University of Illinois

No. 3/April 11, 1997

Soilborne Mosaic of Wheat

With the return of cooler weather this week, soilborne mosaic virus symptoms on wheat should be more noticeable. This pathogen is usually associated with cool, wet conditions in either fall or spring. In Illinois, it is much more commonly seen in early spring throughout the southern and central parts of the state. Fortunately, it rarely causes economic loss but can cause concern due to the yellowing or reddening of infected plants.

Soilborne mosaic virus (SMV) is unusual in that it is vectored, or carried, by a fungus known as Polymyxa graminis. This fungus is found in low-lying areas of fields and prefers a wet habitat. Soils do not have to be saturated to promote this fungus, but only moderately wet. Disease distribution tends to be associated with these low areas, but some fields may show almost uniform yellowing or mottling of wheat leaves. Symptoms can vary greatly depending on the wheat variety, soil moisture levels, virus strain, and general health of the crop.

Symptoms of SMV range from mild mottling of leaves to severe yellowing. Stunting also can be seen in severe cases, and rosetting can occur in highly susceptible varieties. Rosetted plants fail to set tillers and remain as stunted leafy clumps. As new leaves unfold, they develop parallel streaks or dashes and appear mottled. Warming spring temperatures slow symptom development and eventually stop the disease process. Symptoms are normally confined to lower leaves.

Control measures include selection of resistant or tolerant wheat varieties where available. Other controls include crop rotation and late autumn seeding (after the fly-free date).

H. Walker Kirby, Department of Crop Sciences, (217)333-4424