Evaluation of Brassica root architectural traits

• Author / Creator

  Yang, Chunxiao

• Given the roles of roots in water and nutrient uptake, anchorage, and storage of resources, root system architecture (RSA) can have a major impact on plant growth and development. The root systems of Brassica species, an important group that includes many field and horticultural crops, is complex. Comparative studies of RSA that combine morphological and genetic analyses are limited, particularly because the evaluation of root traits can be tedious and time-consuming. In this thesis, a semi-hydroponic system was optimized for phenotyping RSA traits in Brassica napus, and then utilized for the study of eight RSA traits in a collection of 379 Brassica accessions representing six species (B. napus, B. juncea, B. carinata, B. oleracea, B. nigra and B. rapa). The phenotypic data, assessed with an image analysis system, indicated that B. napus and B. oleracea have the most complex and largest root systems among the species evaluated, with relatively larger values for six of the eight traits measured. In contrast, B. nigra had the smallest root systems. The two species B. juncea and B. carinata shared comparable root system complexity and had thicker root systems compared with the other species. In addition, 313 of the Brassica accessions were genotyped using a 19K Brassica single nucleotide polymorphism (SNP) array. After removing monomorphic and low-coverage site markers, markers with a minor allele frequency (MAF) ≤ 0.05, and those missing data for > 5% of the accessions, a total of 6,213 SNP markers, comprising 5,103 markers on the A genome and 1,110 markers on the C genome, were selected for genome wide association studies (GWAS). These markers effectively covered genomic regions of 302.5 Mb for the A-genome and 452.8 Mb for the C-genome. Four mixed linear models (MLM), and two general linear models (GLM) were tested to identify the genomic regions and SNPs associated with the RSA traits. The GWAS identified 79 significant SNP markers associated with the eight root-related traits under investigation. These markers were distributed across the 18 chromosomes of B. napus, excluding chromosome C06. Sixty-five markers were located on the A-genome, while 14 were found on the C-genome. Furthermore, three specific genomic regions located on chromosomes A02, A03, and A06 were identified as hotspots containing genes associated with root traits. This work paves the way for additional research and exploration of these regions, offering new opportunities to deepen understanding of RSA traits and their genetic basis in the Brassicas.

• Subjects / Keywords

  • Brassica
  • GWAS
  • Root Architecture

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-tq7f-h715

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.