3:00 pm - 4:00 pm
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Md Mizanur Rahaman. This seminar is open to the general public to attend.
Thesis Topic: Identification and genetic mapping of resistance genes against Canadian pathotypes of Plasmodiophora brassicae in Brassica rapa and Brassica napus
PhD with Drs. Stephen Strelkov and Fengqun Yu.
Clubroot, caused by Plasmodiophora brassicae, is an important soilborne disease of canola/rapeseed (Brassica napus) and other cruciferous crops. In this study, clubroot resistance loci/genes effective against P. brassicae pathotypes 2B, 3A, 3D, 3H, 5C, 5X and 8J were identified and mapped via genotyping-by-sequencing (GBS), QTL analysis, and conventional linkage mapping. Four of 34 B. napus accessions, CGN06902, CGN17369, CGN18957, and CN46235, were found to be resistant to pathotypes 3A, 2B, and 3D, developing disease severity indices ranging from 0% ± 0.0% to 46.3% ± 7.4%. The resistant accession CGN18957 (‘Bristol’), B. napus cv.‘Mendel’, and B. rapa line ECD02 were used to map resistance genes by developing a BC1S1 population based on ECD02 and doubled haploid (DH) populations based on ‘Bristol’ and ‘Mendel’. A single QTL Rcr9ECD02 was identified on chromosome A08 of B. rapa ECD02 using 93 BC1S1 lines; this QTL conferred resistance to pathotypes 3A, 3D, 3H, and 5X, explaining 68.9-74.4% of the phenotypic variation explained (PVE). Bulked segregant and KASP analysis confirmed the QTL. In B. napus ‘Bristol’, a QTL Rcr9Bristol was identified on chromosome A08 using 102 DH lines; Rcr9Bristol explained 92.6-95.0% of the total PVE in response to pathotypes 3A, 3D, 3H, and 5X, with LOD values of 60.3 to 70.8. In ‘Mendel’, the QTL Rcr3Mendel was mapped on chromosome A08 using 137 DH lines; this was a major locus that explained 88-90% of the PVE for resistance to pathotypes 3D, 5C, and 8J with an additive effect of 47.2-47.3%. Testing of a subset of this population (60 lines) against pathotype 3H indicated that Rcr3Mendel is the Rcr3 locus, but that it also bestows resistance to pathotypes 3D, 5C, and 8J. The TIR_NBS_LRR (TNL) genes identified in the QTL regions of the three populations confirmed that the identified QTL Rcr9ECD02, Rcr9Bristol and Rcr3Mendel are different from each other and also distinct from the QTL Rcr9. The CR loci/genes and germplasm identified in this study will serve to enrich the clubroot resistance gene repository, helping to protect canola/oilseed rape production from the damaging effects of clubroot disease.