Azam Nikzad | ALES Graduate Seminar

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 Azam Nikzad. This seminar is open to the general public to attend.

Thesis Topic: Potential of the Brassica oleracea gene pool for the improvement of spring B. napus canola

PhD with Dr. Habibur Rahman.

Seminar Abstract:

Canola (Brassica napus L.) is an amphidiploid or allotetraploid (AACC, 2n = 4x = 38) crop plant and it is one of the most important oilseed crops in the world. The narrow genetic base of this crop, especially in its C genome, is not only a major impediment for its continued improvement but also for mapping and identification of all loci and alleles for a trait that could be found in the Brassica genomes. Currently, hybrid canola cultivars have taken the majority of market share in different countries including Canada. To increase the yield of hybrid canola, there is a need for increasing the level of heterosis or hybrid vigor in this type of cultivar for which presence of adequate genetic diversity in hybrid parental lines is needed. In this study, the value of the C genome of six B. oleracea L. (CC, 2n = 18) accessions belonging to four variants of this species, viz. vars. alboglabra, botrytis, capitata and italica, was investigated for broadening the genetic base of spring B. napus canola. Six B. napus canola inbred populations developed from six B. napus × B. oleracea interspecific crosses and two breeding methods (F₂– and BC₁-derived inbred lines) were used. Test hybrids were produced by crossing the inbred lines to the B. napus canola line and the inbred and test hybrid populations were evaluated in replicated field trials for different agronomic and seed quality traits including yield. Inbred lines were also analyzed by SSR and SNP markers to assess genetic diversity of the inbred populations and the effect of the C genome alleles in the inbred and hybrid populations as well as for QTL mapping of different traits.

Analysis of the parents and the inbred populations using 95 SSR markers showed the existence of wide diversity among the B. oleracea accessions; several canola lines derived from the six crosses tended to group together with their B. oleracea parent demonstrating that the diversity of the B. oleracea gene pool can be exploited for broadening the genetic base of the C genome of B. napus canola. However, loss of some B. oleracea alleles occurred in the inbred populations during the development of these lines and this loss occurred to a greater extent in the F₂-derived population as compared to the BC₁-derived population, which might be due to a stronger selection by breeders for the two canola quality traits (zero erucic acid in seed oil and low glucosinolate in seed meal) in the F₂-derived population. Evaluation of the inbred populations in 10 field trials showed that the population derived from the cross involving var. italica gave the greatest yield, while the population derived from the cross with var. botrytis had the highest seed oil content; this population also gave high seed yield. In regard to the performance of the test hybrids,  population derived from the cross involving var. alboglabra gave the greatest mid-parent heterosis (MPH) (11.1 ± 2.2 S.E. %) while the population derived from the cross involving var. italica gave the lowest MPH (4.0 ± 2.2 S.E. %); however, individual test hybrid exhibiting upto 82.7% MPH was found in this population. Multivariate analysis showed that inbred lines or test hybrids with high seed yield and oil content, and earliness of flowering and maturity with longer grain-filling period can be obtained from this population.

A genome-wide association study using the above-mentioned inbred populations and 3,131 SNP markers detected 18 QTLs for three agronomic and seed quality traits; this included the QTLs located on chromosome C2, C3, C5 and C6 affecting days to flowering, QTLs on C1, C3, C5, C7 and C8 affecting seed oil content and QTLs on C1, C2, C3, C5 and C6 affecting seed glucosinolate content. Novel QTLs and alleles, which have not been reported previously, were also identified in this study, e.g. the C5 QTL affecting days to flowering; in this case, the alternative allele was derived from B. oleracea var. capitata cv. Bindsachsener and this allele improved the earliness flowering. Thus, the results from this study provided substantial evidence that the B. oleracea gene pool can be used to broaden the genetic base of B. napus canola for the improvement of inbred and hybrid cultivars of this crop as well as for identification of novel QTLs and alleles for different traits.