SUMMARY

A sequence-specific amplified polymorphism (SSAP) technique was developed to study the clonality of Fusar-ium oxysporum f.sp. lactucae VCG 0300 which causes Fusarium wilt of lettuce. Specific primers designed from two known long terminal repeats (LTRs) of the F. oxys-porum genome were coupled with MseI AFLP-derived primers to investigate the level of polymorphism in 80 isolates of F. oxysporum obtained from different loca-tions worldwide. The technique proved to be reliable, efficient and able to discriminate among F. oxysporum f.sp. lactucae race 1 strains and a single strain of race 2. Polymorphisms within Italian and US race 1 isolates were detected but no relation was found between genet-ic variability and geographic distribution of strains. The technique confirmed the worldwide clonality of VCG 0300 race 1. In addition, the present study revealed that the SSAP technique can be used for reliable strain dis-crimination and as a tool to investigate transposition be-haviour of retroelements in the genome of the pathogen. Key words: Diagnostics, molecular characterization, long terminal repeats (LTRs), SSAP, Fusarium wilt, let-tuce