Occurrence of barley yellow dwarf virus and cereal yellow dwarf virus in pasture grasses and spring cereals in Latvia

The relative frequency of three viruses causing barley yellow dwarf disease (BYD) was assessed in spring cereals and pasture grasses at two regions in Latvia in 2000 - 2002. A total of 2589 leaf samples ( 367 from spring oats, 743 from spring barley, 1479 from predominant grass species) were collected from 44 fields of spring oats, 84 fields of spring barley, and 26 pastures. We found that isolates of barley yellow dwarf virus-PAV (BYDV-PAV), barley yellow dwarf virus-MAV (BYDV-MAV) and cereal yellow dwarf virus-RPV (CYDV-RPV) were present in these samples of spring cereals and pasture grasses. The most common isolates of barley yellow dwarf virus were BYDV-PAV and BYDV-MAV in both grasses and cereals, but there was a great difference between years and regions. The proportion of BYD symptomatic cereal samples that reacted positively in TAS-ELISA test was 9 to 15%. The overall BYDV/CYDV incidence in pasture grasses ranged from 2 to 19%. The incidence of BYDV/CYDV infection was higher in Festuca elatior than in other grass species. Isolates of CYDV-RPV were rather rare: only found in Lolium perenne and Dactylis glomerata among six grass species tested and more frequently in barley than oats. This paper reports the first quantitative survey of selected BYD-causing viruses in spring cereals and pasture grasses in Latvia and in the Baltic states. We conclude that three selected virus species are prevalent in spring cereals and pasture grasses in Latvia, although with great variation between years. Further studies are needed to obtain knowledge of the most critical factors that determine these fluctuations.