A threat to sandalwood cultivation in the naturalised Marayoors andalwood reserve (Kerala, India) through single and mixed phytoplasma infections

The forest of Southern India, especially in the states of Karnataka, Tamil Nadu and Kerala are recognised for natural populations of sandalwood contributing 90% of its distribution in India. The sandal spike disease (SSD) of sandalwood is known to be associated with the presence of aster yellows (‘Candidatus Phytoplasma asteris’, 16SrI-B). The recent survey and collection of the symptomatic sandalwood samples from the Marayoor sandalwood reserve of Kerala state confirmed the presence of this phytoplasma; however, also 16SrXI-B phytoplasmas were identified. These phytoplasmas were present in single or in mixed infection in the collected sandalwood, sugarcane and Indian gooseberry samples from this area. This study is the first report of 16SrXI-B phytoplasmas in sugarcane in Kerala of witches’ broom disease in Indian gooseberry associated with aster yellows phytoplasmas and the first report of 16SrXI-B phytoplasma presence in SSD plants. These findings unveil serious threat to existing sandalwood and sugarcane cultivation in the Marayoor sandalwood reserve area, and demand a thorough investigation on phytoplasma insect vectors to efficiently manage these diseases associated with phytoplasmas.