SUGAR CANE LEAF YELLOWS: MOLECULAR CHARACTERISATION OF A PHYTOPLASMA ASSOCIATED WITH THE DISEASE IN MAURITIUS

摘要

Two different pathogens, a virus and a phytoplasma have been associated with yellow leaf syndrome (YLS) of sugar cane. The diseases caused by them have been named yellow leaf and leaf yellows, respectively. The phytoplasma was first observed in South Africa in 1998 and thereafter in 2000 in Mauritius where it has been found to be widely distributed in both local and imported varieties. Molecular assays were used to detect and characterise the phytoplasma. A nested-polymerase chain reaction (PCR) approach was found to be reliable for its detection in sugarcane leaves with or without yellow leaf symptoms. The pathogen was present on its own or at times co-existed with the virus of yellow leaf. Considerable variation was observed among strains of the phytoplasma, and two major groups closely related to phytoplasmas associated with stolbur and coconut lethal yellows were distinguished based on their 16S rRNA gene sequences. Both groups were found to be distinct from the strain found in South Africa. This study has demonstrated the importance of leaf yellows associated with YLS in Mauritius and has also enabled characterisation of the causal agent. To date no vector has been associated with disease transmission, and studies are presently underway to investigate this aspect.