The work presented here represents research done on mycotoxins and plant toxins by the author and his postgraduate students over a period from 1964 to date. The first phase, which ends at 1980, mainly addresses the biosynthesis of the aflatoxins. The involvement of anthraquinone derivatives in this process was investigated and the role of versicolorin A and its derivatives was partially elucidated. Novel active enzymes systems were derived from protoplasts and used in these studies. The period lasting from 1980 to 1992 concentrates on the occurrence of mycotoxins in agricultural commodities and effects on animals and their systems. Over 7000 samples were analysed using a multimycotoxin analytical method and a fungal screen. The most common mycotoxin found was aflatoxin B₁ and prevalent fungus was Fusarium moniliforme. Later work is indicating that fumonisin B₁ is the most commonly occurring mycotoxin. As this was only discovered in 1988, its presence was only looked from 1995 onwards. It was also found that rumen fluid could metabolise trichothecenes. During this period (1980-1992) further work on aflatoxin metabolism was done and a novel dehydrogenase involved in aflatoxin B₁ was isolated and characterised. An Elisa assay was developed for atractyloside, a toxin found in a plant (Callilepis laureola) used in tradition medicine. The site of atractyloside storage was found to be in the plant vacuole. The final period covers 1992 to the present, where the occurrence and effects of mycotoxins in human disease were studied. The major and most important finding is that fumonisin B₁ is present in the blood and tissues of many of the Black population examined in Kwazulu Natal. This includes, oesophageal cancer patients, eclamptic patients, school children and members of the rural population. A similar circumstance also appertains for the presence of aflatoxin B₁. It seems likely from these results that chronic mycotoxicoses are a common occurrence, particularly in the Black rural population and are not the sporadic rare event that is found in the first world countries. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1999.

Poisonous plants are one of the most important causes of economic losses in the livestock industry throughout the world, especially in those areas where rangeland and pasture grazing are practiced. In the livestock industry in South Africa, total annual costs of plant and fungal poisoning (mycotoxicosis) are conservatively estimated to be R104 506 077, 8% of which is due to D. cymosum poisoning. There is no antidote for D. cymosum poisoning of livestock and wide scale eradication by conventional control methods are labour intensive, expensive and often impractical. In South Africa, the communal or emerging farming sectors are the most affected. This is mainly due to the high costs associated with control measures such as fencing, supplementary feeding and veterinary expenses, and / or lack of grazing management with livestock numbers exceeding the biological carrying capacity of the rangeland due to lack of grazing lands. Proper rangeland management is the surest and most economical means of reducing plant poisoning of livestock. Focused research on the ecology of these poisonous plants in rangeland communities to improve rangeland management would assist in the development of these strategies. This study investigated D. cymosum infested savanna communities, focusing on understanding how negative (inter- and intraspecific competition) interactions influence community structure, dynamics and productivity and how plants in D. cymosum communities avoid these negative interactions by investigating their seasonal phenological patterns. Dichapetalum cymosum coexists with trees, such as Burkea africana, Ochna pulchra and Terminalia serecia, as well as shrubs species, such as Pygmaeothamnus zeyheri and Perinari capensis, in well drained, nutrient poor soils. Some plant ecologists contend that in an environment where water is limited, competition is inevitable amongst plants occupying the same above-ground stratum and the same soil horizon. Others contend that plants avoid competition with each other by sharing resources spatially and temporarily. Field experiments were conducted to investigate how the above species interact and coexist with each other in two South African savanna communities. Fourteen (100 m x 100 m) D. cymosum infested sites were identified in each community. Disperal analysis using nearest neighbour distance was used to investigate competition among species, and above ground flowering phenology along niche axes to determine temporal and spatial sharing of resources. The dispersal analysis revealed aggregated populations among species when intraspecific and combined (all individuals independent of species) analyses were conducted. However, in all instances, aggregation among species was not significant. No interspecific competition was observed among species when correlation analysis was performed between nearest neighbour distance and combined canopy cover of the nearest neighbour pair. Intraspecific competition was, however, observed for tree species T. sericea (n = 128; r = 0.3952; P < 0.0001) and B. africana (n = 166; r = 0.49926; P <0.0001) and a shrub species, D. cymosum (n = 391; r = 0.39788; P <0.0001). Segregation was found between O. pulchra and both B. africana (S = 0.999, χ² = 102.7588, P <0.0001) and T. sericea (S = 0.999, χ² = 57.8571, P <0.0001). Shrub species were also segregated, all with interspecific nearest neighbour pairs occurring less often than expected. The vegetative phenology of all experimental plant species followed the rainfall gradient. Differences in reproductive phenologies were observed between O. pulchra and both B. africana and T. sericea. Dichapetalum cymosum also differed from P. capensis and P. zeyheri in their reproductive phenologies. The differences in the reproductive strategies of at least one of the species in each growth form account for the observed spatial distribution amongst species in these communities. The observed growth patterns shown by the vegetative phenologies, however, suggest that lengthy retention of nutrients is a strategy to avoid competition for nutrient uptake with other species in these communities. Segregation between species and positive correlation iii between nearest neighbour distance and combined canopy cover of the nearest neighbour pairs suggest that intraspecific competition and interspecific facilitation determine D. cymosum woody plant community structure. This study had limited application to rangeland management. However, it can be concluded that grazing of D. cymosum communities should take place during mid-summer, when enough grazing material is available to allow animals to vary their diet. The introduction of animals in poor condition or naïve animals into these lands should be avoided in winter and spring as they will graze non-selectively resulting in D. cymosum poisoning. To utilize these areas as grazing lands, supplements need to be provided to assist in the detoxifications of toxins once ingested. / Dissertation (MSc Agric)--University of Pretoria, 2013. / gm2014 / Plant Production and Soil Science / unrestricted

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In the first part of the thesis, the spontaneous occurrence of an outbreak of chronic aflatoxicosis is reported in dairy calves. Forty 4-month-old male Holstein calves of approximately 100kg were fed a ration constituted by alfalfa hay, broken corn and milk substitute. Six calves (15%) died after presenting a disease characterized by general unthriftiness, diarrhea, rough hair coats, abdominal pain, prolapsed rectum and grinding of teeth. The clinical course, was 2-3 days; however many calves in this lot that did not die, remained underdeveloped. Three calves were necropsied. Necropsy findings included firm, light tan livers and marked hydrothorax, ascites and edema of the mesentery, mesocolon and of the mucosal folds of the abomasum. Main histopathological changes were restricted to the liver and consisted of fibrosis, moderate megalocytosis, biliary duct hyperplasia and venoocclusive disease. The analysis by thin layer chromatography of the corn fed to calves revealed 5,136 ppb of aflatoxin B1. A diagnosis of aflatoxicosis was made based on the characteristic clinical signs and pathology, on the absence of Senecio spp. in the food and on the presence of high levels of aflatoxin in the corn fed to the calves. In the second part of the thesis, two experiments were performed in order to determine the toxic effects of varying doses of aflatoxins in calves. Clinical, productive and pathologic aspects of affected calves were considered. In the first experiment, nine 2-4- month old calves Holstein Friesian calves were fed, for two months, daily amounts corresponding to 1.5% of their body weight of a ration containing 500±100 ppb of aflatoxins. Three calves were used as controls. In the second experiment, three 4-5-month old Holstein Friesian calves, were orally fed daily small parcels of a concentrate of aflatoxins diluted in 500 ml of water corresponding to 1,250, 2,500 e 5,000 ppb of B1 aflatoxin (AFB1). A male calf was used as control. During all the experimental period of the first experiment, the weight gain of the calves receiving AFB1 was equivalent to that of the control group and no differences were observed between treated and control calves when the values of serum activity of aspartate transaminase (AST), serum albumin (SA), total serum protein (TP), and PVC, determined weekly, were compared. A significant difference in the serum activities of alkaline phosphatase (AP) and gamma glutamyl transferase when the serum sampled on the 63th day of the experiment was considered. During the whole experimental period and up to three weeks after the final of the experiment, no clinical signs or histopathological changes associated with the consumption of aflatoxins were observed in any of the calves of the first experiment. In the second experiment, clinical signs observed in three treated calves included loss of appetite, decrease in weight gain, and loss of weight Jaundice, intermittent diarrhea, tenesmus and apathy were only observed in the calf receiving 5,000 ppb of AFB1. Increased activity of AF and GGT were observed in all the calves of the treated group. No changes were observed regarding PCV, TP, total bilirubin, direct bilirubin and in the serum activity of AST in any of the calves of the second experiment. Histopathological changes in intoxicated calves included bile duct proliferation, cytoplasmic vacuolar hepatocelular degeneration consistent with hepatocelular deposit of lipids, periportal to bridging fibrosis, megalocytosis, subendothelial edema and fibrosis in terminal hepatic veins. Necropsy findings in the euthanatized calf which receive de largest doses of AFB1 included slight enlargement of the liver which was firm and diffusely light-yellow, mild ascites, and edema of the mesentery and of abomasal folds. / Na primeira parte dessa tese, relatamos a ocorrência de um surto de aflatoxicose crônica bezerros de raça leiteira. Quarenta bezerros holandeses, machos, de quatro meses de idade e aproximadamente 100 kg eram alimentados com feno de alfafa, milho quebrado e substituto de leite. Seis bezerros (15%) morreram após apresentar uma doença caracterizada por mau desenvolvimento geral, diarreia, pelagem áspera, dor abdominal, tenesmo, prolapso de reto e bruxismo. A duração do curso clínico foi de 2-3 dias; muitos terneiros desse lote que não morreram permaneceram pouco desenvolvidos. Os achados de necropsia de três bezerros incluíam fígado firme e castanho-claro, marcados hidrotórax e ascite, e edema do mesentério, mesocólon e das dobras da mucosa do abomaso. Os principais achados histopatológicos estavam restritos ao fígado e consistiam de fibrose, moderada megalocitose, hiperplasia de ductos biliares e lesão veno-oclusiva. A análise do milho do alimento dos bezerros por cromatografia de camada delgada revelou 5.136 ppb de aflatoxina B1 (AFB1). O diagnóstico de aflatoxicose foi feito baseado nos sinais clínicos e patologia característicos, na ausência de Senecio spp. na alimentação dos terneiros e na presença de altos níveis de aflatoxina no milho da alimentação dos bezerros. Na segunda parte da tese, dois experimentos foram realizados para determinar os efeitos tóxicos de diferentes doses de aflatoxinas em bezerros, considerando-se aspectos clínicos, produtivos e patológicos. No primeiro, nove bezerros, Holandês, com 2-4 meses de idade, receberam ração contendo 500±100 ppb de aflatoxina, na quantidade equivalente a 1,5% do peso vivo/dia, durante dois meses. Três bezerros foram usados como controle. No segundo experimento, três bezerros, Holandês, com 4-5 meses de idade, receberam, por via oral, pequenas porções diárias de um concentrado de aflatoxinas, diluídas em 500 ml de água, correspondendo a doses de 1.250, 2.500 e 5.000 ppb de AFB1. Um bezerro foi usado como controle. No primeiro experimento, o ganho de peso dos bezerros recebendo AFB1 foi equivalente ao do grupo controle durante todo período experimental e não foram observadas alterações na atividade sérica da enzima aspartato transaminase (AST), da albumina sérica (AS), da proteína total (PT) e no hematócrito, quando comparados os resultados semanais do grupo tratamento e controle. Diferenças significativas nas atividades séricas das enzimas fosfatase alcalina (FA) e gama glutamil transferase (GGT) ocorreram na coleta do 63º dia do experimento. Não foram observados sinais clínicos e alterações histopatológicas de aflatoxicose em qualquer dos bezerros do grupo tratamento desse experimento. No segundo experimento, sinais clínicos observados nos bezerros intoxicados incluíram perda de apetite, diminuição do ganho de peso e emagrecimento. Icterícia, diarreia intermitente, tenesmo e apatia severa, foram observadas apenas em um bezerro (5.000 ppb de AFB1). Níveis alterados da atividade sérica de FA e GGT foram observados em todos os bezerros do grupo tratamento. Não foram observadas variações no hematócrito e na atividade sérica de AST, nem nos níveis séricos de PT, bilirrubina total e bilirrubina direta em qualquer dos bezerros desse experimento. Alterações histopatológicas nos bezerros intoxicados incluíram proliferação de ductos biliares, degeneração citoplasmática vacuolar consistente com acumulação hepatocelular de lipídios, fibrose periportal, ou em ponte, megalocitose, fibrose subendotelial das veias hepáticas terminais e edema. Achados de necropsia do bezerro recebendo a maior dose de AFB1 incluíram fígado levemente aumentado de tamanho, difusamente amarelo-claro e firme, discreta ascite, edema de mesentério e submucosa do abomaso.