Characterization of iris yellow spot tospovirus
In the Netherlands, disease symptoms have occasionally been observed in Iris hollandica since 1992. Symptoms were characterized by chlorotic spots which later developed into yellow and necrotic spots. Depending on the iris cultivars, the percentage of infected plants ranged from 5 to 90 %. Serological comparisons and sequence determination demonstrated that the causal agent is a new and distinct tospovirus. Electron microscopy also revealed the presence of spherical particles (80 to 120 nm), characteristic of tospoviruses. The name iris yellow spot tospovirus has been proposed. The experimental host range is narrow, it includes Nicotiana tabacum and Datura stramonium. The natural host range could include other monocotyledons (e.g. onion, leek, lily) and it can be noted that this virus has been observed in Israel on field-grown onions (EPPO RS 98/092). Concerning thrips transmission, no transmission was obtained with Frankliniella occidentalis but T. tabaci is suspected as a vector (in diseased iris fields in the Netherlands and onion fields in Israel, T. tabaci infestations were observed).
In the north-east region of Brazil (S-o Francisco River basin) a tospovirus has emerged as a devastating virus on onion. It was at first designated as BR-10 (see EPPO RS 96/198) and was recently identified and characterized as a strain of iris yellow spot tospovirus. In Brazil, this tospovirus causes a disease known as 'sapeca', and affected onion plants show numerous eyelike spots on the leaves and flower stalks resulting in flower abortion. It is noted that the economic impact of iris yellow spot tospovirus in iris and onion is low in the Netherlands but this is not the case in Brazil on onion, as up to 100% loss has been observed in onion fields. Concerning thrips vectors, it has been shown in Brazil that only Thrips tabaci could transmit the disease, and that Frankliniella schultzei and F. occidentalis were not vectors.
Sources
Cortês, I.; Livieratos, I.C.; Derks, A.; Peters, D.; Kormelink, R. (1998) Molecular and serological characterization of iris yellow spot virus, a new and distinct tospovirus species.
Phytopathology, 88(12), 1276-1282.
Nagata, T.; Almeida, A.C.L.; Resende, R. de O.; de Avila, A.C.; (1999) The identification of the vector species of iris yellow spot tospovirus occurring on onion in Brazil.
Plant Disease, 83(4), p 399.
Pozzer, L.; Bezerra, I.C.; Kormelink, R.; Prins, M.; Peters, D.; Resende, R. de O.; de Avila, A.C. (1999) Characterization of a tospovirus isolate of iris yellow spot virus associated with a disease in onion fields, in Brazil.
Plant Disease, 83(4), 345-350.