M.Tech. / Mycotoxins are toxic substances naturally produced by moulds (fungi) that may contaminate agricultural commodities by growing on grain or feed. These moulds produce in a variety of dangerous mycotoxins, such as aflatoxin, fumonisin, deoxynivalenol (DON), ochratoxin, and zearalenone, and may induce acute or chronic effects (carcinogenic, mutagenic, tetragenic and oestrogenic) in humans and animals if ingested. Wheat is an important cereal grown in most provinces of South Africa and yet little is known with respect to incidence of its infection with fungi, contamination with mycotoxins or what carry over of these toxins is into human food. The purpose of this project is to investigate the incidence of fungi and mycotoxins in samples of wheat taken from specified areas in South Africa with a view to finding out if there is indeed a problem and, if so, what would be its impact on the industry and consumers. This pilot project would then form the basis for further studies in other geographical areas and how wheat-based foods for human consumption are affected. Mycotoxins have probably been present in food and feed since the beginning of human existence. Some of their effects have been known for hundreds of years. The technology to detect and chemically characterize them has only really developed in the last 40 years, particularly since 1980. Very small quantities of many of the important mycotoxins can now be detected and accurately measured in foods and feeds. In addition to those already known, many others are known to exist, but have not yet been chemically characterized. Scientists are now identifying toxic compounds in food faster than the information can be processed. However, to maintain perspective, it must be remembered that these substances have always been there, that humans have always been eating the food in which they occur and in the case of many substances, only the dose makes the poison. This study investigated the presence of toxigenic fungi and mycotoxins in wheat and wheat-based products, and also did a pilot study on a few heavily contaminated field wheat (HCFW) samples. Fusarium species dominated the mycological contamination at 40 to 65%, Aspergillus 45%, Penicillium 41% Mucor and Rhizopus were also detected. Among the Fusarium species isolated, six were identified as F graminearum, F. solani and F. vertillioides-like and F subglutinans. Phoma species were also isolated. Quantitative and qualitative analysis by, multi-mycotoxin screen method and VICAM method to analyze foods and feeds was used. Deoxynivalenol was the most prevalent at 45% incidence in samples with a mean concentration of 4.6ppm, aflatoxins in 12% of the samples with a mean concentration of 1.2ppb, ochratoxin in 16% of the samples with a mean of 1.5ppb, zearalenone in 18% of the samples with a mean of 0.1ppb. Attention was drawn to the potential presence of fumonisin in wheat, where fumonitest VICAM method was used, fumonisins were detected on few samples at very low levels of 1 to 2ppm in commercial wheat, and a high reading of 49ppm was recorded on one of the heavily contaminated field wheat (HCFW) samples. Confirmation of these results was carried out with the use of the liquid chromatography coupled with mass spectrum (LC/MS) and high-pressure liquid chromatography (HPLC) system. These results indicate an incidence of mycotoxin in these products, a recommendation of monitoring for prevention of moulds and mycotoxins is suggested. Since health concerns related to dietary exposure to mycotoxins depend on the levels of mycotoxins in the food as consumed, on the amount of food consumed and on the body weight and physiology state of the individual. Therefore, there is a likely possibility that in South Africa, some of the population is exposed to mycotoxins through consumption of wheat and its by-products.

A Thesis Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the Degree of Doctor of Philosophy / The Epidemiology, occurrences and effect of BMV (Brome Mosaic virus) wheat (triticum aestivum) in the summer rainfall area. (Abbreviation abstract) / AC 2018

Call number: LD2668 .T4 1952 H8 / Master of Science

Call number: LD2668 .T4 1986 C374 / Master of Science / Plant Pathology

Photocopy of typescript. / Digitized by Kansas Correctional Industries

ix, 223 leaves : ill., graphs, tables photos (part col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Pathology, 1979

Bibliography: leaves 184-209. This thesis describes the occurence of natural, biologically based suppression of Rhizoctonia barepatch in a direct drilled system at Avon, South Australia. The supressive characteristics are transferable, removed by biocidal treatments, and active against increasing doses of R. solani AG-8, Gaeumannomyces graminis var. tritici and Fusarium graminearum. Disease severity and the viable population of Rhizoctonia are reduced in suppressive soil but the causal agent is still present. The microbial populations in suppressive and non-suppressive soil appear to differ both in their functioning and composition. The control strategy is developed through manipulation of the existing soil biota with farming practices.

Tan spot of wheat is an economically significant disease caused by the fungal pathogen, Pyrenophora tritici-repentis. Certain races of the fungus secrete Ptr ToxA (ToxA), a 13.2 kDa proteinaceous host-selective toxin that is responsible and sufficient to cause disease in susceptible wheat varieties. Disease symptoms develop only when the ToxA gene in the fungus and a single gene in the wheat host are expressed. The understanding of this gene-for-gene interaction could be instrumental towards control of the disease and is also being developed as a model system for understanding host-pathogen interactions. Here, this effort is given a solid structural foundation through crystallographic analysis of the ToxA structure. The ToxA structure was solved at 1.65 Å resolution using the anomalous signal from inherently present sulfur atoms. The monomeric toxin adopts a β-sandwich fold of two anti-parallel β-sheets composed of four strands each. The mapping of existing mutation data onto the structure reveals that a sequence of Arg- Gly-Asp(RGD) and surrounding residues required for activity are present on a solvent-exposed loop thereby making them potential candidates for recognition events that are required for ToxA activity. Unexpectedly, after a simple circular permutation, the ToxA structure is topologically identical to the classic mammalian RGD containing fibronectin type III (FnIII) domain, and furthermore the RGD residues are topologically equivalent. These results support the hypothesis that ToxA, like FnIII, interacts with an integrin-like receptor on the host plant cell surface. There has been a renewed interest in the method of using the anomalous signal from sulfur atoms to solve protein structures. As a spin-off of the structure solution work, the data were systematically analyzed to study the effects of crystal decay, resolution and data redundancy on the ability to locate the sulfur positions and subsequent phasing of the protein. The analyses show that the choices made about data redundancy and resolution limits may be crucial for the structure determination and that anomalous correlation coefficients are helpful indicators in making these choices. / Graduation date: 2006

Cephalosporium stripe of wheat (Triticum aestivum), caused by the soilborne fungus Cephalosporium gramineum, results in significant yield reductions in dryland winter wheat crops of the U.S. Pacific Northwest. The development of resistant cultivars offers the best hope for disease control. Breeding for resistance is hampered by the long trial times inherent in screening adult plants, and by cultivar x environment interactions in field tests. The principal objective of this research was to develop and test a procedure for screening wheat seedlings in controlled environments for resistance to Cephalosporium stripe. Wheat seedlings were raised hydroponically in growth chambers, and the fungus was increased in large fermentation tanks. The seedlings were inoculated at about 12 days post-germination. Disease severity was assessed approximately seven days later using a chlorophyll meter to measure the symptoms of chlorosis and striping. In three trials, five soft white cultivars from the Pacific Northwest and four hard red cultivars from the Southern Great Plains with known levels of field resistance were tested with a Pacific Northwest fungal isolate. With one exception, chlorophyll readings ordered the cultivars appropriately, with moderately resistant cultivars ranking above susceptible cultivars. Three other moderately resistant cultivars from the Pacific Northwest also appeared in one or two trials, and were ranked properly by chlorophyll level. Chlorophyll levels of uninoculated plants were assayed to determine if differences in chlorophyll content were innate in the cultivars. The chlorophyll levels of uninoculated and inoculated seedling treatments were only significantly correlated when the cultivar Madsen, which ranks high both in resistance and in chlorophyll content, was included. In adult plants, flag-leaf chlorophyll level corresponded to intensity of Cephalosporium stripe symptoms where disease was present, and was independent of known field resistance in undiseased cultivars. The seedling screening technique was used to investigate pathogenic variability in C. gramineum. In two experiments, a total of eight cultivars from the Pacific Northwest and the Southern Great Plains were tested with three fungal isolates from each region. No evidence of virulence/vertical resistance was found. There was also no significant adaptation of isolates to greater virulence on cultivars from the same region. / Graduation date: 1998

Plant growth regulators and nitrogen fertilization have been associated with the increased incidence of fusarium head blight, a destructive disease of wheat (Triticum aestivum L.). In Canada, the major causal organism of this disease is Fusarium graminearum Schwabe, the conidial state of Gibberella zeae (Schw.) Petch. Most studies concerning the effect of plant growth regulators on fusarium head blight were conducted in fields with natural infection. The objective of this research was to evaluate the effect of growth regulators and nitrogen fertilizer on the incidence of fusarium head blight of wheat with artificial inoculations. / A survey conducted in a field trial testing the effect of the plant growth regulator Cerone on the yield components of several cultivars of spring wheat showed that Cerone treatments increased Fusarium infection only in cultivar Columbus. Further research was conducted using cultivar Max, a cultivar susceptible to fusarium head blight, which is widely grown in Quebec. In controlled-condition greenhouse trials, the growth regulators Cycocel and Cerone, as well as nitrogen fertilization did not influence the disease progress. In the 1991 field experiment, the highest incidence of seed infection was observed in Cycocel treatments when the macroconidia of F. graminearum were directly applied to the heads, but not significantly different from the non-treated control. None of the nitrogen levels affect the incidence of seed infection. In the 1992 field trial, the plots were treated with macroconidia of F. graminearum applied to the heads or with Fusarium-colonized corn applied to the rows. Both Cycocel and Cerone significantly increased the incidence of spikelet only in the colonized corn treatments. Cycocel also increased the incidence of seed infection, but only in colonized corn treatments. Cycocel also increased the incidence of seed infection in the non-inoculated treatments. Growth regulators had no effect on the disease when heads were inoculated directly with macroconidia.