Genetic stability analysis of diapause-induced multivoltine silkworm Bombyx mori germplasm using inter simple sequence repeat markers

摘要

Conservation of silkworm [Bombyx mori L. (Lepidoptera: Bombycidae)] germplasm aids in prevention of genetic erosion and race extinction. Multivoltine silkworm germplasm maintenance involves rearing five generations per year and this requires expenditure, manpower, and infrastructure, in addition to frequent exposure of the silkworms to diseases, pests, and predators. To minimize these problems, an alternative protocol was developed by way of induction of egg diapause in the multivoltine silkworms through rearing of the fourth and fifth instars at low temperature (18-20 pC) under regulated photoperiod (L6:D18). This method allowed induction of egg diapause in the selected races at levels ranging from 26 to 94% and the diapause-induced eggs were maintained under cold preservation conditions. The stability of genotypic characters was confirmed in the diapause-induced silkworm batches after the seventh generation, by comparison with control batches of silkworm using inter simple sequence repeat-polymerase chain reaction (ISSR-PCR). Analysis of Nei's genetic distance for the different races indicated no significant variation between control and diapause-induced races. This reveals that all the selected races maintained genetic stability even after the seventh generation at the phenotypic and molecular level. Hence, it can be concluded that induction of egg diapause is an appropriate alternative method to preserve multivoltine races for longer periods of time.