Abstract
BackgroundFusarium wilt, caused by the fungal pathogen Fusarium oxysporum f. sp. cubense (Foc), is one of the most destructive diseases of banana. Toxins produced by Foc have been proposed to play an important role during the pathogenic process. The objectives of this study were to investigate the contamination of banana with toxins produced by Foc, and to elucidate their role in pathogenesis.Methodology/Principal FindingsTwenty isolates of Foc representing races 1 and 4 were isolated from diseased bananas in five Chinese provinces. Two toxins were consistently associated with Foc, fusaric acid (FA) and beauvericin (BEA). Cytotoxicity of the two toxins on banana protoplast was determined using the Alamar Blue assay. The virulence of 20 Foc isolates was further tested by inoculating tissue culture banana plantlets, and the contents of toxins determined in banana roots, pseudostems and leaves. Virulence of Foc isolates correlated well with toxin deposition in the host plant. To determine the natural occurrence of the two toxins in banana plants with Fusarium wilt symptoms, samples were collected before harvest from the pseudostems, fruit and leaves from 10 Pisang Awak ‘Guangfen #1’ and 10 Cavendish ‘Brazilian’ plants. Fusaric acid and BEA were detected in all the tissues, including the fruits.Conclusions/SignficanceThe current study provides the first investigation of toxins produced by Foc in banana. The toxins produced by Foc, and their levels of contamination of banana fruits, however, were too low to be of concern to human and animal health. Rather, these toxins appear to contribute to the pathogenicity of the fungus during infection of banana plants.
Highlights
The genus Fusarium comprises a large number of plantassociated fungal species with the potential to cause economic damage and reduce the quality of agricultural crops
Banana Fusarium wilt is widely believed to be caused by the colonization of the root, rhizome and pseudostem xylem vessels with Foc, and the subsequent blockage of the vascular system which eventually results in plant death [39]
Both fusaric acid (FA) and BEA can kill banana cell and protoplast, and at tissue levels, the symptoms include the rotting of roots and pseudostems, and the wilting of leaves of seedlings when applied at high concentrations
Summary
The genus Fusarium comprises a large number of plantassociated fungal species with the potential to cause economic damage and reduce the quality of agricultural crops. These include wilt pathogens such as F. oxysporum and F. solani, both which cause the eventual demise of their plant hosts, and mycotoxin-producers such as F. graminearum and F. verticillioides, which contaminate food and feed with secondary metabolites (mycotoxins) harmful to humans and animals. Numerous mycotoxins and phytotoxins produced by Fusarium species have been described, along with their potential to cause disease to plants and animals [1]. Toxins produced by Foc have been proposed to play an important role during the pathogenic process. The objectives of this study were to investigate the contamination of banana with toxins produced by Foc, and to elucidate their role in pathogenesis
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