THE BIOLOGICAL PROPERTIES OF A DISTINCT TOSPOVIRUS AND SEQUENCE-ANALYSIS OF ITS S RNA

A tospovirus isolate from Brazil, designated TSWV-B, was first identif ied as a unique isolate based on our observation that transgenic plant s expressing the N gene of the lettuce strain of tomato spotted wilt v irus (TSWV-BL) were susceptible to TSWV-B but showed resistance to bot h TSWV (L type) and impatiens necrotic spot virus (INSV). TSWV-B was s erologically distinct from TSWV and INSV. TSWV-B generally incited sym ptoms resembling those caused by other TSWV isolates, except TSWV-B sy stemically infected Petunia hybrida, which is a local-lesion host of T SWV. Unlike the cucurbit isolate TSWV-W, TSWV-B did not infect Cucumis sativus and only occasionally induced systemic infections on C metuli ferus. The complete nucleotide sequence of the S RNA of TSWV-B was det ermined with cDNA clones to be 3,049 nucleotides long. The genome orga nization of this S RNA was similar to those of TSWV and INSV. The alig nment of the S RNA nucleotide and deduced amino acid sequences with th e homologous sequences of TSWV (isolates CNPH1, L3, and BL) and INSV r evealed that TSWV-B was related more closely to all the TSWV isolates than to INSV. There was a higher degree of identity among the TSWV iso lates than with TSWV-B. Thus, TSWV-B appears to be a distinct tospovir us; however, a precise classification requires additional biological a nd molecular information on this isolate as well as comparison to othe r tospovirus isolates.