Overexpression of BnNAC19 in Brassica napus enhances resistance to Leptosphaeria maculans, the blackleg pathogen of canola
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Abstract Leptosphaeria maculans is a fungal pathogen that causes blackleg disease in canola ( Brassica napus ), resulting in significant yield and economic losses in Canada and many parts of the world. Plant NAC transcription factors play critical roles in plant development and response to biotic or abiotic stress. In this study, we identified and characterized a BnNAC19 gene from Brassica napus . The overexpression of BnNAC19 in transgenic canola plants contributed to the improvement of seedling resistance against L. maculans . The mycelial growth of a green fluorescent protein‐tagged strain of L. maculans and production of pycnidiospores were shown to be inhibited in the transgenic canola plants overexpressing BnNAC19 . In addition, the canola transgenic line overexpressing BnNAC19 showed increased disease resistance in the adult plant, which was determined by quantitative resistance. Both increased seedling and adult plant resistance in transgenic canola plants overexpressing BnNAC19 indicate that the BnNAC19 gene plays a positive role against L. maculans . The expression pattern of genes BnNAC19 upstream and downstream of BnNAC19 that participate in plant defence pathways were investigated to elucidate the B. napus resistance mechanisms to L. maculans infection, and hence to aid the long‐term blackleg disease‐resistant breeding programmes.Keywords:
Leptosphaeria maculans
Blackleg
WRKY protein domain
Blackleg
Leptosphaeria maculans
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Leptosphaeria maculans
Blackleg
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Blackleg, caused by Leptosphaeria maculans, is an economically important disease of canola (Brassica napus). Little is known about the current distribution of pathogenicity groups (PGs) of L. maculans in Canada and the United States. Four hundred and eighty-nine isolates of L. maculans or Leptosphaeria biglobosa from western Canada and North Dakota, United States, were placed in five PGs (PG-1 recognized as L. biglobosa since 2001, PG-2, PG-3, PG-4, and PGT) on the basis of a series of inoculations on canola cultivars ('Westar', 'Glacier', and 'Quinta'). Only PG-1 and PG-2 were observed in populations from a 1984 to 2001 collection. All five PGs were observed in populations collected between 2002 and 2004. New, more aggressive strains of L. maculans may pose a significant threat to the canola industry in Canada and the United States.
Leptosphaeria maculans
Blackleg
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Due to the large increase of canola production in Australia, current blackleg cultural control recommendations (extended rotation length and isolation distance from canola stubble) are not adhered to by farmers in many canola-producing regions. Canola crops are increasingly being sown in short rotation and, in many instances, adjacent to paddocks containing canola stubble. In this study, the level of disease in commercial canola crops was determined for different rotations and distances from canola stubble. There was a strong relationship between the presence of canola stubble from the previous year (6-month-old stubble) and distance to current canola crops, but no relationship between the presence of older (18–42 month old) stubble and distance to current canola crops. Blackleg severity was highest where canola crops had been sown adjacent to 6-month-old canola stubble, with the level of blackleg severity decreasing markedly in the first 100 m. Disease severity then generally declined up to 500 m. Plants 500–1000 m from 6-month-old stubble had similar levels of blackleg infection. Blackleg severity was similar between canola crops sown into 18-month-old canola stubble (short rotation) and crops sown into paddocks that had no history of canola for at least the previous 3 years (long rotation). Based on these findings, we recommend that canola crops should be sown at distances greater than 100 m and preferably 500 m from last season's canola stubble, rather than extending rotation length between crops.
Blackleg
Leptosphaeria maculans
Crop Rotation
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Leptosphaeria maculans
Blackleg
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Abstract Leptosphaeria maculans is a fungal pathogen that causes blackleg disease in canola ( Brassica napus ), resulting in significant yield and economic losses in Canada and many parts of the world. Plant NAC transcription factors play critical roles in plant development and response to biotic or abiotic stress. In this study, we identified and characterized a BnNAC19 gene from Brassica napus . The overexpression of BnNAC19 in transgenic canola plants contributed to the improvement of seedling resistance against L. maculans . The mycelial growth of a green fluorescent protein‐tagged strain of L. maculans and production of pycnidiospores were shown to be inhibited in the transgenic canola plants overexpressing BnNAC19 . In addition, the canola transgenic line overexpressing BnNAC19 showed increased disease resistance in the adult plant, which was determined by quantitative resistance. Both increased seedling and adult plant resistance in transgenic canola plants overexpressing BnNAC19 indicate that the BnNAC19 gene plays a positive role against L. maculans . The expression pattern of genes BnNAC19 upstream and downstream of BnNAC19 that participate in plant defence pathways were investigated to elucidate the B. napus resistance mechanisms to L. maculans infection, and hence to aid the long‐term blackleg disease‐resistant breeding programmes.
Leptosphaeria maculans
Blackleg
WRKY protein domain
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Abstract The survival and impact on canola of Leptosphaeria maculans, the causal agent of blackleg, might be reduced by agents that decompose canola stubble. Fifty-six fungal isolates from wood or canola were evaluated for their ability to overcome several biological and (or) physical constraints to their effectiveness in decomposing and (or) eliminating L. maculans from canola stubble. Relative to fungi from canola, wood decay fungi were more tolerant of reduced water potential but somewhat less tolerant of lower temperature. Wood decay fungi were no better than those isolated from canola at decomposing sterile canola stubble and less able than Coprinus spp. and Cyathus olla in colonizing and surviving in nonsterile stubble. None of the isolates were effective in eliminating L. maculans from stubble pieces or causing significant decomposition of nonsterile stubble either under laboratory conditions or in the field. These results suggest that considerable effort would be required to find isolates effective in managing blackleg disease through stubble decomposition. Wood decay fungi would seem to have little potential as biological control agents in this pathosystem because of their inability to colonize and decompose nonsterile canola stubble. Keywords: Leptosphaeria maculans blacklegcanoladecomposition
Leptosphaeria maculans
Blackleg
Pathosystem
Phoma
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A limited survey was conducted to determine the pathogenicity groupings (PG) of Leptosphaeria maculans associated with canola (Brassica napus var. oleifera) blackleg in south central Kentucky. In addition, multiyear ascospore discharge patterns were determined for infested canola stubble from seven fields. Strains PG3 and PG4 of L. maculans were most commonly associated with blackleg in Kentucky (18.4 and 79% of the isolates tested, respectively). One weakly virulent PG1 isolate (2.6%) and no PG2 isolates were found. L. maculans-infested canola stubble discharged ascospores within I week of harvest in 1990 and 1991. Early discharge patterns were not determined in 1989. Stubble collected each year released significant quantities of ascospores in the fall and winter months following crop harvest. However, few ascospores were released from infested stubble after the first year following crop production. The implications of these data in blackleg management are discussed.
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Blackleg
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Blackleg disease (phoma stem canker) caused by the fungus Leptosphaeria maculans is a major disease of canola (oilseed rape, Brassica napus ) worldwide. Canola plants in pots were exposed to blackleg‐infested stubble of canola with different complements of resistance genes and then assessed for disease. Plant mortality was reduced when plants were exposed to stubble from a cultivar with a different complement of resistance genes compared to stubble of a cultivar with the same resistance gene. These findings were consistent with 7 years of field surveys, which showed that changes in selection pressure as a result of extensive sowing of cultivars with major‐gene resistance, termed ‘sylvestris resistance’, dramatically influenced the frequency of virulent isolates in the population towards particular resistance genes, and therefore disease severity. All these data were supported by PCR‐genotyping surveys of fungal populations whereby the frequency of virulence alleles of avirulence genes AvrLm1 and AvrLm4 changed significantly depending on the resistance gene present in the cultivar from which the isolates were cultured. This is the first example of a study showing that sowing of canola cultivars with different complements of resistance genes in subsequent years, i.e. rotation of resistance genes, minimizes disease pressure by manipulating fungal populations. This approach provides a valuable disease management strategy for canola growers and is likely to be applicable to other plant diseases.
Blackleg
Leptosphaeria maculans
Canker
Phoma
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Blackleg, caused by Leptosphaeria maculans, is a major threat to canola production in Canada. With the exception of China, L. maculans is present in areas around the world where cruciferous crops are grown. The pathogen can cause trade barriers in international canola seed export due to its potential risk as a seed contaminant. The most recent example is China restricting canola seeds imported from Canada and Australia in 2009. Therefore, it is important to assess the level of Blackleg infection in Canadian canola seed lots and dockage (seeds and admixture). In this study, canola seed lots and dockage samples collected from Western Canada were tested for the presence of the aggressive L. maculans and the less aggressive L. biglobosa. Results showed that both L. maculans and L. biglobosa were present in seed lots and dockage samples, with L. biglobosa being predominant in infected seeds. Admixture separated from dockage had higher levels of L. maculans and L. biglobosa infection than samples from seed lots. Admixture appears to harbour higher levels of L. maculans infection compared to seeds and is more likely to be a major source of inoculum for the spread of the disease than infected seeds.
Leptosphaeria maculans
Blackleg
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