ABSTRACT
Tomato spotted wilt virus (TSWV) is the type member of the genus Tospovirus, the only plant-infecting virus group within the family Bunyaviridae. TSWV was reported infecting several horticultural crops, but the disease became significant in the 1980s when severe epidemics were observed worldwide and it was considered one of the ten most economically destructive plant viruses. In this expansion, the worldwide distribution of its vector the western flower thrips (Frankliniella occidentalis) played the central role beside its extremely broad host range. Tospoviruses are unique in that they can replicate both in plant and insect hosts. The viral genome consists of three single-stranded RNA molecules: a large (L RNA), a medium (M RNA), and a small (S RNA) segment of negative or ambisense polarity (respectively), which enables the virus to develop reassortants. From the S RNA, two proteins are translated: the nucleocapsid (N) and a nonstructural protein (NSs) that functions as a silencing suppressor and avirulent determinant in TSWV-pepper interaction. Biologically distinct isolates of TSWV exist in nature. The driving force for the rapid adaptation of TSWV and for its variability is the high frequency of mutation, reassortment, and recombination. On the basis of N protein sequences, tospoviruses are divided in two main geographical groups: Asian and American. Effective disease management against TSWV requires multicomponent approaches. The approaches are mainly based on avoidance of sources of infectivity, control of vectors, and use of resistant varieties. Of primary importance is the use of virus-free propagating material and effective control of natural weed hosts of TSWV, especially those on which thrips vectors multiply. The efficient way to fight against a virus disease is to increase crop resistance. Generally, two forms of resistance exist. One is to use transgenic plants, and the other is to use resistance gene in traditional crossing methods. Even when a Tsw resistance gene was introduced into several pepper varieties, TSWV was able to adapt very rapidly to plant resistance, and the Tsw resistance was broken down only a few years after its deployment in pepper breeding.
