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Government Of Assam Handloom Textiles & Sericulture Directorate of Sericulture

Food Plants of Silkworm

Cultivation of Som and Soalu

  1. Generally Som is used for rearing of muga silkworm in upper Assam, while Soalu is used in lower Assam. Som tree is more prevalent in upper Assam and produces reeling cocoon whereas Soalu is more common in lower Assam and produces seed cocoon.
  2. Propagation of the host plants and their management: The host plants of muga silkworms are available in nature. The plants are propagated in two ways (i) Sexual method and (ii) Asexual method. Som and Soalu plants are propagated through mainly seeds. Seeds are usually propagated by fallen excreta of birds with undigested seed scattered over a wide area. Seeds from selected plants ensure production of healthy seedlings.
  3. Propagation of Som: Som can be propagated both sexual and asexual methods.
  4. Sexual Propagation: Sexual propagation is through seedlings, particularly the seed propagation carries a varied population, this to utilize in selection and hybridization. For seed germination certain pre-requisites are needed to be fulfilled such as selection of quality seed, preparation of land, and the seed should be selected such that can definitely germinate. This is possible only when the seed is subjected to suitable environmental conditions, embryo of seed is alive, and healthy, in internal conditions of seed are favourable for germination.
  5. The fresh seeds will have greater germination rate than the stored once. Seeds must be washed with fresh water until the flesh of fruit is withdrawn and dried well, however minimum moisture percentage should be maintained, i.e. at least 6 %. Sowing of seeds may be by way of broadcasting or sowing in lines.

Propagation through seeds:

Propagation through seeds is one of the cheapest and easiest methods.


Som being a cross pollinated plant, sexual propagation introduces variability in the progeny and gives scope for selection of new varieties. It is suitable for large scale multiplication to build up stocks for preparation of grafts.


Comparatively long gestation period to provide leaves for silkworm rearing. The desirable traits of improved cultivars cannot be perpetuated.

Source and time of collection of seeds

Seeds of Som become mature in April to June in Assam and other N.E. states. Collect mature seeds from the plants during April and May in lower Assam and May and June in upper Assam and other N.E. states.


  1. Collect seeds only from fully ripened fruits.
  2. Do not damage seeds during extraction.

Viability of Som seed: There is no dormancy in Som seeds. Freshly harvested seeds have highest germinability. Seed is viable up to 10-20 days after harvesting of seed. The lose viability with the passage of time. The viability of Som seeds loses if preserved for a long period. Viability decreases after 20 days of storage till 45 days.

Selection of viable seeds: The seed quality can be selected by floatation test. Selection of healthy and viable seeds is done by floating the seeds in water. The healthy seeds sink and shriveled and unfertilized seeds float. The pulp of the seeds is washed off by kneading two or three times in running water and dried under shade for a few hours.

Storage of seed: The seeds may, however, be stored in moist seed beds for six to eight weeks under low temperature to prolong their viability. 10°C is the storage temperature of Som seed. It is desirable to predict the quality of the seeds in respect of germination capacity.

Raising of Som seedlings: Som seedlings can be raised by sowing seed in soil directly or in polytubes.

Pre treatment of seeds and Seed dressing:

  1. 1. Prior to sowing, soak the seeds for 20-24 hours in water and treat the seeds with Bavistin or Carbendazim @ 2 g/kg seed.
  2. 2. For seed dressing Trichoderma pseudomonas @ 20 g/kg seed has been suggested in place of Bavistin.

Preparation of nursery Bed or Seed bed: Nursery can be prepared after monsoon from mature seed. Seedlings are available in plenty in a plantation before monsoon. Though seeds can be directly used for raising plantation, the present trend is it grow seedlings in the nursery and transplant them in the field to reduce the period of establishment and save wastage of precious seed material.

Layout of bed / Bed size

  1. Select well drained high land in a shady place. The soil is dug or ploughed twice or thrice up to 30 cm depth, followed by leveling properly. Apply 6 cft FYM and mix thoroughly with the soil.
  2. Seed beds of convenient size are prepared. Make 2 x 1 m beds and elevate the same up to 15 cm - 20 cm.

Seed sowing: Seeds are sown in lines in the prepared beds at a spacing of 15 cm in the row and 15 cm between rows at a depth of about 2-4 cm. Sow 2 kg seeds (approx.)/bed

Germination of Seed:Germination starts after 30-45 days of sowing. Germination of Som is 82% (average). Normally one seed gives rise to one seedling only but polyembryonate seedlings are also known to occur. In the polyembryonate seedlings, twins and triplets have been observed in Som which are rare occurrences. The frequencies of twins and triplets are 4.5% and 0.6% respectively. The twins and triplets after separation are capable of developing into independent plants.

Transplantation of seedlings to poly tubes:

  1. The seedlings can also be raised in polythene tubes. Seedling of 6 months, 10-20 cm (3” to 4”) height is collected for preparation of nursery. The seeds after collection are kept on moist bed under tree shade covered with moist gunny bags followed by sprinkling of water to maintain the moisture. The germination starts after four weeks. The germinated seeds are sorted out every day and sown individually in polythene tubes of 9 x 6 inch size of 150-220 guaze, filled with rooting media and kept under tree shade.
  2. Rooting media
  3. A mixture of soil, sand and farm yard manure (FYM) in the ratio of 1:1:1 soil: sand: FYM is used as the rooting media for raising seedlings in the polythene tubes figure.
  4. Seedling survivability: 70-85(%)

Gap filling: Gap fills on the 10th day of sowing of seed on seed bed. Gap filling of seedling polytubes