Isolating silkworm genomic DNA without liquid nitrogen suitable for marker studies

Genomic DNA was isolated from posterior silk gland of silkworms, Antheraea assama. Absolute alcohol was used as tissue fixing solution instead of grinding in liquid nitrogen, which yielded high molecular weight DNA (>40 kb). Samples yielded similar amount of DNA when fixed in absolute alcohol (400 μmg/g of silk gland tissue) and ground in liquid nitrogen (456 μmg/g of silk gland tissue). RAPD profile of the isolated DNA revealed high degree of polymorphism. The silkworms were analysed using 50 random primers among which 36 polymorphic primers gave 309 amplicons. The average amplicons per primer found to be 8.58 and 94.82% amplicons were polymorphic. Cluster analysis based on Jaccard’s similarity coefficients resulted in the formation of two main clusters with S9 on one cluster and the remaining strains on the other cluster. Jaccard’s similarity coefficients ranged from 0.122 to 0.863 indicating a high level of genetic diversity within muga silkworm collection. Isolated DNA was also suitable for cloning and restriction enzyme digestion. This method does not require liquid nitrogen for fixation, grinding or storage at -80°C, making it advantageous over other common protocols.Key words: Genomic, silkworms, muga, molecular breeding

Analysis of genetic diversity of muga silkworm (Antheraea assamensis, Helfer; Lepidoptera : Saturniidae) using RAPD-based molecular markers

Eleven populations of muga silkworm, Antheraea assamensis Helfer, the golden silk yarn producer of northeast India, was subjected to RAPD marker analysis in order to assess its genetic diversity. The genomic DNA extracted from muga silkworms were analysed using 50 random primers among which 36 polymorphic primers generated 309 bands. RAPD profile of the isolated DNA revealed a high level of genetic polymorphism. The average amplicons per primer was found to be 8.58, and 94.82% amplicons were polymorphic. Cluster analysis based on Jaccard’s similarity coefficients resulted in the formation of two main clusters with one population on one cluster and the remaining on the other cluster.Jaccard’s similarity coefficients ranged from 0.122 to 0.863 indicating a high level of genetic diversity within muga silkworm collection. The study concluded that, although there lays little morphological differences among the collected muga silkworm populations, the populations are highly polymorphic which might have enabled the silkworm to survive under a restricted geographical location, that is north east region of India only but under diverse climatic conditions for a long period. This study maybe useful in identifying diverse genetic stocks of A. assamensis, which may be conserved on a priority basis

Studies on secondary metabolites of Som ( Persea bombycina Kost), a primary host plant of muga silkworm (Antheraea assamensis Helfer)

The host plant selection behaviour or feeding preferences of the insects are largely mediated by the presence and distribution of secondary metabolites in plants. Quantitative estimation of few secondary metabolites and HPLC analysis of phenolic compounds were carried out from the leaves of Som plant (Persea bombycina Kost) which is a primary metabolite of the shimmering yellow golden silk yarn producer, the muga silkworm (Antheraea assamensis Helfer). β –sitosterol content in the tender leaves was significantly the highest (1.06%) over semi-mature or mature leaves, whereas Chlorogenic acid content was more in medium leaves (2.06%). Phytic acid content was significantly higher in mature leaves (2310.05 mg/100g), total phenol in tender leaves (1.946%), ADF in mature leaves (26.50%), ADL in mature leaves and tannin in tender leaves (6.71%). Purified phenolic extract when subjected to HPLC analysis, 6 prominent peaks were observed and screening with standard indicates Peaks 1, 2, 3 and 6 correspond to Chlorogenic acid, catechol, Morin and gallic acid, respectively. Keywords: Som, Persea bombycina, Muga silkworm, Antheraea assamensis, secondary metabolites, HPLC analysis

Analysis of Genetic Diversity of Persea bombycina ‘‘Som’’ Using RAPD-Based Molecular Markers

The utility of RAPD markers in assessing genetic diversity and phenetic relationships in Persea bombycina, a major tree species for golden silk (muga) production, was investigated using 48 genotypes from northeast India. Thirteen RAPD primer combinations generated 93 bands. On average, seven RAPD fragments were amplified per reaction. In a UPGMA phenetic dendrogram based on Jaccard’s coefficient, the P. bombycina accessions showed a high level of genetic variation, as indicated by genetic similarity. The grouping in the phenogram was highly consistent, as indicated by high values of cophenetic correlation and high bootstrap values at the key nodes. The accessions were scattered on a plot derived from principal correspondence analysis. The study concluded that the high level of genetic diversity in the P. bombycina accessions may be attributed to the species’ outcrossing nature. This study may be useful in identifying diverse genetic stocks of P. bombycina, which may then be conserved on a priority basis

Ionization yield measurement in a germanium CDMSlite detector using photo-neutron sources

Two photo-neutron sources, $^{88}$Y$^{9}$Be and $^{124}$Sb$^{9}$Be, have been used to investigate the ionization yield of nuclear recoils in the CDMSlite germanium detectors by the SuperCDMS collaboration. This work evaluates the yield for nuclear recoil energies between 1 keV and 7 keV at a temperature of $\sim$ 50 mK. We use a Geant4 simulation to model the neutron spectrum assuming a charge yield model that is a generalization of the standard Lindhard model and consists of two energy dependent parameters. We perform a likelihood analysis using the simulated neutron spectrum, modeled background, and experimental data to obtain the best fit values of the yield model. The ionization yield between recoil energies of 1 keV and 7 keV is shown to be significantly lower than predicted by the standard Lindhard model for germanium. There is a general lack of agreement among different experiments using a variety of techniques studying the low-energy range of the nuclear recoil yield, which is most critical for interpretation of direct dark matter searches. This suggests complexity in the physical process that many direct detection experiments use to model their primary signal detection mechanism and highlights the need for further studies to clarify underlying systematic effects that have not been well understood up to this point