Borhan: Improving the Durability of Resistance to Blackleg in Brassica Napus Using the Novel LepR4 Gene
Date: April 2013
Term: n/a
Status: Completed
Researcher(s): Dr. Hossein Borhan, Agriculture and Agri-Food Canada, Saskatoon
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Developing genetically resistant canola varieties is the best and only effective method for controlling blackleg to date. Researchers at Agriculture and Agri-Food Canada have been able to locate the resistance gene LepR4 and develop DNA based markers in close proximity to this gene. The DNA markers allow plant breeders to rapidly move the LepR4 gene from the candidate lines identified in the research project to desired commercial canola cultivars. Incorporation of LepR4 into commercial cultivars will enhance the resistance of these lines against blackleg and help to protect Canadian growers against potential yield loss.
Blackleg is a serious disease of canola caused by the fungus Leptosphaeria maculans. To date the best and only effective method for controlling blackleg is by developing genetically resistant canola varieties. Researchers at Agriculture and Agri-Food Canada in Saskatoon have screened a diverse collection of canola varieties for resistance against Canadian isolates of blackleg pathogen.
Resistance gene LepR4 (Leptosphaeria Resistance 4) was identified in a previous study, which is effective against multiple isolates of the blackleg pathogen (Figure 1). The analysis also indicated that LepR4 provides the potential for at least two latent dominant resistance genes (LepR5 and LepR6) to control resistance to blackleg. The objective of this study was to provide canola breeders with canola donor lines containing the LepR4, LepR5 and LepR6 blackleg resistance genes, generate genetic map locations for each gene and identify molecular markers linked to each gene for marker-assisted selection in advanced canola breeding material.
Researchers used molecular markers linked to LepR4 to develop lines with resistance and evaluate the spectrum of LepR4 in these lines. Various crosses were made between Topas DH16516, a line susceptible to all blackleg isolates tested, and individuals from other lines with LepR4 resistance to develop candidate lines. Additional crosses were generated for mapping and further characterization of latent resistance genes. Fine mapping of LepR4 and mapping of potential latent R-genes LepR5 and LepR6 were continued.
Researchers confirmed LepR is a gene that confers resistance toward several isolates of L. maculans and has great potential in breeding for resistance to blackleg. They were also able to identify molecular markers in close proximity or with a close relationship to LepR4 locus, which will be highly valuable for incorporating the LepR4 genes into elite breeding lines. The fine mapping for potential latent R-genes (LepR5 & LepR6) was inconclusive despite using several different mapping populations.
From these results, researchers have been able to locate the LepR4 gene and develop DNA based markers in close proximity to this gene. The DNA markers allows plant breeders to rapidly move the LepR4 gene from the candidate lines identified in the research project to desired commercial canola cultivars. Incorporation of LepR4 into commercial cultivars will enhance the resistance of these lines against blackleg and help to protect Canadian growers against potential yield loss.
Figure 1: Cotyledons of the B. napus lines 16S-108 (with the LepR4 gene) and Topas DH16516 (without resistance genes) 14 days after inoculation with two isolates (07-37 and 89-13) of the blackleg pathogen Leptosphaeria maculnas. Cotyledons on the right are from the 16S-108 seedlings showing robust resistance to the blackleg disease after inoculation with two different isolates of the fungus. Cotyledons on the left show extensive lesion and complete collapse of the susceptible line Topas DH16516 after inoculation with the same isolates. One week old seedlings were inoculated by placing a drop of fungal spore suspension on the two pierced sites of each cotyledon.
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