First Report on the Characterization of Genetic Diversity of Philippine-reared Bombyx mori Strains Based on COI and ITS2

Abstract

The mulberry silkworm, Bombyx mori, is known to produce silk and was introduced to the Philippines from China, Japan, Korea, and India. The silkworm germplasm in the Philippines is sourced from three centers located in regions that vary in climatic conditions: Philippine Textile Research Institute–Technology Center Misamis Oriental (PTRI-TCMO); Department of Science and Technology– Cordillera Administrative Region (CAR) in La Trinidad, Benguet; and the Don Mariano Marcos Memorial State University–Sericulture Research and Development Institute (DMMMSU-SRDI), La Union. To date, associated information with the centers’ germplasm constitutes differences in biological and productive traits such as yield and quality of raw silk. It lacks genetic information on strain diversity, which provide basis for the efficient selection of parental strains with traits of economic interest. This study aimed to characterize, for the first time, the genetic diversity of 17 pure lines as parental strains. Genetic variation was evaluated using the cytochrome c oxidase 1 (COI) gene and internal transcribed spacer 2 (ITS2). BLAST analysis of the COI and ITS2 sequences confirmed the identity of B. mori strains. Phylogenetic trees constructed from COI sequences formed a monophyletic clade, while the trees based on ITS2 sequences formed two distinct clusters. The pairwise distances based on the Kimura 2-parameter (K2P) model between the B. mori strains ranged from 0–0.003 for COI and from 0–0.002 for ITS2, indicating low genetic variation for the corresponding molecular markers. Variation in the COI gene determined four nucleotide changes while variations in the ITS2 sequences determined four to six nucleotide changes, except for one strain with higher nucleotide change. This study reports that the use of COI and ITS2 as markers was not able to genotypically differentiate the 17 strains, which appear different in terms of phenotypic characters, suggesting the use of other molecular markers to characterize not only the 17 strains but all other strains in the germplasm.