Rahman: Investigation on the individual genes of Brassica carinata in canola (B. napus) for their resistance to different blackleg pathotypes

Date: October 2011
Term: 3 years
Status: Completed
Researcher(s): Dr. Habibur Rahman, R. Fredua-Agyeman, M. Rahman, Z. Navabi, Department of Agricultural, Food and Nutritional Science, University of Alberta
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: ACIDF, AFC, ACPC, MCGA

Project Summary

Blackleg is a serious disease of canola caused by the fungal pathogen Leptosphaeria maculans. A number of different sources of partial resistance genes (Rlm) to blackleg disease have been identified and characterized in several Brassica napus cultivars. Researchers at the University of Alberta initiated a new three-year project in 2007 to investigate the B. carinata derived resistance in doubled haploid (DH) lines to different blackleg pathotypes. The knowledge gained and the germplasm developed from this project can be applied in breeding of canola cultivars with resistance to multiple blackleg pathotypes.

Blackleg is a serious disease of canola caused by the fungal pathogen Leptosphaeria maculans. A number of different sources of partial resistance genes (Rlm) to blackleg disease have been identified and characterized in several Brassica napus cultivars including French, Japanese and Australian. The canola breeding program of the University of Alberta has been utilizing the resistance found in Australian canola (B. napus) cultivars, and have previously developed the canola cultivars Q2, Quantum, Hi-Q and others based on this resistance. Other breeders in Canada also extensively used this resistance for developing canola cultivars.

However, this resistance is ineffective against some known pathogenicity groups (PGs) or races of L. maculans and the evolution of other new races in the Canadian prairies is of increasing concern to canola growers. Researchers at the University of Alberta have been using an accession of Brassica carinata (Ethiopian mustard) from their canola breeding program, which carries resistance to multiple fungal diseases, to make a series of crosses with B. napus ‘Westar’. This was the first study that integrated molecular mapping with molecular cytogenetics to analyze the inheritance of B-genome chromosomes and traits in a B. napus background.

Researchers at the University of Alberta initiated a new three-year project in 2007 to investigate the B. carinata derived resistance in doubled haploid (DH) lines to different L. maculans pathotypes. They also wanted to study the inheritance of the B. carinata derived resistance in a high oil content canola background through crossing with a blackleg susceptible cultivar Polo to understand the effect of pyramiding the B. carinata resistance genes in canola B. napus to different blackleg pathotypes; and to initiate a new interspecific cross of B. napus x B. carinata for introgression of PG4 resistance from B. carinata into B. napus.

To carry out these studies, interspecific crosses were done between B. napus (blackleg susceptible) x B. carinata (blackleg resistant) for the introgression or transfer of blackleg disease resistance from B. carinata into canola B. napus. The researchers used molecular cytogenetic analysis, molecular markers and combinations or gene pyramiding to develop DH lines carrying resistance genes. Further investigation would be needed to understand these lines for adult plant resistance, as well as for introgression of this resistance into the B. napus genome.

In the second B. napus x B. carinata interspecific cross, the interspecific hybrids were recurrently backcrossed to the blackleg susceptible cultivar Westar, and the progenies were evaluated for resistance to a PG4 type blackleg isolate. Although the proportion of plants showing resistance to PG4 isolate decreased progressively with the increasing number of backcrossing, a few plants in the third backcross generation were still found to be resistant to this isolate at the cotyledon and adult stages. These resistant plants preferentially maintained few B-genome chromosomes over the backcross generations, which possibly carry resistance to the PG4 type isolate. Further molecular cytogenetic characterization of this population would be needed to confirm which chromosomes carry this resistance, as well as for introgression into B. napus.

The knowledge gained and the germplasm developed from this project can be applied in breeding of canola cultivars with resistance to multiple blackleg pathotypes.

Scientific Publications

Navabi, Z.K., I.A.P. Parkin, J.C. Pires, Z. Xiong, M.R. Thiagarajah, A.G. Good, and M.H. Rahman. 2010. Introgression of B-genome chromosomes in a doubled haploid population of Brassica napus x B. carinata. Genome 53: 619–629.

Navabi, Z.K., S.E. Strelkov, A.G. Good, M.R. Thiagarajah, and M.H. Rahman. 2010. Brassica B-genome resistance to stem rot (Sclerotinia sclerotiorum) in a doubled haploid population of Brassica napus x Brassica carinata. Can. J. Plant Pathol. 32: 237–246.

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