Race Differentiation in F usarium oxysporum f.sp. chrysanthemi

The pathogenicity of different isolates of F usarium oxysporum obtained from plants of Gerbera ( G erbera jamesonii ), Chrysanthemum ( C hrysanthemum morifolium ), P aris daisy ( A rgyranthemum frutescens ) and African daisy ( O steospermum sp.), all in the family Asteraceae, was tested on different cultivars of these hosts, to assess their pathogenicity. The reactions were compared with those of isolates of F . oxysporum f. sp. chrysanthemi and of f.sp. tracheiphilum obtained from the A merican T ype C ulture C ollection. We found that isolates of F . oxysporum f. sp. chrysanthemi can be distinguished as three physiological races on the basis of their pathogenicity to the panel of differential cultivars. Sequencing of the intergenic spacer ( IGS ) region of ribosomal DNA (r DNA ) and phylogenetic analysis showed that the F usarium races fell into three phylogenetic groups, which coincided with those observed in pathogenicity tests. Analysis of the IGS sequences revealed a high degree of similarity among strains from I taly and S pain from different host species, suggesting that recent outbreaks in these ornamentals were probably caused by introduction of infected nursery material from a common origin.