Van de Wouw A.P.,University of Melbourne |
Idnurm A.,University of Melbourne |
Davidson J.A.,South Australian Research And Development Institute |
Sprague S.J.,CSIRO |
And 3 more authors.
Australasian Plant Pathology | Year: 2016
Fungal diseases are the major constraint on canola (Brassica napus) production in Australia and worldwide. Blackleg (caused by Leptosphaeria maculans) and Sclerotinia stem rot (Sclerotinia sclerotiorum) are the predominant diseases limiting production but, with increased intensification of production, other diseases previously considered of minor importance and sporadic may be increasing in prevalence. We report on the incidence and severity of four ‘minor’ diseases of canola in Australia: white leaf spot (caused by Pseudocercosporella capsellae), downy mildew (Peronospora parasitica), Alternaria leaf and pod spot (Alternaria brassicae) and powdery mildew (Erysiphe cruciferarum). Diseases were monitored at more than 30 sites across Australia from 2013 to 2015. Regions were identified in which specific diseases are a consistent problem, such as white leaf spot in Hamilton in Victoria. In these regions, control strategies to minimise disease may be required. Varietal differences were observed for some diseases suggesting that resistance to these pathogens is already present in Australian advanced breeding material. Lastly, fungicide applications were shown to control some diseases such as white leaf spot. © 2016, Australasian Plant Pathology Society Inc.
Raman R.,Charles Sturt University |
Taylor B.,Charles Sturt University |
Marcroft S.,Marcroft Grains Pathology |
Stiller J.,University of Queensland |
And 10 more authors.
Theoretical and Applied Genetics | Year: 2012
Blackleg, caused by Leptosphaeria maculans, is one of the most important diseases of oilseed and vegetable crucifiers worldwide. The present study describes (1) the construction of a genetic linkage map, comprising 255 markers, based upon simple sequence repeats (SSR), sequence-related amplified polymorphism, sequence tagged sites, and EST-SSRs and (2) the localization of qualitative (race-specific) and quantitative (race non-specific) trait loci controlling blackleg resistance in a doubled-haploid population derived from the Australian canola (Brassica napus L.) cultivars Skipton and Ag-Spectrum using the whole-genome average interval mapping approach. Marker regression analyses revealed that at least 14 genomic regions with LOD ≥ 2. 0 were associated with qualitative and quantitative blackleg resistance, explaining 4. 6-88. 9 % of genotypic variation. A major qualitative locus, designated RlmSkipton (Rlm4), was mapped on chromosome A7, within 0. 8 cM of the SSR marker Xbrms075. Alignment of the molecular markers underlying this QTL region with the genome sequence data of B. rapa L. suggests that RlmSkipton is located approximately 80 kb from the Xbrms075 locus. Molecular marker-RlmSkipton linkage was further validated in an F 2 population from Skipton/Ag-Spectrum. Our results show that SSR markers linked to consistent genomic regions are suitable for enrichment of favourable alleles for blackleg resistance in canola breeding programs. © 2012 Springer-Verlag.
Raman H.,Charles Sturt University |
Raman R.,Charles Sturt University |
Coombes N.,Charles Sturt University |
Song J.,University of Canberra |
And 9 more authors.
Frontiers in Plant Science | Year: 2016
Key message “We identified both quantitative and quantitative resistance loci to Leptosphaeria maculans, a fungal pathogen, causing blackleg disease in canola. Several genome-wide significant associations were detected at known and new loci for blackleg resistance. We further validated statistically significant associations in four genetic mapping populations, demonstrating that GWAS marker loci are indeed associated with resistance to L. maculans. One of the novel loci identified for the first time, Rlm12, conveys adult plant resistance in canola.” Blackleg, caused by Leptosphaeria maculans, is a significant disease which affects the sustainable production of canola (Brassica napus). This study reports a genome-wide association study based on 18,804 polymorphic SNPs to identify loci associated with qualitative and quantitative resistance to L. maculans. Genomic regions delimited with 694 significant SNP markers, that are associated with resistance evaluated using 12 single spore isolates and pathotypes from four canola stubble were identified. Several significant associations were detected at known disease resistance loci including in the vicinity of recently cloned Rlm2/LepR3 genes, and at new loci on chromosomes A01/C01, A02/C02, A03/C03, A05/C05, A06, A08, and A09. In addition, we validated statistically significant associations on A01, A07, and A10 in four genetic mapping populations, demonstrating that GWAS marker loci are indeed associated with resistance to L. maculans. One of the novel loci identified for the first time, Rlm12, conveys adult plant resistance and mapped within 13.2 kb from Arabidopsis R gene of TIR-NBS class. We showed that resistance loci are located in the vicinity of R genes of Arabidopsis thaliana and Brassica napus on the sequenced genome of B. napus cv. Darmor-bzh. Significantly associated SNP markers provide a valuable tool to enrich germplasm for favorable alleles in order to improve the level of resistance to L. maculans in canola. © 2016 Raman, Raman, Coombes, Song, Diffey, Kilian, Lindbeck, Barbulescu, Batley, Edwards, Salisbury and Marcroft.
PubMed | Jobs, Marcroft Grains Pathology, University of Wollongong, University of Western Australia and 3 more.
Type: | Journal: Frontiers in plant science | Year: 2016
van de Wouw A.P.,University of Melbourne |
Elliott V.L.,Marcroft Grains Pathology |
Ware A.,South Australian Research And Development Institute |
Lindbeck K.,Australian Department of Primary Industries and Fisheries |
And 2 more authors.
European Journal of Plant Pathology | Year: 2015
Blackleg disease caused by the pathogen Leptosphaeria maculans is the most devastating disease of canola (Brassica napus, oilseed rape). This disease occurs in all canola-growing regions of the world except China. It has been suggested that L. maculans contaminated seed and admixture (associated plant debris) could lead to a blackleg epidemic in China and as a consequence, restrictions on importations into China were placed on canola seed from Australia and Canada in 2009. We show that canola pods infected by L. maculans can lead to seed contamination, and resultant seedling infection, which then leads to cankering in adult plants. The fungus can sexually reproduce over summer on stubble derived from these plants. Airborne sexual spores are then released in the following year– thus completing the life cycle of the fungus from a contaminated seed and providing a potential source for an epidemic, particularly in countries such as China where canola cultivars do not have high levels of resistance to L. maculans. Furthermore, sexual fruiting bodies can also be produced on admixture. The presence of blackleg lesions on canola pods correlated with seed contamination by the blackleg fungus. Viability of L. maculans is reduced on contaminated seed over a twelve month period. Surveying blackleg disease in field trials in Australia showed that the presence and degree of stem cankers did not correlate with the level of pod infection. This suggests that pod lesions are likely to arise as a result of new infection events, rather than the pathogen moving from pre-existing infections (stem cankers) onto the pods. Furthermore, pod infections are likely to be a result of seasonal conditions rather than specific to regions where canola is cropped at a high intensity. © 2015 Koninklijke Nederlandse Planteziektenkundige Vereniging
Van De Wouw A.P.,University of Melbourne |
Marcroft S.J.,Marcroft Grains Pathology |
Howlett B.J.,University of Melbourne
Crop and Pasture Science | Year: 2016
Blackleg disease caused by the fungus Leptosphaeria maculans is the most important disease of canola worldwide. The impact of this disease on the development of the Australian canola industry, particularly over the last 20 years, is discussed. Deployment of a range of disease control measures has resulted in a thriving canola industry with production now approaching 4million tonnes annually. Discoveries about disease mechanisms and key plant and fungal genes are described. Analysis of the L. maculans genome sequence has enabled an understanding of how fungal populations can evolve rapidly to overcome disease resistance bred into canola cultivars. © CSIRO 2016.
Sprague S.J.,CSIRO |
Kirkegaard J.A.,CSIRO |
Marcroft S.J.,Marcroft Grains Pathology |
Annals of Applied Biology | Year: 2010
Canola (Brassica napus) crops for grazing and grain (dual-purpose) production provide an economic break-crop alternative for dual-purpose cereals in Australian mixed farming systems. Infection by Leptosphaeria maculans is the most prevalent disease in Australian canola crops with airborne inoculum released throughout the autumn and winter when crops are grazed. Glasshouse and field experiments were conducted to investigate the effect of mechanical defoliation (simulated grazing) on disease severity at plant maturity. In glasshouse experiments, stem canker severity increased from 4% to 24% in severely defoliated plants, but light defoliation had no effect compared with undefoliated control plants. Disease severity was increased with defoliation in all field experiments. Defoliation increased crown canker severity from 22.6% to 39.3% at Wagga Wagga and from 3.0% to 7.1% at Canberra and lodging from 9.6% to 11.9% at Naracoorte in the same set of cultivars assessed at each site. The increase in disease severity with defoliation was less in canola lines with moderate to high levels of stem canker resistance. Plants defoliated before stem elongation tended to develop less disease than those defoliated during the reproductive phase of plant growth. These findings suggest that the impact of grazing on L. maculans infection of canola crops can be minimised by sowing cultivars with a high level of stem canker resistance and grazing during the vegetative stage of plant growth prior to stem elongation. Further research is required to determine whether these management strategies are applicable in canola crops defoliated by grazing animals. © 2010 Association of Applied Biologists.
PubMed | Marcroft Grains Pathology and University of Melbourne
Type: Journal Article | Journal: Mycologia | Year: 2015
The propensity of a fungal pathogen to evolve virulence depends on features of its biology (e.g. mode of reproduction) and of its genome (e.g. amount of repetitive DNA). Populations of Leptosphaeria maculans, a pathogen of Brassica napus (canola), can evolve and overcome disease resistance bred into canola within three years of commercial release of a cultivar. Avirulence effector genes are key fungal genes that are complementary to resistance genes. In L. maculans these genes are embedded within inactivated transposable elements in genomic regions where they are readily mutated or deleted. The risk of resistance breakdown in the field can be minimised by monitoring disease severity of canola cultivars and virulence of fungal populations using high throughput molecular assays and by sowing canola cultivars with different resistance genes in subsequent years. This strategy has been exploited to avert yield losses due to blackleg disease in Australia.