Cultivation of Som and Soalu
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.
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.
Propagation of Som
Som can be propagated both sexual and asexual methods.
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.
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 Seeds must be washed with fresh water until the flesh of fruit is withdrawn and dried well, however minimum moisture percentage should be maintained, i.e. at least 6 %.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.
Merits
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.
Demerits
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.
Precautions
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
Raising of Som seedlings
Pre treatment of seeds and Seed dressing
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
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
Gap filling
Gap fills on the 10th day of sowing of seed on seed bed. Gap filling of seedling polytubes