Source: Plant Disease [edited]
[ref: Braithwaite KS, Tom L, Kuniata LS. Planthopper transmission of Ramu stunt virus, a _Tenuivirus_ causing the sugarcane disease Ramu stunt, and its distribution in Papua New Guinea. Plant Disease 103, First Look. doi: 10.1094/PDIS-01-19-0058-RE]
Ramu stunt is a serious disease of sugarcane, currently reported only from Papua New Guinea (PNG). It is found in both commercial sugarcane grown on the Ramu Agri Industries Limited (RAIL) estate, and in chewing canes (_Saccharum officinarum_) grown in village gardens across the country.
The vector of Ramu stunt disease is the island sugarcane planthopper, _Eumetopina flavipes_. Here we report on the successful transmission of Ramu stunt using _E. flavipes_ and verify that the disease is caused by Ramu stunt virus (RmSV), a virus with homology to the genus _Tenuivirus_. Diagnostic RT-PCR screening, with partial genome sequencing and viral protein characterisation, was used for confirmation.
Disease surveys were undertaken on the RAIL estate, along roadsides and in village gardens in parts of PNG, and 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 found to be less common than was predicted during early surveys based on symptoms alone, and genotypic variation was associated with geographic location.
[Ramu stunt is one of the most economically damaging diseases of sugar cane in Asia. The complete genomic sequence of a tenuivirus suspected to be associated with Ramu stunt was determined in 2016 by next generation sequencing of total RNA from Ramu stunt infected sugar cane (doi: 10.1007/s11262-015-1279-5, see link below). The name Ramu stunt virus was proposed for a potential new virus, but proof of causality for the disease has only now been supplied by the work described above, by transmitting viable virus using a specific vector to a healthy host to induce the same disease symptoms as in the infected source plant (modified Koch's postulates).
All currently known tenuiviruses have hosts in the family Gramineae which includes cereal crops like rice (_Rice grassy stunt virus_, _Rice stripe virus_, _Rice hoja blanca virus_), maize (_Maize stripe virus_) and wheat (_Iranian wheat stripe virus_). Each species in the genus is transmitted by a particular species of planthopper in a circulative, propagative manner. Infected hoppers remain infectious for life and can be transported on air currents to spread the viruses quickly over long distances. High vector populations are often associated with virus outbreaks. Hoppers may also be pests in their own right, damaging above ground parts of the host and leaving small injuries exposing the plant to fungal and bacterial infections.
Disease management for these viruses includes cultural practices (such as crop rotation or fallow periods), vector control, removal of virus and vector reservoir hosts and use of crop cultivars with reduced sensitivity or resistance to the virus, the vector, or both. Hopper adaptation overcoming plant resistance has been a problem, for example for rice-infecting tenuiviruses. The application of insecticides to migratory hoppers is being used in some areas to reduce disease incidence.
Ramu stunt is not to be confused with sugar cane ratoon stunting disease (RSD) which is caused by the bacterium _Leifsonia xyli_ s.sp. _xyli_ which was also reported from the Ramu Valley in PNG in 2008 (ProMED-mail post 20080114.0175).
Papua New Guinea:
http://www.nationsonline.org/maps/papua_map.jpg (with provinces)
Ramu stunt symptoms on sugar cane:
_E. flavipes_ vector:
Information on Ramu stunt virus:
https://link.springer.com/article/10.1007%2Fs11262-015-1279-5 (sequence determination)
Ramu stunt disease:
Information on genus _Tenuivirus_:
Virus taxonomy via:
Information on planthopper vectors via: