Phenotypic variation in larval and cocoon characters of the domesticated silkworm, Bombyx mori L., during selection

Professorial Chair Lecture

Development Fund Professorial Chair Lecture

Place

Biological Sciences Bldg. Room C-105, UPLB, College, Laguna

Date

4-11-2003

Abstract

The UPLB Sericulture research team, through the financial assistance of JICA and FIDA, developed lines of the domesticated silkworm, Bombyx mori, adapted to local ambient conditions. Eight inbred lines were established after more than 15 generations of selective breeding, 7 of which have survived to this day. In the process of selection, phenotypic variability was noted in all stages of the life cycle of this holometabolous insect. This lecture, however, focuses on the morphological variation expressed in the larval and cocoon stages. In consideration of the relevance of this research to the sericulture industry, selective breeding prioritized characteristics of commercial importance such as synchronicity in hatching and larval development, high survival rates, uniformity of cocoon shape, as well as larger and heavier cocoons with a high cocoon shell ratio (CSR). It was also essential to consider good filatural qualities such as fine and long filaments, which however, are beyond the scope of this paper. Among the 7 lines, CN144 consistently proved to be superior to the others, followed by LBS6 and LBS7. Guanong is also a promising line, but the established lines CJ102K, Kinshu x Showa and Shoukou x Ryuuhaku need further selection, most especially with reference to low quantitative variation, as well as tolerance to the warm, humid lowland conditions. With reference to larval markings, 100% of LBS7 silkworms had the plain larval marking (p), whereas all larvae of the 6 other lines expressed the normal larval marking (+°). As of December 2002, 99.1% of LBS6 and 95.2% of LBS7 cocoons were oblong, but further selection is still needed for CJ102K and CN144, which produced 78.2% and 88.9% peanut-shaped cocoons, respectively. Two field tests of hybrids between LBS7 and the lines CJ102K and CN144 were conducted January-March and June-August 2002, simultaneously at UPLB SBEPC and the FIDA Egg Multiplication and Production Center at Wangal, Benguet. In both rearing sites, the growth performance and cocoon production of the hybrids between LBS7 and CN144 proved to be superior to that of the hybrids between LBS7 and CJ102K. Furthermore, the rearing trials showed that all strains performed far better at Benguet than at Los Baños with respect to all parameters investigated. Analyses have shown that the expressed variation in quantitative characters is strongly influenced by the rearing environment, i.e. these characters are essentially ecophenotypic in nature.

Location

UPLB Main Library Special Collections Section (USCS)

College

College of Arts and Sciences (CAS)

Language

English

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