ABSTRACT
Fungi synthesise a diverse array of secondary metabolites, some of which are known to be toxic to plants, animals and humans. Certain species of Cochliobolus, Alternaria, Pyrenophora, Septoria and Periconia produce metabolites which have been definitively linked with specific plant diseases and are, consequently, regarded as host-specific toxins. Other fungi, including particular species of Rynchosporium, Fusarium, Alternaria, Fusicoccum and Exserohilum synthesise non-specific toxins, some of which may act as virulence factors in plant disease. Many plant pathogenic species of Aspergillus, Penicillium, Fusarium and Alternaria also produce metabolites with the potential to precipitate disease in animals and humans. These substances are known as mycotoxins. Following infection with these fungi, plant products such as seeds and fruit regularly become contaminated with mycotoxins which may then directly or indirectly enter the human food chain. Forages infected with particular species of Acremonium, Phomopsis and Pithomyces may also contain mycotoxins capable of causing disease in ruminant animals. Mycotoxins commonly occur in the spores of fungi, including those emanating from Stachybotrys and Alternaria and inhalation, therefore, represents another route of entry into the body. Although mycotoxins have been implicated in many animal and human disorders, it is their carcinogenic potential which has evoked global concern. In addition, recent findings linking mycotoxins with neurotoxic, hepatotoxic and immunosuppressive effects have provided the impetus for continued monitoring and research. Some mycotoxins are associated with profound reproductive disorders in animals but the implications for human fertility need to be addressed. Mycotoxins may be regarded as unavoidable contaminants of food and feed even when good farming and manufacturing practices have been implemented. Regulation of maximum permissible levels is effected by a combination of legislative and advisory measures and is an area of continuing activity. Recent field trials have failed to provide a consensus regarding the efficacy of fungicides to control mycotoxin production. In addition, the development of fungicide-resistant strains of Fusarium is causing some concern with respect to potential changes in the pattern and levels of mycotoxin production. It would appear, therefore, that attempts to exploit disease-resistant plant genotypes represent a more promising strategy for further reductions in mycotoxin contamination of primary food commodities.
