Muhammad Jakir Hasan | ALES Graduate Seminar

Date(s) - 04/08/2021
9:00 am - 10:00 am

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 Muhammad Jakir Hasan. This seminar is open to the general public to attend.
Meeting ID: 920 1570 4886 | Passcode: 101083
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Thesis Topic: Genetics of clubroot disease (Plasmodiophora brassicae) resistance in Brassica

PhD with Dr. Habib Rahman.

Seminar Abstract:

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 belongs to allopolyploid Brassica napus L. (AACC genome, 2n = 38) and B. juncea L. (AABB genome, 2n=36), is an important oilseed crop in the world. Natural 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 its allied species and diploid progenitor species.

In this study, the genetic control of clubroot disease resistance of 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. One doubled haploid (DH) population developed from B. napus var. napobrassica cv. Brookfield (rutabaga) × B. napus spring canola, a recombinant inbred line (RIL) population developed from B. napus spring canola × B. rapa var. pekinensis cv. Bilko (Chinese cabbage) interspecific cross and synthetic B. juncea lines developed from B. rapa var. rapifera cvGelria (turnip) × B. nigra interspecific cross was used. The DH, RIL, and synthetic lines were phenotyped for resistance to several P. brassicae pathotypes and genotyped using SSR and SNP-based (Allele-Specific) AS-markers and KASP (Kompetitive allele-specific PCR) to map clubroot resistant (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 population indicated that major gene control clubroot resistance. Genetic analysis using the DH lines identified a genomic region, qCR_A8, on chromosome A08 of rutabaga cv. Brookfield is associated with resistance to P. brassicae pathotypes 2, 3, 5, 6, and 8 and a locus, qCR_A3, on chromosome A03 associated with resistance to pathotype 3. The QTL analysis indicated that rutabaga cv. Brookfield carries a high oil QTL, qOIL­_C3, around 15 cM away from a major erucic acid QTL on chromosome C03 and a major QTL on chromosome A02 affecting both vernalization and flowering time. 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 poor agronomic and seed quality traits. The genetic analysis of the RIL population indicated introgression of a CR locus from chromosome A03 of the Chinese cabbage cv. Bilko into 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, e.g., qCR_A8 and Bilko-CR, 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 of this thesis research provided substantial evidence that (a) rutabaga and the Chinese cabbage gene pool can be used to broaden the genetic base for clubroot resistance in B. napus canola, (b) rutabaga carries favourable alleles for flowering and seed quality traits and (c) clubroot resistance of rutabaga cv. Brookfield does not carry linkage drag for poor 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 (d) the clubroot resistant B. juncea line can be developed by exploiting the resistance available in B. rapa.