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Genetics of clubroot (Plasmodiophora brassicae) disease resistance in Brassica
- Author / Creator
- Hasan, Muhammad J
Clubroot disease, caused by Plasmodiophora brassicae, is a major threat to canola production. Cultivation of resistant cultivars is the key component in managing this disease. Canola is an important oilseed crop in the world; this includes the allopolyploid species Brassica napus L. (AACC genome, 2n = 38) and B. juncea L. (AABB genome, 2n = 36) and the diploid species B. rapa L. (AA, 2n = 20). Oilseed B. napus and B. juncea lack resistance to clubroot disease; therefore, there is a need to introduce resistance to this disease in canola from diverse sources including its progenitor species.
In this study, the genetic control of clubroot disease resistance in the polyploid B. napus var. napobrassica and diploid B. rapa vars. pekinensis and rapifera were investigated for resistance in B. napus canola and for the development of clubroot resistant B. juncea. Doubled haploid (DH) and recombinant inbred line (RIL) populations developed from B. napus var. napobrassica cv. Brookfield (rutabaga) × B. napus spring canola and B. napus spring canola × B. rapa var. pekinensis cv. Bilko (Chinese cabbage) interspecific crosses and synthetic B. juncea lines developed from B. rapa var. rapifera cv. Gelria (turnip) × B. nigra interspecific cross was used in this study. These populations were phenotyped for resistance to several P. brassicae pathotypes and genotyped using SSR and SNP-based allele-specific (AS) and KASP (Kompetitive allele-specific PCR) markers to map the clubroot resistance (CR) loci and develop genetic markers. The DH lines were also evaluated in replicated field trials for QTL mapping of flowering and seed quality traits.
Analysis of the DH and RIL populations indicated that a major gene controls clubroot resistance in the rutabaga cv. Brookfield. Genetic analysis using the DH lines identified a genomic region, qCRA8, on chromosome A08 is associated with resistance to P. brassicae pathotypes 2, 3, 5, 6, and 8, and a locus, qCRA3, on chromosome A03 associated with resistance to pathotype 3. QTL analysis indicated that the rutabaga cv. Brookfield carries a high oil QTL, qOIL¬C3, about 15 cM away from a major erucic acid QTL on chromosome C03 and a major QTL on chromosome A02 affects both vernalization requirement and flowering time variation. The qOIL¬C3 could increase oil content in spring canola by about 0.7%. Further analysis exhibited no correlation of clubroot resistance of rutabaga cv. Brookfield, with agronomic and seed quality traits. Genetic analysis of the canola × Chinese cabbage RIL population demonstrated that introgression of a CR locus from the Chinese cabbage cv. Bilko occurred into chromosome A03 of spring B. napus canola. The Bilko-CR locus co-segregated with the AS-markers in the homozygous RIL families. However, recombination between the CR loci and their co-segregating markers indicated that the genetic markers developed in this research might not be located within the CR genes; the allelic variation exhibited by the markers may not be due to the variation in sequence motifs affecting the phenotypic variation.
Analysis of the synthetic B. juncea lines using A- and B-genome specific SSR markers and their reaction to P. brassicae pathotype 3 indicated that clubroot resistant B. juncea line could be developed by exploiting the resistance available in B. rapa. However, a loss of resistance in around 5.8% of the resynthesized S2 B. juncea plants indicated that the genomic regions carrying the CR could be in a state of genomic change.
Thus, the results from this thesis research provided substantial evidence that rutabaga and the Chinese cabbage gene pool can be used to broaden the genetic base for clubroot resistance in B. napus canola. Rutabaga also carries favourable alleles for seed oil content. The clubroot resistance of this rutabaga cultivar does not exert any negative effect on agronomic and seed quality traits; thus, this resistance can safely be used in canola breeding. The results from this Ph.D. thesis research also provide evidence that clubroot-resistant B. juncea can be developed by exploiting the resistance available in B. rapa.
- Graduation date
- Fall 2021
- Type of Item
- Doctor of Philosophy
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