Choose right onion varieties to avoid viral disease

Are you an onion farmer and you have failed to get good yields from your onion crop due to a strange disease? Research now shows that the seed varieties you have been buying for planting could be susceptible to Iris Yellow Spot virus (IYSV) disease, which is transmitted by thrips.

Farmers should choose the right seed varieties for planting to avoid attracting thrips which carry the disease. IYSV can damage onions and cause great loss of income for onion farmers. Research also shows that onion farmers in Kenya lose up to 75 per cent of their crop but many of the farmers do not know that the onion varieties they choose are responsible for their losses.

Thrips attracted by onion colour and shape

Due to their colour and shape, some onion varieties tend to attract thrips, the major vectors (or carriers) of IYSV that devastates most onion varieties. According to a study conducted by scientists, camouflage and shape of the onion is the first line of defense against the insect-transmitted viral disease.

The Iris Yellow Spot Virus (IYSV) is transmitted by Thrips tabaci, which burrows into the layers of the leaves of the onion plant. The pest saps the from the plant and passes on the virus that causes IYSV.


Symptoms of Iris yellow spot virus on onion include yellow to straw coloured lesions (wounds) on onion leaves and stalks. Dry, elongated lesions or flecks may resemble thrips injury. Lesions may be diamond shaped (this occurs rarely on leaves, more commonly on scapes). Late in the season, infected seed stalks and leaves may fall. Plant vigour and bulb size are also reduced including the onion yield.

Green colour repelled thrips. The green colour of Texas Grano variety leaves also plays a major role in its resistance. This can be explained by the high number of thrips found in Red Pinoy, Red Creole and Green Bunching varieties which have blue-green non-glossy leaves. The Texas Grano and Bombay Red which have green glossy leaves had less number of onion thrips and lower rate of disease incidence.
Therefore, when planning to plant onions, choose your varieties very well.

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