# Genetic and morphological variation in the Colombian Bombyx mori germplasm: A first SSR-based assessment

## TL;DR

This study assesses the genetic and physical diversity of Colombian silkworms using molecular and morphological markers to support breeding and conservation efforts.

## Contribution

The first SSR-based assessment of genetic and morphological variation in Colombian Bombyx mori germplasm.

## Key findings

- Morphological traits like voltinism and cocoon color were most effective in differentiating silkworm breeds.
- Commercial lines showed higher molecular homogeneity due to selective breeding, while ICA and NC lines showed genetic stability.
- Combined use of molecular and morphological markers improved classification of silkworm germplasm for breeding.

## Abstract

Centuries of domestication have produced over 4000 Bombyx mori L. ecotypes, many of which share similar morphological and reproductive traits that hinder genetic improvement and differentiation. In Colombia, 67 silkworm lines are maintained; however, their industrial potential remains underutilized due to the lack of genetic and phenotypic data. To address this, we evaluated the genetic and morphological variability of the Colombian B. mori germplasm using 13 phenotypic traits and 23 simple sequence repeat (SSR) markers, 17 of which were polymorphic. Morphological traits such as voltinism (H’ = 4.22), larval markings (H’ = 4.057), and cocoon color (H’ = 3.849) were the most informative in differentiating breeds. The SSR markers revealed 2–11 alleles per locus, with PIC values ranging from 0.05 to 0.72 (median = 0.46). The AMOVA results revealed that 96% of the genetic variation occurred within populations, with only 4% among them. Commercial lines presented greater molecular homogeneity, likely due to intensive selective breeding, whereas ICA and unknown-origin (NC) lines presented no significant deviation from Hardy‒Weinberg equilibrium, suggesting greater genetic stability and potential for improving inbred breeds. Additionally, the molecular markers allowed for the classification of lines according to breeder-defined categories. Although several lines retained ancestral morphological characteristics, Japanese and Chinese lines presented low heterozygosity, likely due to bottlenecks associated with hybrid development programs. Morphological markers also revealed patterns on the basis of line provenance, offering clues to the origins of unclassified strains. A few lines clustered similarly across both the morphological and molecular dendrograms, indicating conserved trait patterns. The combined use of morphological and molecular markers allowed for a more comprehensive classification of the silkworm germplasm, identifying candidate lines for future breeding efforts. These findings provide new insights into the genetic diversity of B. mori in Colombia and offer a valuable baseline for conservation and hybrid development programs aimed at enhancing vigor and productivity.