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Ramu stunt is a serious disease of sugarcane, currently only reported from Papua New Guinea. It is found in both commercial sugarcane grown on the Ramu Agri Industries Limited (RAIL) estate and in chewing canes ( Saccharum officinarum L.) grown in village gardens. The vector of Ramu stunt disease is the island sugarcane planthopper, Eumetopina flavipes Muir. Here we report on the successful transmission of Ramu stunt using E. flavipes and verify that the disease is caused by Ramu stunt virus, a virus with homology to the genus Tenuivirus . Diagnostic reverse transcription PCR screening, with partial genome sequencing and viral protein characterization, was used for confirmation. Disease surveys were undertaken on the RAIL estate, along roadsides, and in village gardens in parts of Papua New Guinea. When the disease was identified, partial genome sequencing of the virus was performed to assess the extent of genome variability among isolates. The disease was less common than predicted from early surveys based on symptoms alone, and genotypic variation was associated with geographic location.

The island sugarcane planthopper, Eumetopina flavipes Muir, is the only known vector for Ramu stunt disease of sugarcane. This study examined the relationship between host plant distribution and abundance, and E. flavipes distribution, abundance and levels of population connectivity in Papua New Guinea (PNG), the Torres Strait (TS) and northern peninsula area (NPA) of Australia, as a first step in establishing E. flavipes invasion potential through the TS/NPA. Results show that E. flavipes utilises a wide range of Saccharum host species in PNG and that the occupation rates and abundances differed significantly among host types. For hosts in common, the proportion of plants occupied in PNG was significantly greater than in TS/NPA. This is likely the result of greater overall host density and connectivity in PNG. E. flavipes abundance per plant did not differ significantly between the two regions suggesting a possible plant-specific abundance and/or dispersal threshold independent of location. Whilst E. flavipes presence and persistence was highly variable at some TS/NPA locations, large and stable infestations occurred down the western edge of the TS archipelago. These populations appear to link PNG to the NPA and offer a potential incursion route for Ramu stunt disease. The stability of these populations appears to be associated with the availability and persistence of host material, which in turn is significantly affected by variation in cultivation practices. In the TS/NPA, implementation of pre-emptive management of E. flavipes via cultivation techniques, such as simultaneous tip-pruning, may be an effective means of control for the pest, and would be simpler and preferable to the direct management of Ramu stunt disease should it be detected in the TS/NPA.

Fiji leaf gall is an important disease of sugarcane in Australia and other Asia-Pacific countries. The causative agent is the reovirus Fiji disease virus (FDV). Previous reports indicate that there is variation in pathology between virus isolates. To investigate the amount of genetic variation found in FDV, 25 field isolates from Australia, Papua New Guinea and Malaysia were analysed by partial sequencing of genome segments S3 and S9. There was up to 15% divergence in the nucleotide sequence among the 25 isolates. A similar amount of divergence and pattern of relationships was found for each of the two genomic segments for most of the field isolates, although reassortment of genome segments seems likely for at least one of the Papua New Guinean isolates. The finding of a high level of variation in FDV isolated in different regions has implications for quarantine and disease management.