The Identification of the Vector Species of Iris Yellow Spot Tospovirus Occurring on Onion in Brazil

Abstract

In Brazil, tospoviruses have been reported in several horticultural and ornamental plants. In the northeast region of Brazil, a tospovirus has emerged as a devastating virus on onion cultures. Based on serology and the sequence of nucleocapsid (N) protein gene, this pathogen was identified as a strain of iris yellow spot tospovirus (IYSV) (1). This virus was first identified on iris and leek in The Netherlands and later on onion in Israel. For an effective integrated management of tospoviruses in Brazil, identification of IYSV vector is essential. Three thrips species, Thrips tabaci, Frankliniella schultzei, and F. occidentalis, that are major vegetable and floral crop pests in the Federal District, Brazil, were tested for their ability to transmit the virus by leaf disk assay (2). All thrips, up to 8 h old, were given an acquisition access period of 48 h at 25°C on IYSV-infected Nicotiana benthamiana plants in Tashiro-cages. Thrips were then reared on uninfected Datura stramonium detached leaves until the adult stage. These adults were transferred individually to microcentrifuge tubes containing an N. benthamiana leaf disk and were incubated for 48 h for virus inoculation. The leaf disks were then incubated 4 more days to allow development of the virus infection, and the presence of virus was evaluated by Dot-enzyme-linked immunosorbent assay (Dot-ELISA) with polyclonal antibodies against N protein of IYSV. Adult thrips were also used for direct inoculation to N. benthamiana plants, three thrips per plant. By the leaf disk assay, 45.8% (22 out of 48) of T. tabaci transmitted the virus, but F. schultzei (n = 48) and F. occidentalis (n = 32) did not transmit it. All plants (4 out of 4) directly inoculated by T. tabaci showed symptoms and infection by Dot-ELISA, while no plants inoculated with F. schultzei (n = 5) and F. occidentalis (n = 3) were positive, either by symptom observation or by Dot-ELISA. Only T. tabaci showed potential for a high capacity to transmit the IYSV onion isolate. In the field, considering the host preference of thrips, T. tabaci was considered the most important vector species of IYSV on onion. References: (1) L. Pozzer et al. Plant Dis. (In press.) (2) I. Wijkamp and D. Peters. Phytopathology 83:986, 1993.

Analysis of Iris yellow spot virus replication in vector and non‐vector thrips species

“…Similar observations were reported on the vector capability of IYSV by T. tabaci (Jenser et al ., ). The specificity of T. tabaci to transmit IYSV observed in this study is well documented (Nagata et al ., ; Kritzman et al ., ; Whitfield et al ., ). The other two thrips species and their colour forms were not able to transmit IYSV to onion plants despite their ability to feed on the infected plants.…”

“…This is in agreement with an earlier report by Nagata et al . () who identified T. tabaci as the only vector of IYSV. Tospoviruses are believed to enter the midgut epithelial cells via cellular receptor‐mediated endocytosis or membrane fusion (Bandla et al ., ; Kikkert et al ., ; Medeiros et al ., ).…”

The competence of four thrips species to transmit and replicate four tospoviruses

“…The population of T. tabaci in the present study, which was also thelytokous, transmitted neither TSWV nor the other three tospoviruses. Interestingly, this population was an efficient vector of Iris yellow spot virus , a tospovirus occurring on onion in Brazil (Nagata et al. , 1999a).…”

Sources of Iris yellow spot virus in New York

“…More specific studies have confirmed that IYSV is not known to be transmitted through onion seed (25,40), and the only confirmed vector for plant-toplant spread of IYSV is the onion thrips, Thrips tabaci (Lindeman) (6,25,30). appears to hold true for the onion-IYSV-thrips pathosystem.…”