Molecular Characterization of a New Nosema bombycis Strain Detected in Iranian Silkworm Farms.

PURPOSE: Pebrine as the most dangerous disease of silkworm mostly caused by Nosema species has caused huge economic losses. There is no information on the species and the genomic sequences of the pebrine-causing microsporidia in Iran. METHODS: In the present research, we tried to determine the sequences of two regions of rDNA using molecular methods. First, infected larvae and mother moths were collected from several farms in the north of Iran for identification and molecular characterization of microsporidian isolates. After extracting the spores and genomic DNA from the collected samples, two fragments of internal transcribed spacer (ITS) rDNA and small subunit (SSU) rDNA were amplified and sequenced, and registered in NCBI database and then, the phylogenetic tree was drawn. RESULTS: Results showed the obtained sequences (ITS rDNA: Accession No. MZ322002 and SSU rDNA: Accession No. MZ314703) represent a new strain of Nosema bombycis, which differs from the sequences deposited in the NCBI. CONCLUSION: The new N. bombycis strain identified in our study will help in control and management of the pebrine disease by specific detection of the infectious agent.

Gaining insights into the compositional constraints and molecular phylogeny of five silkworms mitochondrial genome.

This study was performed to identify codon usage bias (CUB), genetic similarity and phylogenetic analysis of complete mitochondrial genomes along with separate sequences of 13 protein coding genes per each genome from five types of silkworm including Bombyx mori, Bombyx mandarina, Samia cynthia ricini, Antheraea pernyi and Antheraea assama. Nucleotide composition analysis suggested that AT content was higher than GC content and t-test analysis revealed significance difference (p < 0.01) between AT and GC content. Relative synonymous CUB analysis revealed most over-represented codon ends with A or T. Parity plot analysis revealed both natural selection and mutation pressure influenced CUB of mitochondrial genes while neutrality plot analysis suggested that role of natural selection was higher than mutation pressure. The effective number of codons (ENC) revealed the CUB was low among genes and genomes. In phylogenetic analysis of complete mitochondrial genomes, the Bombyx mori fell in a same cluster with Bombyx mandarina and showed the most similarity (96.7%). In terms of protein coding genes, COX1, COX2 and COX3 showed the most obvious differences. In conclusion, comparative analysis of mitochondrial genomes could be used to identify differences in gene organization, accurate phylogenetic analysis and clustering of different types of silkworms.

Comparison of phenotypic and genetic performance of local silkworm groups and two commercial lines.

Five Iranian native silkworm groups: Baghdad, Khorasan Orange, Guilan Orange, Khorasan Pink, Khorasan Lemon, and 107 and 110 commercial lines (12 families from each breed) were randomly selected and reared during 2003-2005 (five generations in spring and autumn). In each family, 30 male and 30 female cocoons were individually recorded for weight, shell weight and shell ratio. From among the native groups, the highest average in all three traits belonged to Baghdad and Khorasan Pink, and the lowest to Khorasan Orange and Khorasan Lemon. From among the commercial lines, the highest average in all three traits belonged to 107. In comparing heritability for cocoon weight in native groups, the highest heritability belonged to Guilan Orange (0.5147) and Khorasan Orange (0.5036) and the lowest heritability belonged to Khorasan Pink (0.0967). In the two other traits, the highest heritability belonged to Khorasan Orange and Baghdad and the lowest to Khorasan Pink. In the commercial lines, line110 had higher heritability than line107 for cocoon weight and cocoon shell weight. In all the groups, genetic correlations between cocoon weight and cocoon shell weight were high, expect for the Baghdad group. There was medium or low genetic correlation among cocoon weight, cocoon shell weight and cocoon shell ratio.

Comparison of Phenotypic and Genetic Performance of Local Silkworm Groups and Two Commercial Lines

Five Iranian native silkworm groups: Baghdad, Khorasan Orange, Guilan Orange, Khorasan Pink, Khorasan Lemon, and 107 and 110 commercial lines (12 families from each breed) were randomly selected and reared during 2003-2005 (five generations in spring and autumn). In each family, 30 male and 30 female cocoons were individually recorded for weight, shell weight and shell ratio. From among the native groups, the highest average in all three traits belonged to Baghdad and Khorasan Pink, and the lowest to Khorasan Orange and Khorasan Lemon. From among the commercial lines, the highest average in all three traits belonged to 107. In comparing heritabihty for cocoon weight in native groups, the highest heritabihty belonged to Guilan Orange (0.5147) and Khorasan Orange (0.5036) and the lowest heritabihty belonged to Khorasan Pink (0.0967). In the two other traits, the highest heritabihty belonged to Khorasan Orange and Baghdad and the lowest to Khorasan Pink. In the commercial lines, linellO had higher heritabihty than linel07 for cocoon weight and cocoon shell weight. In all the groups, genetic correlations between cocoon weight and cocoon shell weight were high, expect for the Baghdad group. There was médium or low genetic correlation among cocoon weight, cocoon shell weight and cocoon shell ratio.