Phytoplasma diseases of sugarcane.
Sugarcane is severely affected by yellows and decline diseases of phytoplasmal aetiology. These diseases, which are of considerable economic importance, cause similar symptoms but differ in the identity of the associated phytoplasmas, vectorship, and geographic distribution. Sugarcane white leaf (SCWL) and sugarcane grassy shoot (SCGS) occur only in the southeast Asian region and not in other sugarcane growing areas. Both are caused by a single phytoplasma type that is a member of the SCWL group and appears to infect only sugarcane. However, SCWL and SCGS phytoplasmas are closely related organisms and could be differentiated by restriction fragment length polymorphism analysis of rDNA using suitable restriction endonucleases. Sugarcane yellow leaf syndrome (SCYLS) disease has been reported from several African countries, Cuba, and Australia, and is associated with distinctly different phytoplasmas which are not specific pathogens. They include members of the X-disease, faba bean phyllody, aster yellows, SCWL, LfWB, and CirP groups which are known to infect a wide range of wild and cultivated plants and have a low insect vector specificity. Ramu stunt disease of sugarcane (SCRS) is known to occur in Papua New Guinea. This disease is associated with a SCWL-related phytoplasma and is presumed to be naturally spread by the leafhopper Eumetopina flavipes. Sugarcane green grassy shoot (SCGGS) is a newly discovered phytoplasmal disease of sugarcane in Thailand.