Natural distribution, spread, and variation, in the tobacco mosaic virus infecting Nicotiana glauca in Australia

SUMMARY Nicotiana glauca is a naturalised introduced species widely distributed in Australia. A survey of stands in the central zone of its recorded distribution has shown that a type of tobacco mosaic virus which characteristically induces a bright yellow mosaic symptom (TMV‐Y) is commonly associated with N. glauca throughout this zone. Surveys of a natural community of N. glauca less than 5 yr old, and in an experimental block, showed that TMV‐Y could spread at a rate, and in a pattern, which could not be explained by contact transmission alone, and which indicated that an airborne vector was probably involved in transmission. These results together have led to the conclusion that the common association of TMV‐Y with N. glauca is due to spread of the virus by an unknown vector(s). Seed transmission of TMV‐Y in N. glauca has not been detected. Molecular hybridisation analysis has shown that all but one of the TMV‐Y isolates studied were related to TMV‐U2, and that the isolate which was unrelated to U2, was partially related to TMV‐U1, TMV‐U5, and tomato mosaic virus. Selected isolates which showed a close relationship to TMV‐U2, also showed a close relationship to TMV‐U5, a distant relationship to TMV‐U1, and tomato mosaic, and very little or no relationship with three other tobamoviruses (sunn‐hemp mosaic virus, odontoglossum ringspot virus, and cucumber virus 4). These results show that the Australian TMV‐Y isolates are similar to the TMV isolated from N. glauca in California.