Grassy shoot: The destructive disease of sugarcane

Abstract

Sugarcane is one of the important commercial cash crops grown widely for sugar production. Red rot, smut, wilt, grassy shoot and yellow leaf are the major diseases of sugarcane worldwide; however the sugarcane grassy shoot (SCGS) is considered the most destructive one due to the associated total loss of millable canes production. Although the crop is cultivated in tropical and sub-tropical regions across the globe, widespread occurrence of the disease is mostly reported only from South and South East Asian countries. The disease was first reported in India in 1949. Based on its symptomatology, it is known as grassy shoot in India, Pakistan, and white leaf in Thailand, Vietnam, Myanmar, China and known by both names in Sri Lanka. The past seven decades witnessed several research advancements in symptomatology recognition, diagnosis and management of this disease. The nested PCR based diagnostic approach initiatives taken during 1990s followed by the in silico virtual RFLP analyses development in the period of 2007–2009 revolutionized the molecular characterization of the pathogen based on the variability analyses which resulted in the description of reports of many phytoplasma strains infecting sugarcane. Several phloem sap feeding leafhoppers such as Deltocephalus vulgaris, Cofana unimaculata, Exitianus indicus and Maiestas portica in India, Matsumuratettix hiroglyphicus and Yamatotettix flavovittatus in Thailand and D. menoni in Sri Lanka were reported as insect vectors during the last ten years. The recent use of next generation sequencing technologies helped to sequence whole genome of the SCGS phytoplasma. Currently, heat therapy and pathogen elimination through meristem tissue culture based seedling production are the only available management techniques to prevent the disease spread into new areas. Despite the fast pace of research in pathogen detection and genomics, the research on disease management under field conditions still remain grey and pose challenges to sugarcane pathologists.