Tomato Spotted Wilt Virus: TSWV in Vegetable Crops: Tospoviruses

Tospoviruses In Solanaceae and Other Crops in The Coastal Plain of Georgia

History

Alex Csinos, Natalia Martinez

Tospoviruses are the only plant infecting members of the Bunyaviridae family. Most Bunyaviruses involve an insect vector, which spreads the virus between hosts. This is also the case with tospoviruses where several different species of thrips (Thysanoptera) serve as vectors. In the United States the main vectors are Frankliniella occidentalis, F. fusca and Thrips tabaci. Of these F. occidentalis, the western flower thrips, has the broadest host range affecting a diverse variety of ornamental and vegetable crops. F. fusca has proven economically important as a vector in the peanut and tobacco industry and T. tabaci vectors a strain of tospovirus in onion and garlic crops (Campbell et al., 2005). There are new tospoviruses being reported all the time, but the current list includes 16 tospovirus species. In the United States, however, only Tomato spotted wilt virus, Impatiens necrotic spot virus and Iris yellow spot virus have been reported. The host range varies for each tospovirus species and worldwide the total number of reported susceptible hosts includes 848 named plant species within 106 identified families.

Tomato spotted wilt virus was first reported in Georgia in 1986, but was not considered a problem until 1989. The disease infects many of the commercial crops in Georgia and also many of the weeds found in the Coastal Plain in Georgia. Three of the reported vectors of TSWV Frankliniella fusca (Hinds) (Sakimura, 1963), F. occidentalis (Pergande) (Sakimura, 1962), and F. bispinosa Morgan (Webb et al., 1997) are present in Georgia. The wide host range of both the virus and thrips vectors makes managing the disease very difficult. The most effective way to minimize the impact of spotted wilt is by use of resistant cultivars. Significant progress has been made in developing such cultivars for peanuts, tomato and peppers. However, in the case of flue-cured tobacco, no resistance has yet been identified in commercial cultivars. Efforts to deploy other control options such as insecticide sprays, adjusting planting dates, rouging of infected plants, and replanting have had limited and unpredictable results on reducing TSWV infections.

The incidence of TSWV in tobacco was light from 1989 through 1994, with incidence being traced to a few percent state wide. However, in 1995 to present, the level of TSWV incidence increased dramatically (Fig.1). Coincidentally, those were the drought years experienced in Georgia (see environment). More recently, the level of TSWV has been consistently high (>30%) and it has been common for entire fields to be destroyed by the virus.

Impatiens necrotic spot virus (INSV) was first reported in Impatiens sp. (Law and Moyer, 1990). INSV is closely related to TSWV, and was initially designated as TSWV-I, but later named as a separate species in the genus Tospovirus. INSV is an emerging virus found mostly in ornamentals under greenhouse production (Daughtrey et al., 1997). Field crops are also susceptible to INSV, but fewer reports have been made. INSV was first detected in peanut growing during 1998 in Georgia (Mitchell and Tift counties) and Texas (Frio County) (Pappu et al., 1999). Tomato and pepper (Naidu et al. 2005) are also hosts for INSV, although symptoms are less severe than with TSWV. Little is known about INSV distribution and impact on outdoor vegetable and field crops, but recent field surveys suggest that incidence of INSV in peanut might be increasing in mixed infections with TSWV or alone (Wells et al., 2001; Martinez-Ochoa et al., 2002). INSV has also been found in flue-cured tobacco (Martinez- Ochoa et al., 2003), yellow and purple nutsedge (Martinez-Ochoa et al., 2004), and several other weeds such as wandering cudweed, bristly starbur, smallflower morningglory, common ragweed, spiny sowthistle, dogfennel, etc. (Martinez-Ochoa et al., unpublished). For several years it was believed that Frankliniella occidentalis was the only confirmed vector of INSV (Peters et al., 1996), but more recently F. fusca has been shown to serve as a vector as well (Naidu et al., 2001). Figure 1. Tobacco losses attributed to TSWV

Figure 1. Tobacco losses attributed to TSWV

top