Sandal spike

Understanding Sandal Spike

Sandal spike is a complex disease primarily caused by fungal pathogens, although bacterial and insect involvement are also suspected. The disease affects the heartwood of sandalwood trees, leading to internal decay and ultimately reducing the timber's value.

Causative Agents

While the exact etiology is still debated, several fungal species have been implicated in sandalwood spike:

• Fusarium oxysporum f. sp. santali: This is considered a primary pathogen, causing vascular wilt and heartwood decay.
• Phytophthora nicotianae: Contributes to root rot and subsequent heartwood decay.
• Ganoderma lucidum: A basidiomycete fungus that causes root and butt rot, often predisposing trees to sandalwood spike.
• Rhizoctonia solani: Causes damping-off in seedlings and can contribute to root and stem rot in older trees.

Symptoms

The symptoms of sandalwood spike are often subtle in the early stages, making early detection difficult:

• External Symptoms: Initially, there are no visible external symptoms. Later, slight swelling or cracking may appear on the trunk.
• Internal Symptoms: The most prominent symptom is the presence of cavities or hollows within the heartwood. These cavities are often filled with discolored, decayed wood.
• Decline: Affected trees exhibit a gradual decline in vigor, with reduced growth and yellowing of leaves.

Disease Cycle and Transmission

The disease cycle of sandalwood spike is complex and involves several stages:

1. Infection: Fungal spores infect the tree through wounds, root damage, or natural openings.
2. Colonization: The fungus colonizes the heartwood, utilizing the wood's nutrients.
3. Decay: The fungus degrades the heartwood, creating cavities.
4. Spread: Spores are spread through infected wood, soil, water, and potentially by insect vectors.

Transmission occurs through:

• Soil-borne inoculum: Fungal spores persist in the soil and infect roots.
• Contaminated tools: Pruning shears and other tools can spread the fungus.
• Insect vectors: Certain insects may carry fungal spores.
• Root grafts: In dense plantations, root grafts can facilitate the spread of the disease.

Impact of Sandal Spike

Sandal spike has a significant economic impact on sandalwood cultivation:

• Reduced Timber Value: Heartwood decay drastically reduces the commercial value of sandalwood timber.
• Yield Loss: Infected trees may die prematurely, leading to yield losses.
• Plantation Management Costs: Disease management requires costly interventions, such as sanitation and fungicide applications.

Management Strategies

Effective management of sandalwood spike requires an integrated approach:

• Preventive Measures:
  • Healthy Seedlings: Use disease-free seedlings from certified nurseries.
  • Proper Spacing: Maintain adequate spacing between trees to improve air circulation and reduce humidity.
  • Wound Protection: Protect trees from wounds caused by animals, insects, or mechanical damage.
  • Soil Health: Maintain optimal soil health through proper fertilization and irrigation.
• Curative Measures:
  • Sanitation: Remove and destroy infected trees and wood debris.
  • Fungicides: Apply systemic fungicides (e.g., carbendazim, propiconazole) to protect healthy trees.
  • Biocontrol Agents: Explore the use of biocontrol agents, such as *Trichoderma* species, to suppress fungal growth.
  • Resistant Varieties: Research and develop sandalwood varieties with resistance to sandalwood spike.

Recent research focuses on utilizing endophytic fungi to enhance sandalwood resistance to pathogens. Studies are also exploring the potential of using plant extracts with antifungal properties.