Peanut; Potato; Tomato

Orthotospoviruses are transmitted by thrips (Thysanoptera) insects. Frankliniella fusca (tobacco thrips), F. occidentalis (western flower thrips), F. schultzei (common blossom thrips), Scirtothrips dorsalis (chilli thrips), Thrips palmi (melon thrips), and T. tabaci (onion thrips) are known vectors of GBNV (Manjunatha, 2008; Pranav and Krishnaraj, 2010).

No specific signs are present.

In general, symptoms of GBNV infection, which include chlorosis, mottle, lesions, stunted growth, necrotic rings, and bud necrosis, are very similar regardless of the infected host or virus isolate (Mandal et al., 2012).

In peanut: "Initially, mild chlorotic spots appear on young quadrifoliate leaves, and subsequently necrosis and chlorotic rings develop. In rainy and post-rainy seasons, necrosis of the terminal bud is the main characteristic symptom. Secondary symptoms such as stunting, axillary shoot proliferation, and malformation of leaflets are common. Plants infected early are bushy, stunted, and die prematurely. If plants older than one month are infected, the symptoms are restricted to a few branches only" (Mandal et al., 2012).

In tomato: Symptoms include necrotic rings on leaf, stem necrosis, concentric rings and patchy color on fruit (Manjunatha, 2008; Mandal et al., 2012). Necrosis of the foliage often leads to collapse of a stem or of the whole plant resembling symptoms of blight. In general, tomato plants infected at an early stage often collapse and die. (Akram et al., 2012).

In potato: Symptoms of infection are characterized by stem/petiole necrosis, foliar spotting/deformation/necrosis and stunting of the plant (Kaushal et al., 2010). Necrosis of foliage often leads to collapse of a stem or the entire plant. In general, potato plants infected at an early stage often collapse and die. (Akram et al., 2012; Pundhir et al., 2012).

In bean, pea, and other legumes: GBNV infection induces chlorotic and necrotic spots on leaves, browning in veins, stem necrosis, ring spots on fruits and pods (Akram et al., 2012).

Serological:

A field-based screening method/assay (ELISA) is commercially available for GBNV (at the serogroup IV level) from Agdia.

Note: This ELISA kit detects both Watermelon silver mottle virus (WSMoV) (not known to occur in the United States) and Groundnut bud necrosis virus and (GBNV) at the same time. The ELISA kit is specific to test WSMoV, GBNV and other potential serogroup IV of orthotospoviruses. In addition, it gives no cross-reaction with other orthotospoviruses known to occur in the United States such as Impatiens necrotic spot virus (INSV), Tomato spotted wilt virus (TSWV), Groundnut ringspot virus (GRSV), Tomato chlorotic spot virus (TCSV), or Iris yellow spot virus (IYSV).

It is possible that the specific ELISA kit for WSMoV and GBNV will cross-react with Capsicum chlorosis virus (CaCV) and Watermelon bud necrosis virus (WBNV). Although this specific ELISA kit could possibly react with CaCV and WBNV, in addition to the desired GBNV, these viruses (CaCV and WBNV) are not present in the United States. Hence, the cross-reactions with close-related orthotospoviruses in the same serogroup (IV) during the survey are not a major concern.

Confirmation, however, requires a combination of molecular techniques.

There are several other orthotospovirus species which infect the same hosts as GBNV, and at least two are present in the United States. For example, Groundnut ringspot virus (GRSV) and Tomato spotted wilt virus (TSWV) cause similar symptoms in tomato, are present in the United States, and are also vectored by Frankliniella occidentalis and F. schultzei (Webster et al. 2010; Reitz et al., 2011).

Other orthotospovirus species which infect solanaceous hosts and are also vectored by thrips include: Capsicum chlorosis virus (CaCV), Groundnut yellow spot virus (GYSV), Peanut chlorotic fan-spot virus (PCFV), Tomato chlorotic spot virus (TCSV), and Tomato yellow ring virus (TYRV) (Reitz et al., 2011). Molecular identification is necessary for confirmation of GBNV.

There are numerous publications which describe serological/ molecular diagnostic methods for GBNV.

Jain et al. (2005) created a high titre polyclonal antiserum to the nucleocapsid protein of GBNV that can successfully detect GBNV infection via a DAC-ELISA in a wide range of hosts, including cowpea, mungbean, soybean, tomato, and urdbean. However, this assay could not distinguish among the different orthotospoviruses in serogroup IV, such as Watermelon bud necrosis virus (WBNV) and Capsicum chlorosis virus (CaCV).

Akram et al. (2004) identified GBNV using an RT-PCR. The primers were developed based on the sequence of the movement protein (NSm) of the virus. Pundhir et al., (2012) developed an RT-PCR using primers targeting the nucleocapsid protein of GBNV. Kaushal et al. (2010) developed a print capture RT-PCR (PC-RT-PCR) which diagnosed GBNV infection in potato and in thrips insect vector tissue.

Maheshwari et al. (2015) developed a single chain variable fragment (scFv) for specific diagnosis of GBNV. This scFv was able to detect GBNV via DAC-ELISA and immunocapture RT-PCR (IC-RT-PCR). The IC-RT-PCR was able to distinguish GBNV from the closely related WBNV