blackleg comes in two forms: qualitative resistance, controlled by a single, major resistance gene (R gene), and quantitative resistance (QR), controlled by numerous, small effect loci. R-gene-mediated blackleg resistance has been extensively studied, wherein several genomic regions harbouring R genes against L. maculans have been identified and three of these genes were cloned. These studies advance our understanding of the mechanism of R gene and pathogen avirulence (Avr) gene interaction. Notably, these studies revealed a more complex interaction than originally thought. Advances in genomics help unravel these complexities, providing insights into the genes and genetic factors towards improving blackleg resistance. Here, we aim to discuss the existing R-gene-mediated resistance, make a summary of candidate R genes against the disease, and emphasise the role of players involved in the pathogenicity and resistance. The comprehensive result will allow breeders to improve resistance to L. maculans, thereby increasing yield.

Download Full-text

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

Theoretical and Applied Genetics ◽

10.1007/s00122-021-03877-0 ◽

2021 ◽

Author(s):

Junrey Amas ◽

Robyn Anderson ◽

David Edwards ◽

Wallace Cowling ◽

Jacqueline Batley

Keyword(s):

Brassica Napus ◽

Oilseed Rape ◽

Quantitative Resistance ◽

Crop Improvement ◽

Leptosphaeria Maculans ◽

R Gene ◽

R Genes ◽

Blackleg Resistance ◽

Linkage And Association Analysis ◽

Breeding Programmes

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.

Download Full-text

Assessing Quantitative Resistance against Leptosphaeria maculans (Phoma Stem Canker) in Brassica napus (Oilseed Rape) in Young Plants

PLoS ONE ◽

10.1371/journal.pone.0084924 ◽

2014 ◽

Vol 9 (1) ◽

pp. e84924 ◽

Cited By ~ 23

Author(s):

Yong-Ju Huang ◽

Aiming Qi ◽

Graham J. King ◽

Bruce D. L. Fitt

Keyword(s):

Brassica Napus ◽

Oilseed Rape ◽

Quantitative Resistance ◽

Leptosphaeria Maculans ◽

Stem Canker ◽

Phoma Stem Canker

Download Full-text

Association mapping of quantitative resistance for Leptosphaeria maculans in oilseed rape (Brassica napus L.)

Molecular Breeding ◽

10.1007/s11032-010-9429-x ◽

2010 ◽

Vol 27 (3) ◽

pp. 271-287 ◽

Cited By ~ 49

Author(s):

C. Jestin ◽

M. Lodé ◽

P. Vallée ◽

C. Domin ◽

C. Falentin ◽

...

Keyword(s):

Brassica Napus ◽

Association Mapping ◽

Oilseed Rape ◽

Quantitative Resistance ◽

Leptosphaeria Maculans ◽

Brassica Napus L

Download Full-text

Oilseed rape (Brassica napus) resistance to growth of Leptosphaeria maculans in leaves of young plants contributes to quantitative resistance in stems of adult plants

PLoS ONE ◽

10.1371/journal.pone.0222540 ◽

2019 ◽

Vol 14 (9) ◽

pp. e0222540 ◽

Cited By ~ 2

Author(s):

Yong-Ju Huang ◽

Sophie Paillard ◽

Vinod Kumar ◽

Graham J. King ◽

Bruce D. L. Fitt ◽

...

Keyword(s):

Brassica Napus ◽

Oilseed Rape ◽

Quantitative Resistance ◽

Leptosphaeria Maculans ◽

Adult Plants

Download Full-text

A Cluster of Major Specific Resistance Genes to Leptosphaeria maculans in Brassica napus

Phytopathology ◽

10.1094/phyto.2004.94.6.578 ◽

2004 ◽

Vol 94 (6) ◽

pp. 578-583 ◽

Cited By ~ 101

Author(s):

R. Delourme ◽

M. L. Pilet-Nayel ◽

M. Archipiano ◽

R. Horvais ◽

X. Tanguy ◽

...

Keyword(s):

Brassica Napus ◽

Resistance Genes ◽

Specific Resistance ◽

Quantitative Resistance ◽

Specific Interaction ◽

Leptosphaeria Maculans ◽

Field Resistance ◽

Genetic Identification ◽

Adult Plant ◽

Avirulence Genes

Two types of genetic resistance to Leptosphaeria maculans usually are distinguished in Brassica napus: qualitative, total resistance expressed at the seedling stage and quantitative, partial resistance expressed at the adult plant stage. The latter is under the control of many genetic factors that have been mapped through quantitative trait loci (QTL) studies using ‘Darmor’ resistance. The former usually is ascribed to race-specific resistance controlled by single resistance to L. maculans (Rlm) genes. Three B. napus-originating specific Rlm genes (Rlm1, Rlm2, and Rlm4) previously were characterized. Here, we report on the genetic identification of two novel resistance genes, Rlm3 and Rlm7, corresponding to the avirulence genes AvrLm3 and AvrLm7. The identification of a novel L. maculans- B. napus specific interaction allowed the detection of another putative new specific resistance gene, Rlm9. The resistance genes were mapped in two genomic regions on LG10 and LG16 linkage groups. A cluster of five resistance genes (Rlm1, Rlm3, Rlm4, Rlm7, and Rlm9) was strongly suggested on LG10. The relation between all these specific resistance genes and their potential role in adult-plant field resistance is discussed. These two Rlm-carrying regions do not correspond to major QTL for Darmor quantitative resistance.

Download Full-text

Comparison of non-subjective relative fungal biomass measurements to quantify the Leptosphaeria maculans—Brassica napus interaction

Plant Methods ◽

10.1186/s13007-021-00822-6 ◽

2021 ◽

Vol 17 (1) ◽

Author(s):

Wendelin Schnippenkoetter ◽

Mohammad Hoque ◽

Rebecca Maher ◽

Angela Van de Wouw ◽

Phillip Hands ◽

...

Keyword(s):

Brassica Napus ◽

Fungal Pathogen ◽

Fungal Biomass ◽

Quantitative Resistance ◽

Leptosphaeria Maculans ◽

Post Inoculation ◽

Blackleg Disease ◽

In Planta ◽

Visual Assessments ◽

Host Tissues

Abstract Background Blackleg disease, caused by the fungal pathogen Leptosphaeria maculans, is a serious threat to canola (Brassica napus) production worldwide. Quantitative resistance to this disease is a highly desirable trait but is difficult to precisely phenotype. Visual scores can be subjective and are prone to assessor bias. Methods to assess variation in quantitative resistance more accurately were developed based on quantifying in planta fungal biomass, including the Wheat Germ Agglutinin Chitin Assay (WAC), qPCR and ddPCR assays. Results Disease assays were conducted by inoculating a range of canola cultivars with L. maculans isolates in glasshouse experiments and assessing fungal biomass in cotyledons, petioles and stem tissue harvested at different timepoints post-inoculation. PCR and WAC assay results were well correlated, repeatable across experiments and host tissues, and able to differentiate fungal biomass in different host-isolate treatments. In addition, the ddPCR assay was shown to differentiate between L. maculans isolates. Conclusions The ddPCR assay is more sensitive in detecting pathogens and more adaptable to high-throughput methods by using robotic systems than the WAC assay. Overall, these methods proved accurate and non-subjective, providing alternatives to visual assessments to quantify the L. maculans-B. napus interaction in all plant tissues throughout the progression of the disease in seedlings and mature plants and have potential for fine-scale blackleg resistance phenotyping in canola.

Download Full-text