School of Botany - Research Publications
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ItemComparison of transcription of multiple genes at three developmental stages of the plant pathogen Sclerotinia sclerotiorum(BLACKWELL PUBLISHING, 2006-05)The ascomycete Sclerotinia sclerotiorum is a plant pathogen with a very broad host range. In order to identify and characterize genes involved in S. sclerotiorum infection of Brassica napus (canola), expressed sequence tags (ESTs) were examined from libraries prepared from three tissues: complex appressorium (infection cushions), mycelia grown on agar and lesions formed on leaves of B. napus. A high proportion of genes (68%) had not been previously reported for S. sclerotiorum in public gene or EST databases. The types of novel genes identified in the infection cushion library highlights the functional specificity of these structures and similarities to appressoria in other fungal pathogens. Quantitative real-time PCR was used to analyse tissue specificity and timing of transcription of genes with best matches to MAS3 (appressoria-associated protein from Magnaporthe grisea), cellobiohydrolase I, oxaloacetate acetylhydrolase, metallothionein, pisatin demethylase, and an unknown gene with orthologs in fungal pathogens but not in saprophytic fungi.
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ItemPopulation structure of Sclerotinia sclerotiorum in an Australian canola field at flowering and stem-infection stages of the disease cycle(NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS, 2006-11)Populations of the ascomycete pathogen Sclerotinia sclerotiorum sampled from a canola field were analysed using microsatellite markers. Fifty isolates were collected from ascospore-infested canola petals and, later in the season, another 55 isolates were obtained from stem lesions; these isolates were used to compare inoculum and disease-causing populations. Fifty-five unique haplotypes were identified, with gene diversity ranging from 0.40 to 0.71. Genotypic diversity was higher in the inoculum population than it had been in the previous year, but analysis of molecular variance (AMOVA) showed that less than 10% of the variation was attributable to differences between the 2 years. Genotypic disequilibrium measures were consistent with the occurrence of both clonal reproduction and out-crossing. There was no significant population subdivision between the ascospore and stem-lesion populations, as measured with fixation indices (R(ST) = 0.015, p = 0.90) and AMOVA, suggesting that there are no genetically defined subgroups of isolates more likely to proceed from petal colonization to cause stem infection. This might be because S. sclerotiorum possesses wide-ranging pathogenicity mechanisms that account for the lack of host specificity observed to date.
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ItemMicrosatellite markers reveal genetic differentiation among populations of Sclerotinia sclerotiorum from Australian canola fields(SPRINGER, 2004-12)Eight microsatellite markers were applied to 154 Sclerotinia sclerotiorum isolates from four Australian canola fields, to determine the extent of genetic variation and differentiation in populations of this pathogen. A total of 82 different haplotypes were identified and in each population many haplotypes were unique. Mycelial compatibility grouping, a phenotypic marker system controlled by multiple loci, was often associated with groups of identical or closely related microsatellite haplotypes. Genotypic diversity ranged from 36% to 80% of maximum in the four populations, and gene diversity ranged from 0.23 to 0.79. Genotypic disequilibrium analyses on each of the four populations suggested that both clonal and sexual reproduction contributed to population structure. Analyses based on genetic diversity and fixation indices demonstrated a moderate to high level of differentiation (R(ST)=0.16-0.33, F(ST)=0.18-0.23) between populations from New South Wales and those from Victoria. Despite this genetic diversity, most isolates did not vary in virulence on canola leaves.
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ItemParallels in fungal pathogenesis on plant and animal hosts(AMER SOC MICROBIOLOGY, 2006-12)