Selvaraj: Building Durable Clubroot Resistance in Canola: Identification of Multiple Clubroot Resistance Genes From Brassica Napus and B. Rapa for Marker-Assisted Gene Stacking in Canola Breeding
Date: November 2015
Term: n/a
Status: Completed
Researcher(s): Gopalan Selvaraj and Manoj Kulkarni, National Research Council, Saskatoon SK, Habibur Rahman, University of Alberta, Edmonton AB
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: WGRF, ADF
Project Summary
Clubroot is a serious soil-borne disease of canola caused by the pathogen Plasmodiophora brassicae. Multiple genes that can be clearly identified and stacked or rotated are required for long-term effectiveness of clubroot management toward protecting canola yield. The objectives of this study were to identify, map and characterize clubroot resistance genes using genetic linkage mapping, transcriptome analysis and small RNA analysis. Researchers identified and mapped a tightly linked marker for clubroot resistance that will be useful to canola breeders to introduce clubroot resistant genes into modern cultivars as a proactive measure to mitigate breakdown of resistance. Disease resistance genes identified in this project can be validated and stacked for durable clubroot resistance.
Clubroot is a serious soil-borne disease of canola caused by the pathogen Plasmodiophora brassicae. The spores can survive in soil for many years, making the disease an ongoing threat. Although varieties with some degree of resistance are now available, their genetic make-up is unknown. The resistance afforded by resistance (R) genes must be durable so that pathogens cannot outpace the host and overcome the resistance. Multiple genes that can be clearly identified and stacked or rotated are required for long-term effectiveness of clubroot management toward protecting canola yield.
The goal of this study was to find the genes that can be associated with disease resistance in Brassica napus so that resistance genes can be used judiciously to build durable resistance. Of the many different pathotypes of P. brassicae, researchers focused on P3, which is very virulent and currently the most significant pathotype in western Canada. The objectives of the study were to take a multidisciplinary approach to identify, map and characterize clubroot resistance genes.
For the study, researchers used populations resulting from a genetic cross of 'Mendel', a European winter rapeseed variety, with two susceptible spring B. napus canola lines. Ninety-four double haploid (DH) lines from each cross comprised the study population used to identify genomic regions associated with resistance. Project experiments included genetic linkage mapping, transcriptome analysis and small RNA analysis.
The genetic linkage mapping resulted in the identification of a major locus for clubroot resistance in spring canola (B. napus), which was mapped and a marker identified. This tightly linked marker for resistance, derived from Mendel, a European winter rapeseed, can be further used for Marker Assisted Selection in the future, and can be stacked with other known clubroot resistance loci on other chromosomes (like A1, A8) to breed stronger resistance. This locus alone only contributes about 50% genetic variation for clubroot resistance, indicating the need to find other resistance factors that cannot be identified by genetic linkage mapping alone. Because this locus is molecularly complex, the multiplicity of resistance gene-like sequences needs to be investigated further to determine if a single protein-coding gene is responsible or if interactions with other gene(s) in the proximity are required.
From the results of the transcriptome analysis, researchers generated a comprehensive atlas of susceptibility and resistance reactions at the primary, secondary and maturation phase of clubroot disease, which provides a valuable starting point to analyze the ancillary resistance pathways. A further investigation is needed to present a prioritized list of genes for selection and transferring stronger resistance to target varieties.
Researchers also performed small RNA sequencing and analysis to identify small RNA categories expressed at a higher level in resistance reaction. These were mapped to the B. napus genome and the differential response for the primary, secondary and maturity phases of disease progression identified in susceptible and resistant canola. This analysis can be used in assembling additional arsenal for combating the disease by genetics.
The study results will be useful to canola breeders to introduce clubroot resistant genes into modern cultivars, which may then be used in rotations as a proactive measure to mitigate breakdown of resistance. Disease resistance genes identified in this project can be validated and stacked for durable clubroot resistance. Future research needs to be done to identify how clubroot resistance genomic regions, transcriptome and small RNA interplay with clubroot resistance and susceptibility response.
Scientific Publications
Sharma et al., (2013). Reaction of Lines of the Rapid Cycling Brassica Collection and Arabidopsis thaliana to Four Pathotypes of Plasmodiophora brassicae. Plant Disease 97:6, 720-727.
Rahman H., Peng G., Yu F., Falk K.C., Kulkarni M., & Selvaraj G. (2013). Genetics and breeding for clubroot resistance in Canadian spring canola (B. napus L.). Canadian Journal of Plant Pathology special issue for clubroot resistance.36 (s1):122-134 DOl:10.1080/07060661.2013.862571