SUMMARY

A fragment of the NSM gene of naturally occurring Tomato spotted wilt virus (TSWV) isolates recovered in Apulia (southern Italy) from different cultivated and wild plant species was amplified by RT-PCR. The re-sulting 670 bp amplicon was cloned, sequenced and compared with available NSM sequences of other tospoviruses. The primary nucleotide sequence was 94.3 to 100 % identical in all the Apulian TSWV iso-lates and had a 94-99 % identity with TSWV-BR01, TSWV-L3, TSWV-JP, TSWV-A and TSWV-D. With other tospoviruses, sequence identity was in the range of 81-83 % with Tomato chlorotic spot virus and Chrysanthemum stem necrosis virus and, 74-79 % with Groundnut ring spot virus, Zucchini lethal chlorosis virus and Impatiens necrotic spot virus, 53-55 % with Iris yel-low spot virus, Peanut bud necrosis virus and Watermel-on silver mottle virus. The phylogenetic tree showed three primary branches departing from the bulk of all NSM sequences; all the TSWV sequences clustered in two subgroups, denoted A-like and D-like, clearly dis-tinct from the other tospoviruses. The inclusion in a group of any of the Apulian isolates of TSWV was ap-parently not determined by the year, the place or the host from which they were recovered. The A-like iso-lates clustered with TSWV-A, an isolate that was able to overcome host and pathogen-mediated resistance in tomato whereas the remaining six isolates clustered with TSWV-D, an isolate that did not overcome these forms of resistance. A simple and rapid procedure based on RT-PCR followed by enzymatic digestion was developed to identify isolates of the two subgroups