Detection of Wheat streak mosaic virus in four pasture grass species in Australia

Wheat streak mosaic virus (WSMV) has been recently been identified in Australia (Ellis et al., 2003), where it was detected in glasshouse-grown wheat plants and in a summer wheat crop at the Ginninderra Experimental Station, Canberra. An extensive survey of the area around the wheat crop was conducted to assess the spread of the virus into adjacent pasture species. Samples of grasses were harvested and then tested for WSMV by RT-PCR (French & Robertson, 1994). The survey involved testing c. 1600 samples from a 200 m radius of the infected wheat crop. A number of the grasses sampled showed leaf streaking and mottling characteristic of WSMV in wheat (see Murray et al., 1998 for leaf symptoms in wheat). Using RT-PCR, 14 WSMV-positive samples were found on four common grass weeds of pastures in southern Australia, including African lovegrass (Eragrostis curvula), whorled pigeon grass (Setaria verticillata), spike goosegrass (Eleusine tristachya) and a panic (Panicum sp.). The latter was not identified to the species level, due to the lack of floral structure in the sample. The 271-bp RT-PCR products were sequenced and were over 99% identical to the WSMV isolate from wheat (Ellis et al., 2003). The wheat curl mite (Aceria tosichella), the vector of WSMV (Murray et al., 1998), was also identified on pasture grasses in the sampling area (B. Halliday, personal communication). WSMV is known to have a wide host range amongst the Poaceae (Oldfield & Proeseler, 1996). However, this is the first report of this virus in African lovegrass (Eragrostis curvula) and three spike goosegrass (Eleusine tristachya). These grasses commonly occur within Australian pastures, suggesting that these can act as potential sources of WSMV infection for adjoining cereal crops.