Context: The threat to sandalwood is increasing as the deadly sandalwood spike disease (SSD) has started spreading to private fields where the cultivation of this aromatic tree has been taken up on a commercial basis.

Key Points

• A study has now shown that this ‘invisible’ disease, which is wiping out the sandalwood trees, can transmit through seeds of infected trees through the presence of disease-causing bacteria called Phytoplasma.

• The disease was first reported from Coorg distinct of Karnataka State in 1903.

• The disease is one of the most destructive diseases of Sandal tree – an economically important tree and is prevalent in the areas wherever Sandal trees are grown.

• Significantly the disease is confined to India and Indonesia.

• In India, Sandal tree to common in Southern States including Karnataka, Kerala and Tamil Nadu.

Symptoms of Sandal Spike Disease

• The common symptom called the ‘rosette spike’ is characterised by severe reduction in leaf size and reduction of internodes.

• This results in crowding of leaves on leaf bearing branches.

• The new leaves are further reduced in size.

• Such leaves become stiff and stand out as spikes.

• In advanced stages of the disease, the leaves become reddish or yellowish.

• This symptom appears just before death of the tree.

• The flowers of the infected trees become leaf like and the infected plants do not bear any fruits, the ends of roots of infected plants die out resulting in the loss of the haustorial connection with the host plants.

• Ultimately the infected plants dries up and die.

• The other symptom called ‘pendulous spike’ is due to continuous apical growth of individual shoots without proper thickening and results in drooping of shoots.

• The dormant buds do not grow and no rosettes are produced.

• In this symptom, the roots and haustorial connection are not damaged.

• MLO (Mycoplasma like organisms) is the causal organism.

• The MLO is reported to infect a large number of plant species such as Eucalyptus grandis, Vinca rosea, Zizyphus oenoplea, Dodonea viscosa.

• The disease is transmitted through root contacts and insect vectors.

Control Measures of Sandal Spike Disease

• No specific method to control the disease has so far been developed.

• However, it is claimed that planting of Mysore gum trees (ahybriod of Eucalyptus tereticornis) at a distance of 10-20 metres from the Sandal trees keeps the latter free of infection.

• As with other mycoplasmal diseases, treatment with tetracycline checks the disease.

• Attempts are also being made to develop disease resistant trees via genetic engineering and tissue culture technique.