Sandalwood

Santalum album. Linn commonly known as East Indian sandalwood or chandan belongs to the family Santalaceae. It is highly valuable and becoming endangered species. It is distributed all over the country and more than 90% lies in Karnataka and Tamil Nadu covering 8300 sq kms.  Sandalwood plays an important role in the religious life of Indians. The essential oil obtained from this wood has occupied significant place in perfumery industries/market. Although it is available in some other countries still the Indian Sandalwood has retained its dominance over other sources because of its quality.

Habitat

Santalum album occurs from coastal dry forests up to 700 m elevation. It normally grows in sandy or stony red soils, but a wide range of soil types are inhabited. This habitat has a temperature range from 0° C to 38° C and annual rainfall between 500 and 3000 mm.

Seed technology

Santalum album is an evergreen tree. It can grow to a height of 20 m and attain a girth of over 1.5 m. It flowers and fruits twice a year during March-April and September-October. Trees start flowering from 3 years of age. Seed production generally is good in one of the seasons. Certain trees flower only once a year and some do not flower regularly. About 6000 seeds make 1 kg. Seeds can be collected directly from the tree.

Seed Collection: Santalum album fruits are collected fresh from more than 20 years old trees and are soaked in water and rubbed to remove the soft pulp; then it will be dried.

Seed Storage: Seeds are naked, lack testa and are dried and stored in polybags or gunny bags.

Pretreatment: Acid scarification with concentrated H₂SO₄ for 30 minutes with string and washing in running water, or soak the seeds in 0.05% gibberellic acid overnight.

Nursery technology

Two types of seed beds are used to raise sandal seedlings: sunken and raised beds. Both of them perform equally well under different climatic conditions.

Seed beds are formed with only sand and red earth in the ratio 3:1 and are thoroughly mixed with nematicides (Ekalux or Thimet at 500 g per bed of 10 m x 1 m). Around 2.5 kg seed is spread uniformly over the bed, covered with straw which should be removed when the leaves start appearing on the seedlings. Sandal suffers from a very virulent disease caused by combined fungal and nematode infection. The initial symptom is that of wilting of leaves followed by suddan chlorosis and root decay. On account of this the mortality rate is very high, which can be controlled by the application of nematicide (Ekalux) and fungicide (Dithane). Seeds beds are to be sprayed with fungicide Dithane Z-78 (0.25%) once in 15 days to avoid fungal attack and 0.02% Ekalux solution once in a month to avoid nematode attack.

When seedlings have reached 4 to 6 leaf stage they are transplanted to polybags along with a seed of Cajanus cajan, Alternanthera sessilis (L.) R. Br. ex. Dc, Cassia fistula L., Mimosa pudica L., etc., the primary host for better growth of sandal. Seedlings are carefully removed from beds with all roots intact; roots should not be allowed to dry. Shade can be provided for a week immediately after transplantation. Watering is to be done once a day, but excess moisture is to be avoided. Host plants are to be pruned frequently, so that they do not over grow sandal and hamper its growth. Polybags should contain soil mixture of ration 2:1:1 (Sand: Red earth: Farmyard manure). It has been found that polybags of 30 x 14 cm size are the best. To avoid nematode attack Ekalux of 2 gm/polybag or 200 gm for 1m³ of polybag mixture should be thoroughly mixed before filling the bags. Shifting may be done once in two months to avoid root penetrating soil and grading is to be done once in three months. Weeding is to be done at regular intervals.

Plantable seedlings of about 30 cm height can be raised in 6-8 month’s time. A well branched seedling with a brown stem is ideal for planting in the field.

Plantation

Regeneration has been obtained successfully by following methods.

• Dibbling of seeds into bushes
• Dibbling of seeds in pits or mounds
• Planting container raised seedlings in the nurseries

Dibbling of Seeds into Bushes

This methods is adopted in open scrub jungles with lot of bushes. Seeds are sown during monsoon. An instrument can be made using a bamboo pole of 4 to 6 cm internal diameter and a length of 1.5 m for the purpose of sowing seeds. The septa at the nodes are removed and one end of the pole is sharpened or a hollow metal piece is attached. The pole is introduced at the base of the bush and through the hole 4 to 5 seeds are transferred to the base of the bush. Fairly good success has been achieved by this method.

Dibbling of Seeds in Pits or Mounds

The usual trench mound technique adopted in forest for other species is also adopted for sandal. But here a perennial host plant is also grown along with sandal either on the mound or in the pit.

Planting Container Raised Seedlings in the Nurseries

Pits of 50 cm³ are dug out at an espacement of 4 m x 4 m. Healthy sandal seedlings; preferably above 30 cm in height are planted in the pits. Miscellaneous secondary forest species as host plants are planted in the same pit or they may be planted in separate pits in a quincunx pattern. This method has proved successful in many forest areas. At the time of planting in the field a perennial host, if given, increases the growth of sandal, otherwise it shows stunted growth with pale yellow leaves and ultimately dies in about one year. Sandal has over 150 host plants, some of the good hosts being Casuarina equisetifolia, Acacia nilotica, Pongamia pinnata, Melia dubia, Wrightia tinctoria and Cassia siamea.

Heartwood Formation and Oil Content

Heartwood formation in sandal trees generally starts around 10-13 years of age, but what triggers this process has not been very well understood. Certain factors, generally relating to stress, such as gravelly dry soil, insolation, and range of elevation (500-700 m), seem to provide the right environment for the formation of heartwood, irrespective of the size of the stem after 10 years of age. The occurrence of heartwood varies. The value of heartwood is due to its oil content, and the superiority of the oil is due to the percentage of santalol.

• In a tree the oil content is highest in the root, next highest in the stem at ground level, and gradually tapers off towards the tip of the stem.
• Similarly, there is a gradient in oil content from the core to the periphery of the heartwood in a stem.

• Young trees (height less than 10 m, girth less than 50 cm, and heartwood diameter 0.5-2 cm) have heartwood with 0.2-2 percent oil content, which has 85 percent santalol, 5 percent acetate, and 5 percent santalenes.
• Mature trees (height 15-20 m, girth 0.5-1 m, and heartwood diameter 10-20 cm) have heartwood with oil content of 2- 6.2 percent, which has over 90 percent santalol, 3-5 percent acetate, and 3 percent santalenes.

Pest and Disease

Spike disease is one of the important diseases of sandal. This disease is caused by mycoplasma-like organisms (MLO). It can occur at any stage of development of the tree. As the disease progresses, the new leaves become smaller, narrower or more pointed and fewer in number with each successive year until the new shoots give an appearance of fine spike. At the advance stage of disease the inter nodal distance on twigs becomes small, haustorial connection between the host and sandal breaks and the plant dies in about 2 to 3 years.

Spread of disease is sporadic and the disease is transmitted in nature by insect vectors. It has been found that other insect vectors in addition to Nephotettix virescens may also be responsible for transmission of disease. So far no permanent remedial measures have been prescribed for control of spike disease.

Stem borers Zeuzera coffease Nietn (red borer) Indarbela quardinotata Walker (bark-feeding caterpillar) and Aristobia octofasiculata Aurivillius (heartwood borer) are some of the pests causing considerable damage to living trees.

Source : Sandalwood Information System. Institute of Wood Science and Technology, Bengaluru