2. Conservation of Silkworm Genetic Resources in Korea

2.1 Present status of germplasm maintenance

For the safe conservation and insurance of silkworm gene resources and in adherence to national protectionism according to Convention on Biological Diversity and utilization for basic and practical study, the Dept. of Sericulture and Entomology now conserves 340 silkworm strains. These 340 strains (321 registered strains and 19 unregistered strains) were classified largely by their origin, voltinism, moltinism (Table 1).

Table 1. The present status of conservation of 321 silkworm strains

The criteria for classifying silkworm are based on their origin, chemical characteristics. In RDA, the classification method based on silkworm's origin is used as the standard method when examine the characteristics of cocoon. Silkworm strains can be largely classified into five major strains: Japanese, Chinese, Tropical, European, and Korean.

Fig. 1 Various patterned silkworms

2.2 Management and utilization of germplasm resources

2.2.1 Silkworm gene resources conservation plan

2.2.1.1 Silkworm egg conservation plan for an emergency

The 321 silkworm strains and 150 strains for breeding are dispersed at Jeonbuk and Gyeongnam Agricultural Technique Institute in case of a natural disaster and an emergency like war. Other institutes conserve silkworm eggs of on their own.

2.2.1.2 Dispersal conservation of major silkworm gene resources and breeding races

Jeonbuk(Jenoju) and Gyeongnam(Jinju) National Institute of Agricultural 4Technology: 321 races each place.

Table 2. Number of conserved silkworm gene in the related office of each province

2.2.1.3 Long-term conservation study of silkworm gene resources

The silkworm gene resources are conserved in cold stage as eggs during winter and succeeded in the next year and development of labor-saving and long-term conservation are ongoing as a part of safe succession and management technique development. The earlier mentioned is the standard refrigeration method and can preserve eggs for a year. Thus, the 321 strains which are conserved succeeded every year and there are always possibility of race character change by accident such as mixing races. Moreover, development of long-term conservation is required because the efforts to succeed the races is increasing with the import of strain as a new gene resources and appearance of new mutant strain. The longest conservation system now used is double-refrigeration method, which can preserve eggs for 450 days maximum if eggs are collected in June and preserved to hatching period in August. Now long-term gene conservation study is ongoing in RDA, it's first long-term conservation of silkworm eggs using egg dormancy makes progress aiming at 2 year conservation. And freezing conservation of gonad (testis and ovary) and reproductive cell(ovum and sperm), and conservation of fertilized egg at very low temperature are being planned as a medium-long term plan. In Japan, utilization of egg dormancy and egg conservation by ling-term refrigeration are already at the stage of practical use. Moreover, study of semi-permanent conservation of gene resources by freezing of gonad and permanent conservation by freezing fertilized egg at very low temperatures is under progress.

2.3 Development of germplasm resources

2.3.1 Promoting system

This framework depicts the process in the promoting system.

2.3.2 Breeding material

It is easy to cause mutation in natural condition by giving artificial stimulation to eggs, larvae, pupa, and moths, so mutant strains that show various characteristics can be bred easily. Samples of such strains are Yangwonjam (: patterned, : no patterned) and Hwangwonjam (: yellow cocoon,: white cocoon), which are sex-limited races. The other races used as breeding material are large body-sized strain for silkworm dry powder and non-cocoon making strain for mass production of Dongchoonghacho.

2.3.3 Living body utilization (utilization of silkworm as living factory)

Through the long breeding period of 500 years, silkworm moths are domesticated by humans and have lost their flying ability. Silkworm mutant is utilized for new race crossbreeding and examining mutation caused by environment and chemicals. The color of normal silkworm eggs is yellow but there are recessive colors such as white, yellow, red. If two silkworm moth, one with normal egg color and the other with white egg color, are crossbred, F₁ shows normal egg color. If a food additive is fed or injected to a normal color cocoon or a moth emerged from the cocoon is crossbred with white egg color moth, the crossbred eggs show white color, because mutation happened to the loci response to white egg color. The silkworm female moth lays about 500 eggs in one night, so mutation by chemicals can be easily detected.