First report of <i>Wheat streak mosaic virus</i> in Australia

In August 2002, wheat plants in glasshouses at the CSIRO Plant Industry Black Mountain laboratories, Canberra, showed symptoms typical of Wheat streak mosaic virus (WSMV) (Murray et al., 1998). In early 2003, similar symptoms were observed on a summer field experiment at the Ginninderra experimental station, Canberra. The symptoms were characterized by a streaking or mottling of the leaves, leading to chlorosis and in some cases very severe stunting of the plant. In many cases the plants were sterile or produced shriveled seed. Affected plants sometimes showed a curling of the leaf; a symptom caused by the wheat curl mite (Aceria tosichella), the vector of WSMV (B. Halliday, 2003, CSIRO Entomology, ACT 2601, Australia, personal communication). RT-PCR tests were used to confirm the presence of WSMV according to the methods of French & Robertson (1994). Following agarose gel electrophoresis, a band of the expected size (271 bp) was amplified from diseased wheat, but not from healthy wheat or a barley control. The sequence of the RT-PCR product was compared with other WSMV sequences in the GenBank database and was found to have over 95% homology. Additional confirmation was obtained by ELISA using a kit for the detection of WSMV (Agdia Inc., Elkhart, IN, USA). Diseased plant samples gave a positive reaction, while that of the healthy wheat control was negative. These results provide the first evidence of WSMV in Australia. Since the discovery of WSMV in Canberra, the virus has been identified in other states, suggesting that it arrived in Australia some years ago, but had remained undetected.