INDIAN SERICULTURE AN OPTIMIST’S REVIEW- Dr. TP. Mohandas

Dr. T. P. Mohandas is a senior Scientist with Central Silk Board (CSB) India. He was born in Thrissur district of Kerala in 1962. After obtaining PhD in zoology from University of Calicut in 1993, he joined the Central Silk Board in 1996 as a Senior Research Officer where he rendered 15 years of fruitful service in various capacities. An entomologist by training, Dr. Mohandas has amply demonstrated his abilities as a silkworm molecular biologist during his tenure at the Seri biotech Laboratory of CSB in Bangalore. His work spans across the disciplines of Molecular breeding, Molecular genetics, Pest management, silkworm seed production & sericulture extension and his grasp of the subject, the seriousness of approach and depth of analysis are demonstrated by his publications in reputed journals such as Genome, Genetica, European Journal of Entomology etc. He is widely read and is a person with diverse interests and a most refined mind. Apart from his interest in biological sciences Dr. Mohandas loves music, literature and fine arts. He has a fine tuned ear especially to Indian classical music. As a person he is kind hearted and generous, sporting positive thoughts and always radiating enthusiasm and energy. In this article Dr. Mohandas gives us an overview of Indian sericulture through the eyes of a sericulture scientist. Dr. Mohandas can be contacted at: tpmdas@gmail.com

The history of sericulture in India dates back to even pre-Buddhist period. Till eleventh century the art of silk fabrics remained well-guarded secret. Japan was pioneer in giving scientific attention to the subject, especially in the utilization of the hybrid vigor. In India sericulture got rich patronage from kings or emperors. The British Raj particularly was interested in sericulture due to the world situation involving China and Japan during the world war periods as also to collect raw material for its own use.

In independent India, initially sericulture was export oriented. The export item was not raw silk, but finished silk fabrics. Today sericulture has gained new importance as agro-economic practice for rural development, generation of self-employment, empowerment of women and export earning. Moreover, sericulture fits in to the scheme of multi- farming system practices in many of the rural villages in India with farmers having marginal land holding.

Presently sericulture production is fast declining Japan. China is the biggest competitor for India being the producer of above 55,000 tons of raw silk. India is a poor second with around 15,000 tons of raw silk production. The capital intensive and labor saving temperate sericulture practiced by Japan achieved the highest level of productivity and quality. In contrast the tropical sericulture in India is labor intensive and low capital input is comparatively very poor in productivity and quality of the silk produced. Japanese sericulture failed to sustain in that country because of the changed socio economic situation there. Although China is the big player in the global silk market especially with the opening up of the marker following the GATT agreements effective from 2005 sericulture is recently showing some decline in that country also recently. India has a good opportunity now to emerge as world leader in the silk scenario. The technical know-how available and being developed is also ready to meet this challenge.

In this context, one aspect needs to be considered before dissecting out the exact issues concerning sericulture development in India. Many socio-economic studies have confirmed that the benefit –cost ratio of sericulture is highest among comparable agricultural cash crops in the country. Sericulture is not amenable to mechanization beyond a point, thus offers great scope for generating rural employment. Further analysis of trends in international silk production suggests that sericulture has a vast growth potential for developing countries. Out of the three countries, i.e., India Japan and China labor efficiency is lowest in India. Cost of production is also lowest (because inputs are given at subsistence level), but it is at the cost of quality, since India produces low quality polyvoltine (multivoltine) yellow cocoons, where as Japan and China produces high quality bivoltine cocoons. Both India and China took up the quality improvement cost reduction programs two decades ago. Now 70% of China’s raw silk production is of bivoltine and white polyvoltine, while India is still a polyvoltine (95%) silk producer.

It is important to look into the real situation in Indian sericulture. All the major commercial silks are produced in the country. However, different races and hybrids of the monophagous silkworm Bombyx mori produce the major portion of silk in India. The gene pool available in the country can be broadly divided in to two groups, low yielding stocks characterized by high adaptability to tropical conditions and the high yielding stocks exhibiting regular diapause, suffer from the low adaptability to the highly variable tropical agro climatic conditions.

To increase productivity and quality of silk there is an urgent need to develop technology suitable for tropical sericulture. Transplanting the technology developed for by the temperate sericulture is neither practical nor economically viable. This is because we have to consider at the same time the agro climatic conditions where the technology is going to be applied as well as the economic status of the technology user.

Sericulture R&D in India demanded the twin requirement of evolving of high yielding breeds and development of the sericulture technology suitable for it. Since the productivity through better conversion to silk is higher in bivoltine silkworm, the shift to bivoltine sericulture will add to reduction. Recent switching to the high yielding mulberry variety from conventional K2 and CSR2x CSR4 from the multivoltine x Pure Mysore x NB₄D₂ are typical examples, through which productivity increased dramatically.

Central Silk Board took up the bivoltine sericulture technology development program (BSTDP: 1991-99) in a bigger way with the cooperation Japan International Cooperation Agency (JICA). R&D was put to full swing to develop various technologies, which were duly test verified on a multi-location base. Shoot system of mulberry cultivation and rearing, which is extensively followed in Japan, is a notable one. In this method shoot cut along with leaf is fed to the silkworms on large rearing racks instead of the individually picked leaves reducing labor cost by 60%. Following the paired row system it is also possible to partially or fully mechanize the plantation. Separate garden for young age rearing (it is generally called Chawki rearing) ensures a healthy crop as the early age rearing is very critical from the nutrition and sanitation point of view.

Water is limiting factor in agricultural system. So to conserve it water shed management concepts are hugely introduced. Drip system is followed to maximize the utility of available ground water. Recycling of seri-waste through composting/ vermi-composting is value addition while helping to reduce contamination of rearing premises. Inter-croping with leguminous plants is also recommended to improve fertility of the soil. In put cost is drastically cut by complementing chemical fertigation with use of biofertilisers (Azatobacter and Vesicular Arboscular Micorhizha). About Rs. 5000/- per ha is saved in this way.

There are new technologies developed or adopted in the field of mounting of worms for cocooning, harvesting etc. Examples are those for fast uniform ripening and better cocoons (rotary mountage). These may involve high investment initially, but in the long run cost effective.

In the field of pest and disease management also the developments are noteworthy. Microsporidiosis or Pebrine, which is trans-ovarially transmitted and thus the most serious disease in silkworm is all most fully controlled by the various mother moth examination methods. Even its immuno-diagnosis and DNA (through polymerase chain reaction) methods are developed for precise identification of the virulent strains. Some pyralids are already identified as alternate host of the pathogen which opens up scope for further studies in these lines. Flacherie is another serious disease condition, which is actually a complex involving certain non-occluded viruses and bacteria, which act either individually or synergistically. Two major ones are Infectious Flacherie Virus (Bm IFV) and Densonucleosis Virus (Bm DNV). Another viral disease of concern is Nuclear Polyhedrosis or grasserie caused by the Bm NPV, and are contained in polyhedra. Among fungal diseases muscardine caused by Beauveria and Metarrhizium; and aspergilosis (agent Aspergillus) are important.

Current stress on disease management is rather on prevention rather than on control. Proper disinfection using slaked lime, formalin and/or bleaching powder, Chlorine dioxide (500 ppm) are found to be most effective. Rearing rooms, appliances and the premises are to be disinfected thoroughly before the start of the crop. Many rearing bed disinfectants ( under the coomercial names like Resham Keed Oushad, Resham Jyothi and Vetcare Vijetha) are developed which are very useful in the control/ secondary contamination of various diseases.

Among the pests uzifly, Exorista sorbillans (=bombysis) of silkworm is the major destructor. Other than the convention use of net various types of traps and chemicals (‘Uzicide’, Uzipowder)were developed to control the pest. Several natural enemies are also used against uzi, viz., Nesolynx thymus (Giroult), N. dipterae (Hymenoptera: Eulophidae), Exoristobia philippinensis Ashmead (Hymenoptera : Encyrtidae ), Dirhinus anthracia Walker (Hymenoptera: Chalcididae). CSR&TI, Mysore has developed a technology to mass multiply and release N. thymus which is found to be very effective in the control of the pest. Some studies involving the use of kairomones is also reported the field application of which is still to be made effective. An IPM package is developed, which along with proper quarantine practices are playing very crucial role in the reduction of spread of the pest.

Although the bivoltine technology is popularized, it is a wide consensus that it is not suitable for all regions and all seasons in India. Moreover, given the higher input cost and the rural situation of sericulture in India the idea of sustainable sericulture is muted. The technologies developed are in a large perspective catering to this aspect also.

Various authors reviewed silkworm breeding in India. As mentioned earlier the polyvoltine races of silkworm and breeds evolved from them dominate Indian sericulture. The production expoits the hybrid vigour of either polyvoltine x polyvoltine or polyvoltine x bivoltine crossings. However, bivoltine silk of high quality is imported to meet the need of power loom sector.

Breeding generally concentrated on the improvement of traits correlated to productivity, which are mostly quantitative in nature and are controlled by polygenes. So attempts to improve these traits needs understanding of their response to selection and the relationship of the selected traits with unselected traits. In silkworm these are observed to be very complex.

Prior to the introduction of the breeds it was either the indigenous (Pure Mysore, Nistari) or the exotic (C’Nichi, Sarupat) pure races, which were exclusively used for rearing. Crossing these races with those from Italy, Russia, Japan, or China several new polyvoltines were evolved. But, these could not make much impact. During the 60s many improved polyvoltine breeds like Kolar Gold, Kollegal Jawan, Mysore Princes, Hosa Mysore were developed. During 1981, CSR&TI, Mysore evolved polyvoltine breeds with shorter larval duration, high silk content, better disease tolerance, better quality and higher yield (e.g.: BL23 & BL24). CSR&TI, Berhampore came up with beneficial mutants evolved though x-ray and chemical mutagenesis; and used these in further crossbreeding programs. Better silk quality and productivity were achieved by using the hybrids BL23 x NB4D2 and BL23 x NB4D2_.

Another approach was to extract inbreds from hybrids. Earlier works on silkworm breeding for high yielding stocks were restricted to temperate areas like Kashmir (J&K), Kalimpong (W.B.)and Dehradun (Uttaranjal). Kalimpong-A (KA) and Kalimpong-B are evolved in this way, which were were very promising in the field. The hybrid KA x NB₄D₂ was also very popular. CSR&TI, Mysore evolved two BV breeds CC1 and CA2 in 1980s which had better cocoon shell ratio compared to that of KA x NB₄D_{2 .}

The target set by the bivoltine development program (BSTDP) was to achieve higher survivability (> 90%) and better silk ratio (>23%). Japanese hybrids with desired qualitative and quantitative traits were chosen as breeding material. Eighteen breeds were evolved out which hybrids of CSR2 x CSR4, CSR2 x CSR5, CSR3 x CSR6 etc., were proved to be highly productive (Pupation rate: 89.7-94.7%; Silk Ratio: 23- 24.4%; Renditta: 5.0-5.6). All these hybrids are authorized by Central Silk Board. Breeding for robustness and breeding for disease tolerance are also under way.

Tremendous strides were made in the field of silkworm genetics, molecular characterization, molecular breeding and to a limited extent in the domain of genetic engineering. Recent developments in these fields open up new ways to overcome the limitations of conventional breeding system. Molecular markers are genome wide, highly specific, phenotype/ environment independent, and are faster to work on. It can considerably reduce the breeding time. There are many robust molecular biological tools available now. Of these isozymes, restriction fragment length polymorphism (RFLP), inter simple sequence repeats (ISSR), random polymorphic DNA (RAPD) sequence tagged sites (STS), and microsatellites are a few to mention. Identification of linked molecular markers is useful in marker assisted selection (MAS), which has made big strides in plant molecular breeding for crop improvement.

Apart from identifying linked markers molecular characterization helps to work out the affinities of gemplasm resources available in the country, which in turn will help to weed out duplicate in the accessions and support the conventional breeder in selecting the right breeding material. Of late DNA markers are extensively used for mapping quantitative trait loci (QTL). However, the quantitative genetics in silkworm as such is poorly worked on.

The use of Bt. cotton of conferring resistance to pest and sunflower plant can be used for production of rubber is now well known. In the same line transgenic mulberry and silkworm is also possible. Genes from any organism can be transferred to mulberry/ silkworm through genetic engineering.

Germline transformation could be effected in B. mori using the piggi Bac transposon. Mos 1 mariner element of Drosophila mouritiana is capable of mediating excision and trasposition events in silkmoth which promise the development of genetic transformation system for the lepidopteran insects.

Accurate diagnosis of silkworm diseases is being made possible by the protein and cDNA based diagnostic kits for Nosema, BmNPV, BmIFV, BmDNV. An immonodiagnostic kit was developed by CSR&TI, Mysore for detection of virus disease. One such kit is being developed at the SeriBiotech Research Laboratory for detecting specific virulent strains of pebrine disease.

In conclusion, it can be said that India can take up the challege of production of high quality silk in required quantity to meet the domestic requirement as well as to earn valuable foreign exchange. The textile sector is also developed to support the agro system so that optimum value addition is possible.