|Marasas, Walter F|
|De Vos, Lieschen|
Submitted to: Mycopathologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2010
Publication Date: 10/1/2010
Citation: Moses, L.M., Marasas, W.0., Vismer, H.F., De Vos, L., Rheeder, J.P., Proctor, R., Wingfield, B.D. 2010. Molecular characterization of Fusarium globosum strains from South African maize and Japanese wheat. Mycopathologia. 7(4):237-249. Interpretive Summary: The results of this research provide a possible explanation for why some strains of the fungus Fusarium globosum produce toxins known as fumonisins and others strains do not. Fumonisins are frequent contaminants of corn kernels in many regions of the world. Ingestion of contaminated kernels can cause multiple animal diseases, including cancer and neural tube defects in rodents. In addition, there are medical studies that indicate a correlation between consumption of fumonisin-contaminated corn and esophageal cancer and neural tube defects in some human populations for which corn is a dietary staple. Fusarium globosum has been isolated from wheat in Japan and corn in South Africa. The results of this study, demonstrate that the isolates from Japan do not produce fumonisins and lack one of the genes that is required for fumonisin synthesis in fungi. In contrast, the South African isolates of the fungus can produce fumonisins and have the gene that is absent in the Japanese isolates. The two groups of isolates also exhibit other growth and genetic differences. These findings provide information that agriculture and health officials can use to assess risk of fumonisin contamination posed by F. globosum.
Technical Abstract: The fungus Fusarium globosum was first isolated from maize in South Africa and subsequently from wheat in Japan. Here, multiple analyses revealed that, despite morphological similarities, South African maize and Japanese wheat isolates of the fungus exhibit multiple differences. An AFLP-based similarity index for the two groups of isolates was only 45%. Most maize isolates produced relatively high levels of fumonisins, whereas wheat isolates produced little or no fumonisins. The fumonisin biosynthetic gene FUM1 was detected in maize isolates by Southern blot analysis but not in the wheat isolates. In addition, most of the maize isolates produced sclerotia and all of them produced large orange to dark purple sporodochia in carrot agar culture, whereas wheat isolates did not produce either structure. In contrast, individual isolates from both maize and wheat carried markers for both mating type idiomorphs, which indicates that the fungus may be homothallic. However, a sexual stage of F. globosum was not formed under standard self-fertilization conditions developed for other homothallic species of Fusarium. The inability to produce the sexual stage is consistent with the high similarity of 87– 100% and GST index of 1.72 for the maize isolates, which suggests that these isolates are undergoing asexual but not sexual reproduction. Together, the results suggest that the South African maize and Japanese wheat isolates of F. globosum are distinct populations and could be different species.