Sandal spike disease

Sandal spike disease is the most devastating pathology affecting the white sandalwood tree (Santalum album). Classified as a phytoplasma disease, it severely disrupts the plant's vascular system, specifically the phloem, causing systemic physiological decline and eventual death of the host tree within a relatively short period.

The disease is caused by phytoplasmas, which are specialized wall-less bacteria that inhabit the plant's sieve tubes. These pathogens are transmitted by sap-sucking insects, primarily leafhoppers, which acquire the phytoplasma while feeding on an infected host and subsequently introduce it into healthy trees during the feeding process.

The primary host for this disease is the sandalwood tree, which is economically significant for its aromatic heartwood and oil content. The disease is highly contagious and spreads rapidly within plantations, not only through insect vectors but also via root grafts, where the pathogen moves from the root system of an infected tree to an adjacent healthy neighbor.

The most distinctive symptom of the disease is the extreme reduction in leaf size, which causes the foliage to become thin, stiff, and pointed, resembling spikes. This is accompanied by shortened internodes, leading to a crowded, rosette-like appearance of leaves. Infected trees eventually show signs of yellowing (chlorosis), dieback of branches, and a complete cessation of metabolic activities, leading to the death of the tree.

There is currently no cure for Sandal spike, making rigorous management essential for the survival of plantations. Control strategies include:

• Early detection and immediate rogueing (removal) of infected trees.
• Destruction of removed plant material to eliminate sources of the pathogen.
• Management of insect vector populations using appropriate insecticides.
• Maintaining proper spacing between trees to prevent the spread via root grafting.

Integrated pest management and continued research into resistant genotypes of sandalwood remain the most promising avenues for mitigating the impact of this disease on the industry. Long-term forest health requires continuous monitoring and strict adherence to sanitary protocols to prevent further dissemination of the phytoplasma.