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Horsham, Australia

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. Source


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. Source


Sprague S.J.,CSIRO | Kirkegaard J.A.,CSIRO | Marcroft S.J.,Marcroft Grains Pathology | Graham J.M.,CSIRO
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. Source


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 Source


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. Source

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