Wheat Spindle Streak Mosaic Virus Confirmed
May 1, 2009 Wheat spindle streak mosaic virus (WSSMV), also known as wheat yellow mosaic virus, has been confirmed in wheat samples from Dundy, Red Willow, Richardson, and Saunders counties. WSSMV occurs from mid March to early May.
|Figure 1. Symptoms of wheat spindle streak mosaic virus (WSSMV). (Photo credit: Dr. Robert Bowden, Kansas State University)|
|Figure 2. Symptoms of soilborne wheat mosaic virus.|
WSSMV, like soilborne wheat mosaic virus (SBWMV), is transmitted by the soilborne primitive fungus Polymyxa graminis. Resting spores of the fungus germinate by forming zoospores which swim in water in the soil and infect roots of grasses, transmitting the virus in the process.
Symptoms of WSSMV consist of light green to yellow streaks or dashes that are parallel to the veins and usually are tapered, giving the appearance of spindles (Figure 1). In contrast, symptoms of SBWMV consist of islands of green in yellow (Figure 2). It is difficult to distinguish the two viruses based on symptoms alone; a serological test is needed for confirmation. Both viruses can occur in the same plant at the same time.
WSSMV causes a slight stunting and usually is more uniformly distributed in the field than SBWMV.
Symptoms of WSSMV usually appear before those of SBWMV because WSSMV is favored by cooler temperatures (optimum temperature range for infection: 41-55°F). As day temperatures rise above 64°F, symptoms of WSSMV do not appear on new growth but may persist on older leaves.
Potential Damage and Management
Yield losses caused by WSSMV result from fewer tillers per plant and fewer kernels per head. Infections that occur in the fall cause the most damage; those that occur in the spring cause minimal or negligible damage. In Nebraska, yield losses caused by WSSMV are not known. Losses of up to 64% have been reported in other parts of the United States and the world.
WSSMV is managed by planting resistant or tolerant cultivars and avoiding early planting.
Amy Ziems, Extension Educator
Stephen Wegulo, Extension Plant Pathologist