Defining populations of Plasmodiophora brassicae with near isogenic Brassica napus lines
Date: April, 2022
Term: 5 years
Status: Complete
Researcher(s): Fengqun Yu, Yan Zhang and Jinghe Wang, Agriculture and Agri-Food Canada, Saskatoon
SaskCanola Investment: $71,125
Total Project Cost: $284,400
Funding Partners: Agriculture Development Fund
Grower Benefits
Researchers have developed canola lines with a broad spectrum of clubroot resistance derived from three sources of turnips, which are very valuable for developing resistant cultivars by canola breeders.
The first set of Brassica napus near isogenic lines (NIL), each containing one of eight single clubroot resistant (CR) genes, has been developed, which could replace the current Canadian Clubroot Differential set and also monitor race change in the pathogen race structure. This could potentially revolutionize the clubroot pathotyping systems currently used around the world.
More than 1,200 doubled haploid (DH) lines have been developed in the project that can serve as ideal materials for identification of novel resistant genes. As the pathogen evolves, new emerging races of the pathogen can be identified in canola fields on the Prairies.
Several breeding lines have been distributed to AAFC Clubroot Consortium members for development of future clubroot resistant canola cultivars.
Project Description
Genetic resistance can be an effective strategy for clubroot management, but the sources available for resistance to clubroot disease caused by Plasmodiophora brassicae in Brassica napus are very limited. Building on previous research, the objectives of this project were to complete the development of the doubled haploid (DH) lines, develop a set of near isogenic spring type B. napus lines and define populations of P. brassicae collected in western Canada. As a result of the project, researchers have developed canola lines with a broad spectrum of clubroot resistance derived from three sources of turnips, developed more than 1200 DH lines for identification of novel resistant genes and produced the first set of near isogenic lines, each containing one of eight single CR genes in brassica crops. These lines could replace the current Canadian Clubroot Differential set and monitor race change in the pathogen race structure, potentially revolutionizing the clubroot pathotyping systems around the world.
For canola growers, clubroot disease caused by Plasmodiophora brassicae continues to pose a serious threat to canola production, not only in western Canada but worldwide. Genetic resistance can be an effective strategy for clubroot management, but the sources available for resistance to clubroot in Brassica napus are very limited.
Building on previous research, the objectives of this project were to complete the development of the doubled haploid (DH) lines initiated in a previous project, develop a set of near isogenic spring type B. napus lines (NILs) carrying resistance and define populations of P. brassicae collected in western Canada. Conventional breeding methods such as crossing and backcrossing, and molecular marker-assisted selection (MAS) were used in this project. Next generation sequencing technologies were used for genetic mapping of clubroot resistance (CR) genes, which has greatly accelerated CR gene identification.
Researchers performed genetic mapping in several DH populations with introgressed CR genes from B. rapa turnips, resulting in the identification of four novel genes at the Rcr9 locus and one gene at the Rcr10 locus. They also identified a gene at the RcrM locus from two mapping populations, one from European canola cv. ‘Mendel’ and a second from introgressed B. napus lines originating from turnip cv. ‘Siloga’. This resulted in the development of canola DH lines with a broad spectrum of clubroot resistance derived from three sources of turnips. The resulting DH lines, which were distributed to AAFC Clubroot Consortium members in April 2021, showed a high level of resistance to the majority of Canadian races of the clubroot pathogen identified in this study. These lines are very valuable for developing resistant cultivars by canola breeders and for more robust strategies for disease management in the future.
Researchers also developed a set of B. napus near-isogenic lines (NILs) containing single CR genes, which is ideal for differentiating races of P. brassica. This first set of NILs containing eight single CR genes in brassica crops could replace the current Canadian Clubroot Differential set and also be used for monitoring changes in the pathogen populations in canola fields. The NILs can be used for genetic studies on the pathogen such as identification and cloning of the potential Avr genes, developing SNP markers associated with each of the Avr genes and providing information concerning the effectiveness of resistance.
In the study, researchers obtained more than 1200 doubled haploid (DH) lines derived from BC2 to BC4 donor plants with clubroot resistance from one B. napus and seven B. rapa cultivars. Selection was carried out by testing clubroot resistance to strains collected in western Canada and evaluating morphological traits under greenhouse and field conditions. One field trial consisting of 340 lines with single rows of each test entry was conducted at AAFC Saskatoon Research Farm in 2020 to select lines with acceptable days to flowering and development. Only a small amount of seeds for each line have been produced, and a field trial for increasing seeds will be performed in 2022. These DH populations can serve as ideal materials for identification of novel resistant genes. For example, as the pathogen evolves, new emerging races of the pathogen can be identified in the canola fields on the Prairie.
Clubroot strains for the study were collected in canola fields in Alberta, Saskatchewan, and Manitoba to define populations of P. brassicae in western Canada. Dr. Yu's group developed a highly efficient method for testing plants for resistance to clubroot that was used in the study. A total of 76 strains were obtained with 36 successfully propagated in canola line DH16516. These 36 strains were classified into 28 races, indicating there are very diverse races on canola fields in western Canada. Researchers also found that lines with more than one CR gene exhibited strong resistance to 34 or 35 out of the 36 strains of P. brassicae.
Overall, the project has resulted in the development of canola lines with a broad spectrum of clubroot resistance derived from three sources of turnips. Researchers also developed more than 1200 DH lines for identification of novel resistant genes and produced the first set of near isogenic lines containing eight single CR genes in brassica crops. These lines could replace the current Canadian Clubroot Differential set and monitor race change in the pathogen race structure, potentially revolutionizing current clubroot pathotyping systems. Several breeding lines have been distributed to AAFC Clubroot Consortium members for development of future clubroot resistant canola cultivars.
Scientific Publications:
Yu F, Zhang Y, Wang J, Chen Q, Karim M, Gossen BD, Peng G (2022) Identification of two major QTLs in Brassica napus lines with introgressed clubroot resistance from turnip cultivar ECD01. Front. Plant Sci. https://www.frontiersin.org/articles/10.3389/fpls.2021.785989/full