Molecular Evidence Supporting the Natural Defense of the Lamerin Breed of Silkworm (Bombyx mori L.) to Nosema bombycis Infection

Nosema bombycis Naegeli, a microsporidian and the causative agent of Pebrine disease, poses a significant threat to silkworm (Bombyx mori) populations and the sericulture industry. While most strains are highly susceptible, the Lamerin breed has shown co-existence with microsporidia without affecting its survivability but the said study lacks molecular confirmation. This study is aimed to evaluate the infection response of Lamerin and the susceptible CSR2 breed under simulated natural conditions. Oral administration of N. bombycis spores resulted in ~30% mortality in Lamerin, compared to over 90% in CSR2. Quantitative RT-PCR revealed early upregulation of Nosema-specific genes in both breeds, but Lamerin showed sustained induction of immune-related genes, including antimicrobial peptides, serpins, and cuticular proteins, from 24 to 96 hours post-infection. These findings provide molecular evidence for enhanced tolerance or resistance in the Lamerin breed, with potential implications for breeding disease-resistant silkworm lines.