Alternaria tagetica is capable of producing phytotoxins in vitro. One toxin was identified as zinniol with: bioassays; thin-layer and gas chromatography; staining properties; ultraviolet and mass spectrometry, and nuclear magnetic resonance spectroscopy. The identity of the other toxin(s) has not been established. Symptoms similar to those caused by infection developed on detached marigold leaves treated with either of the toxins or synthetic zinniol. The toxins are not host selective. The distribution of zinniol among Alternaria species was studied. Thirty-one isolates of 10 pathogenic Alternaria spp. were tested for their ability to produce zinniol. Analyses were performed by gas-liquid and thin-layer chromatography. Of the seven pathogenic large-spored, long-beaked species tested A. carthami, A. macrospora, A. porri, A. solani, A. tagetica, and an unnamed isolate from Phaseolus vulgaris pods produced zinniol. A. brassicae, a non-pathogenic isolate of A. zinniae, and three pathogenic species lacking large-spores and long-beaks (A. alternata, A. citri, and A. raphani) did not produce zinniol. The quantity of zinniol produced varied greatly among species, among isolates of a single species, and between trials of the same isolate. All hosts of the Alternaria spp. tested were sensitive to zinniol at 50 to 200 micrograms/ml. Conservation of zinniol in pathogenic large-spored Alternaria spp. may be indicative of its importance in pathogenesis. Light affects the behavior of Alternaria tagetica in vitro and in vivo. In vitro zinniol production occurred only during active fungus growth in the light; in the dark zinniol production occurred primarily after growth stopped. In all filtrates, the quantity of zinniol rapidly declined once zinniol production ceased. Fungus growth was inhibited by both continuous and alternating light and sporulation occurred on one of three test media and only under alternating light. More lesions were produced on inoculated plants kept in dark humidity chambers than in illuminated humidity chambers. Low illuminance was more conducive to lesion development than high illuminance and more lesions developed on plants exposed to low illuminance for 48 hr prior to inoculation than on those exposed to high illuminance. The limitations of studies in which the effect of light has been overlooked are discussed.

Thesis (M. Sc.)--Carleton University, 1989. / Also available in electronic format on the Internet.

M.F. Dutton

M. Tech.

No description available.

D.Tech. (Biomedical Technology) / To determine the quality of human food commodities commonly consumed in Cameroon, various districts in the western highland (Bamenda and Kumbo) and tropical rain forest (Douala and Yaounde) regions were sampled. Two mycological investigations were conducted to evaluate the incidences of mycotoxigenic fungi (95 samples) and mycotoxins (82 samples). Serial dilution of ground samples was employed to isolate fungi, subculture on various culture media and fungal species were identified morphologically followed by molecular phylogenetic approach. In general, data obtained indicate samples from various geographical regions showed no consistent variation with regard to the type of fungal species. The mycobiota of food materials were characterized by a diversity of fungal species with the predominance of Aspergillus (125 isolates) followed by Penicillium (94 isolates) and Fusarium (52 isolates). The less predominant genera include Rhizopus (14 isolates) and the Alternaria (9 isolates). Aspergillus flavus and A. parasiticus occurred in 53 and 44% of the samples, respectively, with higher frequencies in maize than peanuts or beans and absent in rice, pumpkin seed and cassava products. Aspergillus fumigatus was detected in 20% of samples and A. niger in 18% of the samples. Aspergillus isolated less frequently included A. carbonarius A. awamori, A. oryzae and A. tamarii, A. pseudotamarii, A. ochraceus, A. ostianus, A. avenaceum, A. oryzae and A. variabile. Consistent results were observed for A. tamarii, A. pseudotamarii, A. ochraceus and A. ostianus with respect to substrate specificity. While A. tamarii, A. pseudotamarii and A. ochraceus were isolated only from peanuts, A. ostianus strains occurred only in bean samples. Penicillium contamination was dominated by P. polonicum and P. crustosum with incidence rates of 43 and 41%, respectively, with highest contamination levels registered in samples from Yaounde. Penicillium citrinum, P. purpurogenum, P. islandicum, P. aurantiogriseum, P. expansum were also inconsistently isolated from food samples. There was a relatively low incidence of Penicillium spp. in pumpkin seed and fermented cassava product samples.

No description available.

Ochratoxin A (OA), a nephrotoxin and potential carcinogen, has been found in many foods, including grapes and grape products. Limits of 2 μg/kg in wine and 10 μg/kg in dried vine fruit have been introduced by the European Union. This study presents information on the ecology of ochratoxin A production by black Aspergillus spp. in Australian vineyards, and the passage of the toxin throughout winemaking. Aspergillus niger and A. carbonarius were isolated from vineyard soils in 17 of 17, and four of 17 Australian viticultural regions, respectively. A. aculeatus was isolated infrequently. All thirty-two isolates of A. carbonarius and three of 100 isolates of A. niger produced OA. Of Australian A. niger isolates analysed for restriction fragment length polymorphisms within the internal transcribed spacer region of 5.8S ribosomal DNA, 61 of 113 isolates, including the three toxigenic isolates, were of type N pattern, and 52 were type T. A selection of these A. carbonarius and A. niger aggregate isolates, as well as imported isolates, were compared using enterobacterial repetitive intergenic consensus (ERIC)-PCR, amplified fragment length polymorphisms (AFLP) and microsatellite markers. ERIC and AFLP clearly differentiated A. niger from A.carbonarius. AFLP further divided A. niger into types N and T. Six polymorphic microsatellite markers, developed specifically for A. niger, also differentiated strains into N and T types. There was no clear relationship between genotypic distribution and ochratoxigenicity, substrate or geographic origin. The survival of A. carbonarius spores on filter membranes was examined at water activities (aw) 0.4-1.0, and at 1 °C, 15 °C, 25 °C and 37 °C. Survival generally increased at lower temperatures. The lowest water activity, 0.4, best supported the survival of spores, but 0.6- 0.9 aw was often deleterious. Complex interactions between temperature and water activity were observed. Viability of A. carbonarius spores on filter membranes decreased ca 10[superscript 5] fold upon exposure to sunlight, equivalent to 10 mWh of cumulative ultraviolet irradiation at 290-400 nm. Growth and toxin production were examined for five isolates of A. carbonarius and two of A. niger on solid medium simulating juice at early veraison, within the range 0.98-0.92 aw, and at 15 °C, 25 °C, 30 °C and 35 °C. Maximum growth for A. carbonarius and A. niger occurred at ca 0.965 aw / 30 °C and ca 0.98 aw / 35 °C, respectively. The optimum temperature for OA production was 15 °C and little was produced above 25 °C. The optimum aw for toxin production was 0.95 for A. niger and 0.95-0.98 for A. carbonarius. Toxin was produced in young colonies, however, levels were reduced as colonies aged. Black Aspergillus spp. were more commonly isolated from the surface than from the pulp of berries, and increased with berry maturity, or damage. A. niger was isolated more frequently than A. carbonarius and A. aculeatus. Populations of A. carbonarius inoculated onto bunches of Chardonnay and Shiraz decreased from pre-bunch closure to early veraison. Populations from veraison to harvest were variable, and ncreased in bunches with tight clustering and splitting. In a trial with Semillon bunches, omitting fungicide sprays after flowering did not increase the development of Aspergillus rot. Inoculation of bunches with A. carbonarius spore suspension did not necessarily result in Aspergillus bunch rot. In vitro trials suggested that the severity of rot was mediated primarily by the degree of berry damage, followed by the extent of spore coverage. No clear trends regarding cultivar susceptibility were observed. For Semillon bunches inoculated with A. carbonarius spores with and without berry puncture, increased susceptibility to rot and OA formation was associated with berry damage, in particular at greater than 12.3 °Brix (20 d before harvest). OA contamination of bunches was related to the number of mouldy berries per bunch, with shrivelled, severely mouldy berries the primary source of OA. Puncture-inoculation of white grapes (Chardonnay and Semillon) and red grapes (Shiraz) on the vine with A. carbonarius resulted in berries containing OA. Inoculated grapes displayed greater total soluble solids due to berry shrivelling, and greater titratable acidity due to production of citric acid by the fungus. Samples taken throughout vinification of these grapes were analysed for OA. Pressing resulted in the greatest reduction in OA (68-85% decrease in concentration, compared with that of crushed grapes). Additional reductions occurred at racking from grape and gross lees, and after storage. OA was removed by binding to marc, grape and gross lees. Pectolytic enzyme treatment of white must, bentonite juice fining, recovery of juice or wine from lees, and static or rotary style fermentation of red must, had no effect on OA contamination. Bentonite in white wine (containing 56 mg/L grape-derived proteins) and yeast hulls in red wine were effective fining agents for removing OA. Findings from these studies may contribute to the improvement of strategies to minimise OA in Australian wine and dried vine fruit. / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture and Wine, 2005.

Ochratoxin A (OA), a nephrotoxin and potential carcinogen, has been found in many foods, including grapes and grape products. Limits of 2 μg/kg in wine and 10 μg/kg in dried vine fruit have been introduced by the European Union. This study presents information on the ecology of ochratoxin A production by black Aspergillus spp. in Australian vineyards, and the passage of the toxin throughout winemaking. Aspergillus niger and A. carbonarius were isolated from vineyard soils in 17 of 17, and four of 17 Australian viticultural regions, respectively. A. aculeatus was isolated infrequently. All thirty-two isolates of A. carbonarius and three of 100 isolates of A. niger produced OA. Of Australian A. niger isolates analysed for restriction fragment length polymorphisms within the internal transcribed spacer region of 5.8S ribosomal DNA, 61 of 113 isolates, including the three toxigenic isolates, were of type N pattern, and 52 were type T. A selection of these A. carbonarius and A. niger aggregate isolates, as well as imported isolates, were compared using enterobacterial repetitive intergenic consensus (ERIC)-PCR, amplified fragment length polymorphisms (AFLP) and microsatellite markers. ERIC and AFLP clearly differentiated A. niger from A.carbonarius. AFLP further divided A. niger into types N and T. Six polymorphic microsatellite markers, developed specifically for A. niger, also differentiated strains into N and T types. There was no clear relationship between genotypic distribution and ochratoxigenicity, substrate or geographic origin. The survival of A. carbonarius spores on filter membranes was examined at water activities (aw) 0.4-1.0, and at 1 °C, 15 °C, 25 °C and 37 °C. Survival generally increased at lower temperatures. The lowest water activity, 0.4, best supported the survival of spores, but 0.6- 0.9 aw was often deleterious. Complex interactions between temperature and water activity were observed. Viability of A. carbonarius spores on filter membranes decreased ca 10[superscript 5] fold upon exposure to sunlight, equivalent to 10 mWh of cumulative ultraviolet irradiation at 290-400 nm. Growth and toxin production were examined for five isolates of A. carbonarius and two of A. niger on solid medium simulating juice at early veraison, within the range 0.98-0.92 aw, and at 15 °C, 25 °C, 30 °C and 35 °C. Maximum growth for A. carbonarius and A. niger occurred at ca 0.965 aw / 30 °C and ca 0.98 aw / 35 °C, respectively. The optimum temperature for OA production was 15 °C and little was produced above 25 °C. The optimum aw for toxin production was 0.95 for A. niger and 0.95-0.98 for A. carbonarius. Toxin was produced in young colonies, however, levels were reduced as colonies aged. Black Aspergillus spp. were more commonly isolated from the surface than from the pulp of berries, and increased with berry maturity, or damage. A. niger was isolated more frequently than A. carbonarius and A. aculeatus. Populations of A. carbonarius inoculated onto bunches of Chardonnay and Shiraz decreased from pre-bunch closure to early veraison. Populations from veraison to harvest were variable, and ncreased in bunches with tight clustering and splitting. In a trial with Semillon bunches, omitting fungicide sprays after flowering did not increase the development of Aspergillus rot. Inoculation of bunches with A. carbonarius spore suspension did not necessarily result in Aspergillus bunch rot. In vitro trials suggested that the severity of rot was mediated primarily by the degree of berry damage, followed by the extent of spore coverage. No clear trends regarding cultivar susceptibility were observed. For Semillon bunches inoculated with A. carbonarius spores with and without berry puncture, increased susceptibility to rot and OA formation was associated with berry damage, in particular at greater than 12.3 °Brix (20 d before harvest). OA contamination of bunches was related to the number of mouldy berries per bunch, with shrivelled, severely mouldy berries the primary source of OA. Puncture-inoculation of white grapes (Chardonnay and Semillon) and red grapes (Shiraz) on the vine with A. carbonarius resulted in berries containing OA. Inoculated grapes displayed greater total soluble solids due to berry shrivelling, and greater titratable acidity due to production of citric acid by the fungus. Samples taken throughout vinification of these grapes were analysed for OA. Pressing resulted in the greatest reduction in OA (68-85% decrease in concentration, compared with that of crushed grapes). Additional reductions occurred at racking from grape and gross lees, and after storage. OA was removed by binding to marc, grape and gross lees. Pectolytic enzyme treatment of white must, bentonite juice fining, recovery of juice or wine from lees, and static or rotary style fermentation of red must, had no effect on OA contamination. Bentonite in white wine (containing 56 mg/L grape-derived proteins) and yeast hulls in red wine were effective fining agents for removing OA. Findings from these studies may contribute to the improvement of strategies to minimise OA in Australian wine and dried vine fruit. / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture and Wine, 2005.

Submitted in part fulfilment of the requirements for the Degree of Master of Technology: Biotechnology, Durban Institute of Technology, 2004. / Various methods have been developed for the analysis of Fusarium and its toxins. Advances in molecular biology can lead to efficient characterization of this group of fungi. This study was undertaken to examine random amplified polymorphic DNA, volatile compound production and hydrolytic enzyme production by 19 Fusarial isolates. These techniques were employed to assess their abilities in differentiating Fusarium species and F. verticillioides strains and extending the analysis to discriminate toxin producing capabilities amongst these fungi