First report of Iris yellow spot virus on onion in Germany
The NPPO of Germany recently informed the EPPO secretariat of the first detection of Iris yellow spot virus (Tospovirus, IYSV – EPPO Alert List) in Rheinland-Pfalz on onions (Allium cepa and Allium fistulosum). In Rheinland-Pfalz, symptoms resembling those of IYSV had already been observed in 2003 on onion crops. In summer 2007, as typical symptoms of IYSV were observed again in the same onion-growing area, a survey was initiated and 25 sites were visually inspected. As a result, 9 symptomatic lots were tested in the laboratory (using DAS-ELISA) and found to be infected by ISYV. In the field, infected onion plants often showed white to straw-coloured oval, necrotic lesions on the leaves. At a later stage of the disease, the number of lesions increased and led to decay of the leaves. These symptoms could be confused with those caused by Thrips infestations, hailstorms, herbicide phytotoxicity, or early infections by various fungal diseases. While at the beginning of the vegetation period, only isolated plants or small groups of plants appeared to be infected, onion plots were evenly infected at a later stage. So far, yield reduction could not be quantified but was considered moderate. Because Thrips tabaci is thought to be the main vector of the disease, insecticide treatments were applied to control thrips populations.
The pest status of Iris yellow spot virus in Germany is officially declared as follows: Transient, in one area; under eradication
Sources
NPPO of Germany, 2008-02.