Kurt Lindbeck

Genome-wide Association Study Identifies New Loci for Resistance to Leptosphaeria maculans in Canola

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.

Biology and biocontrol of Sclerotinia sclerotiorum (Lib.) de Bary in oilseed Brassicas

Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic plant pathogen infecting over 500 host species including oilseed Brassicas. The fungus forms sclerotia which are the asexual resting structures that can survive in the soil for several years and infect host plants by producing ascospores or mycelium. Therefore, disease management is difficult due to the long term survivability of sclerotia. Biological control with antagonistic fungi, including Coniothyrium minitans and Trichoderma spp, has been reported, however, efficacy of these mycoparasites is not consistent in the field. In contrast, a number of bacterial species, such as Pseudomonas and Bacillus display potential antagonism against S. sclerotiorum. More recently, the sclerotia-inhabiting strain Bacillus cereus SC-1, demonstrated potential in reducing stem rot disease incidence of canola both in controlled and natural field conditions via antibiosis. Therefore, biocontrol agents based on bacteria could pave the way for sustainable management of S. sclerotiorum in oilseed cropping systems.

Molecular mapping and validation of Rlm1 gene for resistance to Leptosphaeria maculans in canola (Brassica napus L.)

Abstract. European winter canola (Brassica napus L.) cultivars harbour genes for durable resistance to the fungus Leptosphaeria maculans, which causes blackleg disease under Australian environmental conditions. Previous studies have shown that resistance in winter-type cultivars Maxol and Columbus is controlled by two genes, Rlm1 and Rlm3, which have been mapped using randomly amplified polymorphic DNA markers onto chromosome A7. We mapped a doubled-haploid population that consisted of 101 lines from a cross between Maxol*1 and Westar-10 using diversity arrays technology and simple sequence repeat (SSR)-based markers. Two SSR marker loci, Xol12-e03 and Xra2-a05b, flanked the Rlm1 locus at an interval of 6.7 cM, which corresponds to ∼3.2 Mb of the Brassica rapa genomic sequence; this region contains several genes encoding putative kinase and leucine-rich repeat-type disease-resistance proteins. SSR markers were further tested for their linkage with the Rlm1 locus in an independent population derived from Columbus*3/Westar-10. Our results showed that SSR markers linked to Rlm1 can be useful for monitoring Rlm1 gene introgression in breeding populations derived from Maxol and Columbus.

G2 Blackspot Manager model to guide field pea sowing for southern Australia in relation to ascochyta blight disease

G2 Blackspot Manager, the second generation (G2) of Blackspot Manager model, predicts disease severity and yield loss in addition to quantified release of seasonal ascospores in relation to ascochyta blight on field pea. The model predicts the disease severity with respect to the expected exposure of field pea crop to ascospores of D. pinodes, with yield loss subsequently related to the disease severity. Both the relationships were developed using published and unpublished data under southern Australian conditions. The model has been used as a decision support tool for developing a field pea sowing guide considering weather-based disease risk and abiotic risk. This paper presents the field pea sowing guide for South Australia, Victoria and Western Australia for the 2010 season and compares it with 2009. The guide is dynamic as the disease severity changes with seasonal weather conditions and is updated weekly starting around mid-April, being delivered principally via the web (http://www.agric.wa.gov.au/cropdisease). The paper also discusses other means of communicating the guide to the stakeholders of southern Australia.

Formation of Didymella lentis, the teleomorph of Ascochyta lentis, on lentil stubble in the field in Victoria and Western Australia

Ascospores of Didymella lentis were trapped from lentil stubble that was weathered under natural conditions in the field in Western Australia and Victoria; naturally occurring pseudothecia were present on the stubble. This is the first report of the teleomorph of Ascochyta lentis on lentil stubble from the field in Australia. The presence of the teleomorph has implications in the long-distance dispersal of A. lentis and on resistance breeding programs.