Exploring disease resistance in the Brassica napus - Leptosphaeria maculans pathosystem
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Date
2016-07
Authors
Zhang, Xuehua
Journal Title
Journal ISSN
Volume Title
Publisher
Springer
Abstract
Blackleg disease, caused by the ascomycete fungal pathogen Leptosphaeria maculans, is a devastating disease of canola (Brassica napus) in Australia, Canada and Europe. The pathogen is considered a global invasive species and poses a threat to canola production in China, where only the weakly aggressive strain L. biglobosa is present. In Canada, breakdown of blackleg resistance has been shown. In order to develop a more effective disease management strategy, there is a need to elucidate host resistance and defense mechanisms underlying the B. napus-L. maculans pathosystem. This is the very first study to investigate major resistance genes (R genes) and adult plant resistance (APR) in Canadian canola germplasm. This study also analyzed the avirulence allele frequency in L. maculans populations in western Canada. R genes were detected in the majority of these B. napus germplasm, with the Rlm3 gene being predominant. The frequency of AvrLm3 allele in field fungal populations was extremely low. APR was identified in more than 50% of the germplasm. This indicated the breakdown of Rlm3 resistance, which could be due to the widespread use of this single resistance gene in Canadian B. napus germplasm and varieties. To address concerns of introducing L. maculans from Canada into China, this study further characterized R genes and APR to L. maculans in a collection of Chinese B. napus germplasm. R genes were detected in more than 40% of the germplasm tested, with Rlm3 and Rlm4 being predominant. A large portion of the Chinese germplasm showed high to moderate APR in field trials at three locations in MB, SK and AB in western Canada. This study highlighted the availability of fair to good resistance in the Chinese B. napus germplasm against blackleg disease and was the first study to investigate a large number of Chinese germplasm against Canadian fungal populations in different environments. RNA sequencing of resistant and susceptible host tissues and a streamlined bioinformatics pipeline identified unique genes and plant defense pathways specific to plant resistance in the B. napus-L. maculans LepR1-AvrLepR1 interaction. The sequencing data coupled with functional characterization of some unique genes, in depth histological analysis, and in situ gene activity analysis directly at the site of infection provide unprecedented spatial and temporal resolution of the plant defense response to L. maculans.
Description
Keywords
Blackleg, Brassica napus, Leptosphaeria maculans, resistance, RNA-Seq, R gene, adult plant resistance, transcriptome
Citation
Zhang, X., Peng, G., Kutcher, H.R. et al. Eur J Plant Pathol (2016) 145: 659. doi:10.1007/s10658-015-0819-0