Winter wheat samples (displaying yellow dwarf symptoms) submitted to the Pest Diagnostic Clinic (U of Guelph) has confirmed the presence of Barley Yellow Dwarf Virus (BYDV-PAV strain) and Cereal Yellow Dwarf Virus (CYDV-RPV strain). Both of these various are very common in Ontario and until recently were grouped as different strains of BYDV. What was once described as BYDV-RPV has been reclassified and put into the cereal yellow dwarf virus group and is now referred to as CYDV-RPV.

Although BYDV-PAV and CYDV-RPV strains are very difficult to distinguish based on visual symptoms there are however some subtle differences. The majority of the BYDV-PAV samples had typical late season symptoms - yellow or red upper leaves (especially the flag) with brown/dead tips (Figure 1). Yellow stunted plants were positive for CYDV-RPV. Many of the samples however had a combination of these symptoms and as expected (thankfully!) they had both viruses present.

The impact on yield for BYDV-PAV infected plants can be serious but most likely will be low (5-10%) in most fields but some fields may be higher if other problems exist. The CYDV-RPV strain virus is often more damaging then BYDV-PAV and based on the field symptoms this year, yield losses will be higher since many of the plants are severely stunted and are prematurely dieing.

How about resistance genes?

Although resistance genes are being incorporated into wheat varieties but it has been slow and will take some more time.

Figure 1. BYDV - PAV strain on wheat. Note yellow colour and red tip (Tenuta, OMAFRA, 2007)