White leaf and grassy shoot diseases of sugarcane

Sugarcane white leaf (SCWL) and sugarcane grassy shoot (SCGS) are lethal phytoplasmal diseases of sugarcane (Saccharum spp. and hybrids) which are known to occur only in south-east Asia. They are caused by SCWL and SCGS phytoplasmas, respectively. These prokaryotes are closely related phylogenetically and are members of the rice yellow dwarf (RYD) phytoplasma group or 16SrXI group. However, they can be differentiated from each other and from the most closely related phytoplasmas by restriction fragment length polymorphism (RFLP) analysis of polymerase chain reaction (PCR)-amplified rDNA using suitable restriction endonucleases. Molecular diagnosis of SCWL and SCGS infections in plant and insect hosts has been based on serological assays and nucleic acid-based methods such as dot and Southern blot hybridization and PCR technology. Currently, the powerful PCR technology using primers amplifying phytoplasmal rDNA sequences is the most widely employed and has nearly completely replaced the other techniques. Like other phytoplasmal diseases, SCWL and SCGS are difficult to control. Chemotherapy of diseased cuttings and chemical control of the vectors have proven impractical and difficult. The use of resistent clones is also limited. Thermotherapy including hot-water and hot-air treatments of diseased cuttings may reduce pathogen inoculum. At present, use of healthy plant material, roguing of diseased plants, avoidance of ratooning, and for SCWL only, adjusting of planting time, are important measures for reducing the incidence of the diseases