Wheat virus diseases prevalent in Indiana fields
Kiersten Wise, Assistant Professor, Botany & Plant Pathology and Gail Ruhl, Sr. Plant Disease Diagnostician, Purdue University
In recent weeks, there have been concerns about patchy yellowing and stunted areas of wheat across fields in Indiana. Scouting reports, and samples submitted to the Purdue Plant and Pest Diagnostic Lab (PPDL) have confirmed the presence of wheat spindle streak (or yellow) mosaic virus (WSSMV), soil-borne wheat mosaic virus (SBWMV), wheat streak mosaic virus (WSMV), and barley yellow dwarf virus (BYDV-RPV strain) in some of these fields.
Virus diseases of wheat are difficult to tell apart in the field and require lab testing for accurate diagnosis. Infected plants typically first appear in uneven patches of yellow or light green within a field, which can be confused with nitrogen deficiency or winter injury. Often, symptoms appear first in low or poorly-drained areas of the field. With soil-borne mosaic viruses (WSSMV and SBWMV), yellow-green streaks and mottling may be present on leaves and stunting and/or dieback of leaf tips can occur in infected plants (Figures 1, 2, and 3). The level of symptom expression can depend on variety susceptibility. Soilborne wheat mosaic virus can cause a rosette symptom in susceptible varieties, which results in excessive production of severely stunted tillers. We have also observed reddish coloring on lower leaves of wheat plants infected with soilborne viruses (Figure 3). Plants infected with either virus may produce fewer stems and heads, and have reduced kernel number.
Soilborne wheat mosaic and wheat spindle streak mosaic virus infect wheat plants in the fall. Both viruses are transmitted to wheat roots by the soil-borne fungus Polymyxa graminis. This fungus does not cause damage to wheat by itself, but it infects wheat roots and transmits the viruses to wheat plants. Symptoms of virus infection are not apparent until spring, and the severity of symptom expression depends on variety susceptibility and weather. Prolonged cool temperatures in spring (under 60°F) enhance symptom development of both diseases in infected fields. Often, warmer temperatures in spring will help reduce the appearance of symptoms and plants will appear to recover. Yield may not be reduced if the symptoms and distribution of virus within a field are limited, but severe and/or widespread infections can cause stunting and yield loss. Fields that are severely affected at this point in time may need to be replanted. Consult Extension specialists to determine if replanting is needed in a particular location.
Although no control methods are available to reduce symptoms in currently infected plants, it is still important to get an accurate diagnosis for management of future wheat plantings. Crop rotation may not prevent infection since the fungus that transmits the virus can survive in the soil for over 5 years. Therefore, the best way to manage these diseases is to plant resistant varieties in areas with a previous history of the diseases. Varieties are available with good resistance to one or both of the mosaic virus diseases. Be sure to check the variety if you have problems with both soilborne virus diseases in a single field, since some varieties are resistant to only one virus.
The PPDL provides testing for the presence of WSSMV, SBWMV, Wheat streak mosaic virus (WSMV) and 5 strains of Barley yellow dwarf virus (BYDV) with a multiplex PCR detection assay. Contact the PPDL for testing fees. For an accurate diagnosis it is important to dig and submit entire plants exhibiting symptoms (see submission information).
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Figure 1. Wheat exhibiting symptoms of soilborne virus diseases (WSSMV; SBWMV)
Figure 2. Yellow ‘spindles’ on leaves characteristic of soilborne virus disease (WSSMV).
Figure 3. Yellow streaks and mosaic on leaves caused by soilborne viruses (WSSMV; WSBMV)
Figure 4. Plants infected with soilborne viruses (WSSMV; SBWMV) may develop reddish-purple coloring on lower leaves.