Figure 1. Stunting of wheat (foreground) due to wheat soilborne mosaic. (Photo by Dewey Lienemann)
April 26, 2013
Figure 2. Wheat soilborne mosaic symptoms.
Wheat Soilborne Mosaic in Southeast Nebraska Wheat
Some wheat fields in southeast Nebraska are showing localized or large areas with yellow and stunted wheat. When this condition occurs early in the growing season, it is most likely due to wheat soilborne mosaic (WSBM), a disease caused by wheat soilborne mosaic virus (WSBMV). A wheat sample recently submitted to the Plant and Pest Diagnostic Clinic from Gage County had symptoms of wheat soilborne mosaic. The virus mainly affects winter wheat, but spring wheat also can be infected.
Symptoms And Favorable Environmental Conditions
Stunting caused by wheat soilborne mosaic (Figure 1) can vary from moderate to severe depending on the level of cultivar susceptibility. Leaf symptoms can range from mild green to conspicuous yellow leaf mosaics (Figure 2). Symptoms are most prominent on early spring growth. The disease is favored by wet soils and cool temperatures (a temperature range of 50°F to 68°F with 61°F being optimum). Symptoms wane as temperatures rise in the spring.
Disease Cycle and Spread
The wheat soilborne mosaic virus survives in soil in association with resting spores of the root-infecting fungus Polymyxa graminis. This fungus preferentially inhabits low-lying wet areas. Therefore, field symptoms may be uniform but more often are localized along waterways, low-lying wet areas (Figure 3), or around old building sites. The resting spores of the fungus germinate by forming zoospores which swim in wet soil and infect root hairs, transmitting the virus in the process.
The most damaging infections occur in the fall during cool, wet periods. Following infection, the virus replicates in the roots of resistant and susceptible cultivars, but moves more readily to the leaves of susceptible cultivars. The virus is spread by cultivation, water, wind, and any means by which infested soil is dispersed.
Figure 3. Field symptoms of wheat soilborne mosaic localized in a low-lying area.
Breeding lines and cultivars vary widely in their susceptibility to wheat soilborne mosaic. Yield losses of up to 20% can result from the disease. Rarely, total yield loss can occur in highly susceptible cultivars.
Planting resistant cultivars is the most effective management strategy. Crop rotation is not effective because Polymixa graminis, the virus vector, survives in the soil for many years.
Stephen Wegulo, Extension Plant Pathologist
Randy Pryor, Extension Edcucator
Paul Hay, Extension Educator
Kevin Korus, Extension Educator