Iris yellow spot virus

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symptoms of Iris yellow spot tospovirus on onion (click on image to enlarge it)
Author(s): Howard F. Schwartz, Colorado State University
Source: IPM Images

Iris yellow spot tospovirus (IYSV)

The virus has a world-wide distribution and causes an important disease of onions and other Allium crops. The virus infections reduce the yield and quality of the harvest. Yield losses of up to 50% have been reported. Other plant genera can also become infected, especially ornamentals.

The symptoms start with small elongated leaf lesions which can have different appearances, depending on the cultivar, amount of virus inoculum and environmental conditions. The lesions may be diamond-shaped and straw-coloured or consist of concentric rings of dark and lighter green. Lesions expand, seed heads collapse and infections lead to a general necrosis and early plant death.

Infected onion bulbs can harbor the virus during the winter and cause new infections during the next season. Alternate host plants may also serve as a reservoir for the disease. The virus is transmitted by the onion thrips (Thrips tabaci) in a circulative and propagative manner. Management is based on crop rotation and removing infected plant debris and volunteer plants. The development of resistant cultivars is in progress.

The virus is related to the Tomato spotted wilt virus. Like in that virus, the particles are spherical and have a variable size, ranging from 80-120 nm in diameter. The genome consists of 3 negative sensed RNAs.

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