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.

M.Sc. (Zoology) / Please refer to full text to view abstract

M.Sc. / Barley (Hordeum vulgare) production is a vital constituent of the South African economy. Many pathogens reside on barley, which lead to low quality and yield. One of the most prominent barley pathogens, Fusarium graminearum, is the causal agent of small grain scab. F. graminearum resistance to barley is regulated by multiple genes referred to as quantitative trait loci (QTL), which makes it difficult to breed for resistance in new cultivars. Each of these genes contributes to a specific defence area and collectively counteracts Fusarium infection and spread in the barley plant. The aim of this project was to isolate and identify induced genes after infection of three leave stage barley with F. graminearum. These genes were isolated through the use of Suppression subtractive hybridisation (SSH), cloned and then sequenced. From this data set three transcript derived fragments (TDFs) sharing homology to known genes were selected and their expression profiles were studied through Northern blot analysis. Three TDFs shared homology with known genes namely a putative protease inhibitor-related protein, a senescence associated gene, and a manganese superoxide dismutase (MnSOD). These TDFs were previously also recognised for their function in host pathogen interactions. The expression analysis done using Northern blots showed up-regulation of the three fragments after inoculation. These results indicated that all the TDFs studied may play a role in the defence reaction of barley infected with F. graminearum, where both senescence and proteinase inhibitors could limit infection as well as spread and MnSODs might be a protective enzyme against oxidative stress. The results of this study indicated that all of the identified TDFs had database matches to proteins identified during stress responses. Furthermore, the Northern blot results indicated that all the TDFs studied could play a role in the defence reaction of F. graminearum infected barley. These TDFs will form the basis of further studies into the interaction between barley and F. graminearum. The results form this study will add to our knowledge of the interaction between barley and a necrotrophic pathogen. This will aid in understanding how cereal pathogens deal with pathogen attack and will aid in development of new more tolerant barley cultivars.

M. Tech.

Citrus is grown as a commercial crop in several areas surrounding Grahamstown in the Eastern Cape Province of South Africa. Twelve miles South-west of Grahamstown is an orchard of about 6000 trees on the farm "Mosslands". This orchard attracted attention as the insect pests of citrus have been kept at a sub-economic level by natural biological control since 1949. This orchard is completely surrounded by indigenous bush and originally the object of this study was to see, in how far, the insect fauna of the indigenous bush was infuencing the biological control which had been achieved in the orchard. As citrus is a member of the family Rutaceae, four indigenous plants in this family, which occured in the indigenous bush, were chosen for a closer study of their associated insect fauna. This study continued for a year during which time a bewildering number of insects and their parasites were collected and it was realized that only an investigation of a very specific aspect of the problem could possibly yield meaningful results. As a starting point, therefore, Trioza erytreae (Del Guercio) (Homoptera: Psyllidae), the South African citrus psyllid, was singled out. This psyllid was found on citrus at "Mosslands" and was also found on all but one of the indigenous rutaceous plants. It was chosen for study because of its polyphagous habit and because very little is known of the biology of this economically important species in South Africa. Also very little work has been done on the Psyllidae generally. Intro., p. 1.

H. armigera larvae are a key stage for pest management in conmercial irrigated cotton crops in South Africa. Effective survey methods for detecting larval populations in the field require an understanding of the biology of the larvae, particularly their feeding habits. Their feeding is central to the development of pest threshold levels for the implementation of integrated control programmes. This applies to routine surveys for the larvae as well as to the damage they cause. Biological characteristics of the larvae are described with the emphasis on the identification of the larval instars, which were consistently five in number in both field and laboratory populations. The distribution of H. armigera larvae on cotton plants in the field was examined, but was found to more or less random; had there been a clear preference for any height zones or compass direction this would have been an obvious avenue for improving the survey methods currently in use. Details of field and laboratory investigations of the selection of feeding sites by the larvae are given. The study confirmed a clear preference by the larvae for cotton buds, flowers and bolls (in the thesis collectively called "fruiting forms"), over leaves. There were indications that the larvae selected flowers more readily than buds or bolls. This "preference", however, is shown to be of no practical value for refining survey methods. Damage levels to cotton due to B. armigera are discussed. Both direct losses and indirect losses due to the abortion of fruiting forms are considered. These criteria are inadequate since they do not take into account the ability of cotton plants to compensate for these losses. It is concluded that this compensation by cotton plants should be taken into account in further studies of the pest status of B. armigera.

Please read the abstract in the section 06resume of this document / Dissertation (MSc)--University of Pretoria, 2008. / Microbiology and Plant Pathology / unrestricted

False codling moth is a known pest of economic importance to many cultivated crops in South Africa and Africa south of the Sahara, and is particularly severe on citrus. If the fruit is infested just before harvest the chances of detecting signs of infestation are very low. As a result, the risk of packaging infested fruit and exporting them as healthy fruit is high. It is therefore a priority to develop a post-harvest technique for detection of False codling moth in citrus fruit at different levels of infestation in order to reduce phytosanitary risk. Compounds released and detected were indicative of infestation and were not insect produced but naturally produced fruit volatiles emitted at higher levels as a result of the insect within the fruit. Five major volatile compounds of interest were released by the infested oranges. These major volatile compounds include D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene, caryophyllene and naphthalene. Limonene was one of the most abundant volatile compounds released by the infested citrus fruit. Naphthalene, which is possibly produced due to larval feeding and development within the fruit maintained higher concentrations than controls throughout the infestation within the fruit. Naphthalene would be a good indicator of False codling moth infestation, however, not primarily for early infestation detection. A significantly higher concentration of D-limonene, 3,7-dimethyl-1,3,6-octatriene, (E)-4,8-dimethyl-1,3,7-nonatriene and naphthalene was detected using the SEP over the SPME technique. The application of an SPME procedure and the utilization of this method for detection of volatiles present in the headspace of intact infested fruit are evaluated and the possible volatile compounds diagnostic of Thaumatotibia leucotreta infestation of orange fruit and differences in volatile compound response in different orange varieties is discussed.

Cankering by Cytospora chrysosperma (Pers.) Fr. was investigated in a poplar nursery at Lulu Island, B. C. Cankers were observed to be more numerous in early winter than at other times and more numerous on Populus trichocarpa T & G than on the P.x canadensis hybrid cultivars P. ‘Robusta Bachieleri' and P. 'Regenerata'. The upper part of the shoot appeared to become cankered before the lower part. Experiments with cuttings of the three poplars showed that cankers developed from inoculations only when the bark moisture content was below a critical level. The hybrids were found to have a lower critical level than P. trichocarpa. Also, the incubation period was longer in the hybrids than in P. trichocarpa and longer in the lower part of the shoot than in the upper. Cankers were arrested when the cuttings were placed in water, the arresting time being shorter in the lower part of the shoot than in the upper part. Inoculated P. trichocarpa plants in the greenhouse became cankered when they were subjected to drought but the two hybrids required both drought and low relative humidity conditions for cankering to take place. The rate of moisture loss from cuttings exposed to a uniform relative humidity was found to be faster in P. trichocarpa than in the hybrids and faster from the upper part of the shoot than from the lower part. A basis for a superior water economy in the hybrids was suggested by their anatomical characteristics which included larger pith, wider vessels, greater sieve tube zone, more numerous bark fibres, thicker periderm and fewer lenticels than in P. trichocarpa. The lower shoot had a larger sieve tube zone, a thicker periderm and fewer lenticels than the upper part. In the nursery, the hybrids were found to have a significantly higher shoot moisture content during winter than P. trichocarpa and the lower part of the shoot had a higher moisture content than the upper part. The moisture content minima for all species occurred in late autumn. The results suggested that the greater resistance of the hybrids to Cytospora canker observed in the nursery was attributable to their greater water storage capacity and to the slower rate at which water was lost by evaporation during dormancy. The occurrence of the heaviest outbreaks of the disease in early winter could be attributed in part to the decrease in shoot moisture content in the late autumn. / Science, Faculty of / Botany, Department of / Graduate

A study was carried out to determine factors which influence the abundance of Adelges (Chermes) cooleyi Gill, on Douglas fir. This was done through the observation of populations in the field, supported by some laboratory work designed to show that certain influences are important. The work was done during the summer of 1960 in a young stand in Totem Park near Marine Drive and Agronomy Road on the U.B.C. campus, Vancouver. The following items were investigated: 1.) Inter tree differences, 2.) Intra tree variations, 3.) Population changes with time, 4.) Mortality of the insect. Abundance was affected by extrinsic influences on the trees, such as location and exposure and intrinsic factors such as time of bud opening and twig length. Within a tree the abundance of Adelges cooleyi was affected mostly by microclimatic factors, resulting in high abundance of the insect in the peripheral part of the lower crown. The average number of living insects decreased with time rectilinearly in generation 1 (Sexuparae and Progredientes) and logarithmically in generation 2 (Neosistens). A critical period during establishment of generation 2 caused the logarithmic changes. Mortality estimates by direct counts were subject to a large error because many of the dead insects fell off. / Forestry, Faculty of / Graduate