-
[show abstract]
[hide abstract]
ABSTRACT: Leptosphaeria maculans, the causal agent of blackleg of canola, produces polygalacturonases during infection. Stem extracts of spring and winter canola cultivars contained a water-soluble inhibitor of the polygalacturonase activity of L. maculans. The polygalacturonase inhibitor material had different characteristics dependent upon the cultivar. Some canola cultivars had a polygalacturonase inhibitory compound(s) which was heat liable, low molecular weight and required divalent cations, and other cultivars had a heat stable, low molecular weight compound(s). The cultivar Maluka had a unique polygalacturonase inhibitory compound(s) that was heat labile, low molecular weight and did not need divalent cations. The level of the polygalacturonase inhibitory activity in the stem extracts was significantly related to the resistance of the cultivars to L. maculans as measured by the rate of lesion elongation, but was less related to the rate of stem girdling. The significant correlation between levels of polygalacturonase inhibitor activity and stem resistance in canola cultivars indicates that polygalacturonase inhibitors may be involved in the resistance of stems to blackleg. The two quantitative measures of stem resistance, rate of lesion elongation and rate of stem girdling, were significantly correlated to cotyledon resistance and to each other.
Journal of Phytopathology 04/2008; 145(5‐6):217 - 223. · 0.79 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: ABSTRACT Naturally established lowbush blueberry clones in four fields were evaluated for the incidence of leaf and flower blight, proportion of mummy berries, and yield reductions caused by Monilinia vacciniicorymbosi. The relationship between the phenology of flower and leaf bud development and susceptibility also was examined. Three fields were examined over one crop year and one field was studied in two subsequent crop years. The incidence of stems with blight was correlated to incidence of leaf blight in all fields and to incidence of flower blight in one field. Incidence of leaf and flower blight and the proportion of mummy berries produced were not correlated. Lowbush blueberry clones with higher incidence levels of leaf blight had reduced fruit set and lower berry weights. For healthy stems, leaf-to-fruit ratios had no effect on berry weight in most fields. In contrast, blighted stems with higher leaf-to-fruit ratios had higher berry weights in three fields. Stems with slowerdeveloping leaf and flower buds had less leaf and flower blight, respectively, than stems with faster bud development. Some blueberry clones may avoid infection by delaying production of susceptible tissue until after ascospore release by M. vaccinii-corymbosi.
Phytopathology 11/2005; 95(10):1174-82. · 2.80 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A novel assay is described for the identification and isolation of compounds that inhibit the transcription of genes involved in mycotoxin biosynthesis. The thin-layer chromatography-based assay was used to screen plant extracts for compounds that would inhibit the expression of the beta-glucuronidase reporter gene under the control of an aflatoxin biosynthesis gene promoter in Aspergillus parasiticus. The assay was used to track purification of an inhibitory compound, cp2, from extracts of black pepper (Piper nigrum). Cp2 did not inhibit mycelial growth or the expression of the beta-tubulin gene but did inhibit aflatoxin biosynthesis at the transcriptional level. Applications of cp2 to the control of mycotoxins are discussed.
Journal of Agricultural and Food Chemistry 11/2000; 48(10):4656-60. · 2.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The production of toxic ergopeptine alkaloids by the fungi Claviceps purpurea and Neotyphodium coenophialum involves the activity of one or more nonribosomal peptide synthetases. Claviceps purpurea and N. coenophialum each have several different peptide synthetase genes, fragments of which have been cloned previously. An additional Claviceps purpurea peptide synthetase gene was cloned by hydridization with one of the N. coenophialum peptide synthetase gene fragments. We detected the presence of mRNA from the peptide synthetase genes in cultures of different ages grown under conditions favorable or unfavorable for ergopeptine production. All four peptide synthetase genes from Claviceps purpurea were transcribed under at least some of the experimental conditions. Transcripts from three of the four genes were detected under conditions consistent with their potential involvement in ergopeptine biosynthesis. All three peptide synthetase genes previously identified in N. coenophialum were transcribed during symbiotic growth of this fungus with tall fescue, as well as ergopeptine-producing cultures. The data show that all of the peptide synthetase genes are transcribed, that one of the peptide synthetase genes is dissociated from ergopeptine biosynthesis, and, as a result, prioritize the remaining genes for functional analyses by transformation-mediated gene disruption.
Canadian Journal of Microbiology 01/1998; 44(1):80-6. · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The ascomycete fungus Cochliobolus carbonum race 1 is pathogenic on certain genotypes of maize due to the production of HC-toxin, a host-specific cyclic peptide. HC-toxin production is controlled, at least in part, by a duplicated 22-kb region of DNA that is found only in toxin-producing isolates of the fungus. This 22-kb region of DNA is flanked by a repetitive element. We have sequenced the element and found an interrupted reading frame that would encode a product similar to transposases from the fungal transposons Fot1 of Fusarium oxysporum and Pot2 of Magnaporthe grisea. The individual element cloned from C. carbonum is likely to function neither in cis nor trans, as it had a nonsense mutation in frame and several substitutions in its terminal inverted repeats. However, similar elements in the C. carbonum genome may be active, as the putative transposase-encoding region hybridized to mRNA of the size predicted by the reading frame. The element was found in varying copy number in the genomes of all Cochliobolus spp. examined, giving a distinct fingerprint in each species and race tested. The sequence similarity of the C. carbonum repetitive element to other fungal transposons, along with its presence in multiple copies per genome, strongly suggest that the C. carbonum repetitive element is a member of the Fot1 family of fungal transposons.
Gene 11/1996; 176(1-2):103-9. · 2.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Canadian isolates of Leptosphaeria maculans, the causal agent of blackleg of crucifers, were examined for genetic relatedness by the random amplified polymorphic DNA assay. DNA polymorphisms amplified with random decamer primers were used to distinguish three groups of isolates. Group 1 contained all isolates of the virulent pathotype, group 2 contained isolates of the avirulent pathotype from western Canada, and group 3 contained avirulent pathotype isolates from Ontario. These results agreed with other reports which showed many genetic differences between pathotypes and were consistent with the hypothesis that the virulent pathotype was recently introduced into Canada and has diverged relatively little. In contrast, the avirulent pathotype has probably been present in Canada for a longer time and has diverged with geographic isolation. In addition to establishing genetic relationships, DNA fingerprints generated by the random amplified polymorphic DNA assay have potential applications in pathotype identification and blackleg disease management.
Applied and Environmental Microbiology 10/1991; 57(9):2482-6. · 3.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In order to develop a pathotype-specific assay, the internal transcribed spacer region 1 (ITS 1) of ribosomal RNA genes of highly and weakly virulent isolates of Leptosphaeria maculans were sequenced using primers from the flanking 17S and 5·8S ribosomal DNA (rDNA). The sequenced ITS 1 region had approximately 67% similarity among highly and weakly virulent isolates, and 37–46% similarity between L. maculans and other species of fungi. From the ITS 1 sequences, two pairs of oligonucleotide primers were synthesized which specifically amplified DNA from either the highly or weakly virulent pathotype of L. maculans using the polymerase chain reaction (PCR). Primer pair HV17S/5·8S was based on sequences from the highly virulent isolates, Leroy and LM26, and only amplified highly virulent isolates. Primer pair WV17S/5·8S was based on sequences from the weakly virulent isolate, Unity, and only amplified weakly virulent isolates. This PCR-based assay utilizing pathotype-specific primers was employed to detect an isolate of the highly virulent pathotype of L. maculans in infected plant tissue and shows promise as a diagnostic tool.
Physiological and Molecular Plant Pathology.
