Characterisation of South African isolates of Fusarium oxysporum f.sp. cubense from Cavendish bananas

Abstract

Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f.sp. cubense (Foc), is a serious vascular disease of bananas in most subtropical and tropical regions of the world. Twenty-four vegetative compatibility groups (VCGs) and three pathogenic races have been identified in Foc, reflecting a relatively high genetic diversity for an asexual fungus. To characterise a South African population of Foc, a collection of 128 isolates from diverse geographic origins were isolated from diseased Cavendish bananas and subjected to VCG analysis and sequencing of the translation elongation factor 1-α (TEF) gene region. The presence of mating type genes was also determined using MAT-1 and MAT-2 specific primers. VCG 0120 was established as the only VCG of Foc present in the South African population studied. Only the MAT-2 idiomorph was present in all the local isolates of Foc. A phylogenetic analysis of DNA sequences of the TEF gene region revealed that the South African isolates grouped closely with VCG 0120 isolates from Australia and Asia. These results suggest that the South African population of Foc was most likely introduced in a limited number of events and that it had spread with infected planting material within the country. The presence of only one mating type and the limited diversity in this pathogen render it unlikely to rapidly overcome disease management strategies involving host resistance.