Presence of putative pathogenicity genes in Fusarium oxysporum f.sp. cubense

Fusarium wilt is caused by a range of ‘formae speciales’ of Fusarium oxysporum which are classified according to the host plant genera to which they are specialised. Fusarium wilt of banana (Musa spp.) occurs when Fo f.sp. cubense (Foc) invades the vascular system via the roots, inevitably leading to plant death. Foc is further divided into races, each of which affects a different range of banana cultivars. Race 4 is the most important as it has the widest host range and is the only race known to be a competent pathogen of the commercially significant Cavendish cultivars. Previously, researchers have identified pathogenicity genes in Fo f.sp. lycopersici (Fol),based on proteins ‘secreted in xylem’ upon infection of tomato plants; these are SIX1 to SIX8 genes. The aim of the research reported here was to determine if SIX genes were present in Foc and identify differences in the SIX gene profiles among the different races of Foc. These studies have revealed the presence of SIX7 and SIX8 genes in race 4 isolates of Foc, which are absent in race 1 and 2 isolates. The results suggest that if these genes have a similar role in Foc as they do in Fol, then SIX7 and SIX8 genes may have a role in Cavendish infection and contribute to the broader host range of Foc race 4.