Cocksfoot mottle virus spreads to the South Island of New Zealand

In previous surveys of New Zealand cocksfoot (Dactylis glomerata L.) pastures, Cocksfoot mottle virus (CoMV) was detected at only one site near Taupo on the North Island. However, we have recently found CoMV at two sites near Dunedin on the South Island. Isolates from these sites, associated with mild and severe symptoms in cocksfoot (CoMV-Wa and CoMV-Ok, respectively), were partially characterised. In agarose gels, the virions of the two isolates had slightly different mobilities when subjected to an electric field, indicating a difference in net surface charge. However, both isolates produced similar leaf mottle symptoms in wheat, their capsid proteins had similar molecular weights (M-r=ca. 31 kDa) as determined by SDS-polyacrylamide gel electrophoresis and they were serologically indistinguishable in double-diffusion tests using 17 antisera to 10 sobemoviruses. CoMV-Ok and CoMV-Wa were serologically related to Lucerne transient streak virus but not to eight other sobemoviruses. Further surveys using DAS-ELISA showed variable incidences of CoMV (range 0-80%) at nine South Island sites. The beetle vectors of CoMV have not been introduced into New Zealand. At two sites where CoMV was found, we observed severe feeding damage from armyworms (Persectania aversa Walker). However, in growth-cabinet experiments this species failed to transmit the virus. Incidences were significantly higher at mown sites (39%) than at unmown sites (11%), suggesting that mechanical transmission is responsible for spread. In view of the increased use of cocksfoot on New Zealand farms, the impact of CoMV on cocksfoot productivity now needs to be assessed and current levels of resistance to CoMV in commercial cultivars need to be evaluated.