A threat to Sandalwood cultivation in Marayoor Sandalwood Reserve through phytoplasma infections

Santalum album, commonly known as Indian Sandalwood is a semi parasitic plant with fragrant wood and is one of the most valuable trees across the globe. The wood and roots contain ‘sandal oil’ which is valued for use in perfumes, incense, cosmetics, soaps, and medicines. The bark contains tannin, which is used for dye production. The states of Karnataka, Tamil Nadu and Kerala are recognized for natural populations of sandalwood contributing 90% of its distribution in India.

Sandalwood Spike Disease (SSD) is the most destructive disease of sandalwood and one of the major cause for decline in sandalwood production. SSD is known to be associated with the presence of aster yellow (‘Candidatus phytoplasma asteris’ 16SrI-B) phytoplasma. Phytoplasma is a group of extremely small bacteria. They don’t have a cell wall and any particular shape. They are bacterial parasites of plants and insects. SSD is identified based on presence of chlorosis, reduction in leaf size, and shortened internodes, causing leaves to become crowded on twigs with a bushy appearance and stems standout stiffly with spike-like appearance.

Researchers collected the symptomatic sandalwood samples from the Marayoor sandalwood reserve in Kerala state and and they confirmed the presence of 16SrI-B phytoplasma, however 16SrXI-B group phytoplasmas were also 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 phytoplasma presence in SSD plants.

(A) A diseased and symptomatic sandalwood branch showing typical little leaf and spike symptoms,
(B) A dead sandalwood plant, due to spike disease

The study reconfirmed the earlier observation of the presence of aster yellows phytoplasmas in plants with SSD disease, but those reports were from Chamundi Hill areas of Karnataka state. There is a great fear of complete loss of sandalwood cultivation from Marayoor Sandalwood Reserve region, which is the only naturalised and largest reservoir in the world. The spread of SSD to the neighbouring sandalwood reserves of Marayoor will cause drastic damage. This study reports the first 16SrXI phytoplasmas detection in plants with SSD disease.

Reference: https://www.indianjournals.com/ijor.aspx?target=ijor:mollicutes&volume=10&issue=1&article=011