Biological, physiological and pathogenic variation in a genetically homogenous population ofFusarium oxysporumf.sp.cubense

Abstract

Fusarium oxysporum f.sp. cubense (Foc) is the causal agent of Fusarium wilt of banana and is divided into three races and 21 vegetative compatibility groups (VCGs). Within a VCG, Foc proved to be genetically homogenous. Previous studies on phenotypic characteristics were performed with isolates that represented different races and VCGs from different banana-producing countries. The aim of this study was to determine the phenotypic variation in a genetically similar South African population of Foc, where all isolates belong to VCG 0120. Twenty-six isolates of Foc ‘subtropical’ race 4 (VCG 0120) were selected for this study. Differences in growth rate, spore production and the number of spores were determined. Virulence of Foc isolates was determined by inoculating susceptible, tissue-cultured, banana plantlets. Differences in cultural characteristics and virulence among isolates were found. The South African isolates can be divided into sporodochial, cottony and slimy pionnotal types. All isolates produced microconidia in abundance, but production of macroconidia and sporodochia varied. Disease severity varied from no vascular discoloration to complete discoloration of vascular tissue. This study showed that, although the South African population of Foc is homogenous in terms of its genetic make-up, it varies considerably in terms of phenotypic characteristics.