RAMU STUNT: RESISTANCE SCREENING AND VALIDATION OF THE DIAGNOSTIC TEST

RAMU STUNT IS a major disease of sugarcane in Papua New Guinea and was first recognised at Ramu Sugar (Ramu Agri-Industries Limited) in 1985 when it caused a serious epidemic. The disease is a major quarantine disease risk to the Australian sugar industry. Resistance screening trials have been conducted at Ramu in the past, but there is little information on the latest smut resistant varieties which comprise the current Australian crop. To address this gap, a screening trial was planted in late 2010. The trial relies on the insect vector, Eumetopina flavipes, to spread the disease into the test canes from spreader rows of the highly susceptible variety Ragnar. Disease levels and Eumetopina numbers have been monitored since April 2011 and this will continue through to the ratoon crop. At the time of the epidemic the causal agent was unknown, but research carried out since indicates that it is a virus. A diagnostic test that detects viral RNA has previously been developed, but has not been widely tested in a field situation at Ramu. The screening trial presents an opportunity to validate the diagnostic test. The standard varieties in the trial have known disease ratings. Leaf samples, both with and without symptoms of Ramu stunt, have been screened with the diagnostic test, allowing symptoms, disease rating and diagnostic result to be correlated. The test, once validated and operational, will help Ramu Agri-Industries monitor the disease, help the Australian sugar industry prevent or manage any potential incursions and allow safer movement of sugarcane germplasm around the world.