Molecular Markers for Biomass Traits: Association, Interaction and Genetic Divergence in Silkworm Bombyx mori

Improvement of high yielding, disease resistant silkworm strains became imminent to increase production of silk, which is a major revenue earner for sericulturists. Since environment interacts with phenotype, conventional breeding did not result in commendable yield improvement in synthetic strains of silkworm, Bombyx mori. Identification of DNA markers associated with different economically important biomass traits and its introgression could assist molecular breeding and expression of stabilized high yielding characters, but genetic basis of most quantitative traits in silkworm is poorly understood due to its polygenic control. Correlation analysis (R = 0.9) revealed significant interrelation among biomass traits viz., larval duration (TLD), larval weight (LWT), cocoon weight (CWT), shell weight (SWT), shell ratio (SR) and floss content. PCR using inter simple sequence repeat (ISSR) primers revealed 92% polymorphism among 14 tropical and temperate strains of B. mori, with average diversity index of 0.747. Stepwise multiple regression analysis (MRA) selected 35 ISSR markers positively or negatively correlated with different biomass traits, illustrated polygenic control. ISSR marker 830.81050bp was significantly associated with LWT, CWT, SWT, SR and floss content, indicated its pleiotropic role. Two ISSR markers, 835.51950bp and 825.9710bp showed significant association with floss content and TLD. These markers were segregated in F2 generation and Chi-square test confirmed (χ2 = ~45; P < 0.05) its genetic contribution to the associated biomass traits. Strains, with both positively and negatively correlated markers, had intermediate mean value for biomass traits (eg. SWT = 0.17 ± 0.014 g in GNM and Moria) indicated interaction of loci in natural populations. Low yielding Indian strains grouped together by Hierarchical clustering. Chinese and Japanese strains were distributed in the periphery of ALSCAL matrix indicated convergence of genetic characters in Indian strains. Average genetic distance between Chinese strains and Indian strains (0.193) significantly (P < 0.01) varied from that between Chinese and Japanese strains. Interaction of loci and allelic substitutions induced phenotypic plasticity in temperate B. mori populations on tropic adaptation in India. These outcomes show possibility to combine favorable alleles at different QTL to increase larval, cocoon and shell weight

Genetic diversity and population structure of Indian golden silkmoth (Antheraea assama)

Background The Indian golden saturniid silkmoth (Antheraea assama), popularly known as muga silkmoth, is a semi-domesticated silk producing insect confined to a narrow habitat range of the northeastern region of India. Owing to the prevailing socio-political problems, the muga silkworm habitats in the northeastern region have not been accessible hampering the phylogeography studies of this rare silkmoth. Recently, we have been successful in our attempt to collect muga cocoon samples, although to a limited extent, from their natural habitats. Out of 87 microsatellite markers developed previously for A. assama, 13 informative markers were employed to genotype 97 individuals from six populations and analyzed their population structure and genetic variation. Methodology/Principal Findings We observed highly significant genetic diversity in one of the populations (WWS-1, a population derived from West Garo Hills region of Meghalaya state). Further analysis with and without WWS-1 population revealed that dramatic genetic differentiation (global FST = 0.301) was due to high genetic diversity contributed by WWS-1 population. Analysis of the remaining five populations (excluding WWS-1) showed a marked reduction in the number of alleles at all the employed loci. Structure analysis showed the presence of only two clusters: one formed by WWS-1 population and the other included the remaining five populations, inferring that there is no significant genetic diversity within and between these five populations, and suggesting that these five populations are probably derived from a single population. Patterns of recent population bottlenecks were not evident in any of the six populations studied. Conclusions/Significance A. assama inhabiting the WWS-1 region revealed very high genetic diversity, and was genetically divergent from the five populations studied. The efforts should be continued to identify and study such populations from this region as well as other muga silkworm habitats. The information generated will be very useful in conservation of dwindling muga culture in Northeast India

Genetic diversity and differentiation among populations of the Indian eri silkworm, Samia cynthia ricini, revealed by ISSR markers

Samia cynthia ricini (Lepidoptera:Saturniidae), the Indian eri silkworm, contributes significantly to the production of commercial silk and is widely distributed in the Brahmaputra river valley in North-Eastern India. Due to over exploitation coupled with rapid deforestation, most of the natural populations of S. cynthia ricini are dwindling rapidly and its preservation has become an important goal. Assessment of the genetic structure of each population is a prerequisite for a sustainable conservation program. DNA fingerprinting to detect genetic variation has been used in different insect species not only between populations, but also between individuals within a population. Since, information on the genetic basis of phenotypic variability and genetic diversity within the S. cynthia ricini populations is scanty, inter simple sequence repeat (ISSR) system was used to assess genetic diversity and differentiation among six commercially exploited S. cynthia ricini populations. Twenty ISSR primers produced 87% of inter population variability among the six populations. Genetic distance was lowest between the populations Khanapara (E5) and Mendipathar (E6) (0.0654) and highest between Dhanubhanga (E4) and Titabar (E3) (0.3811). Within population, heterozygosity was higher in Borduar (E2) (0.1093) and lowest in Titabar (E3) (0.0510). Highest gene flow (0.9035) was between E5 and E6 and the lowest (0.2172) was between E3 and E5. Regression analysis showed positive correlation between genetic distance and geographic distance among the populations. The high GST value (0.657) among the populations combined with low gene flow contributes significantly to the genetic differentiation among the S. cynthia ricini populations. Based on genetic diversity, these populations can be considered as different ecotypes and in situ conservation of them is recommended

A study of prognosis and outcome of COVID-19-infected hypertensive patients on angiotensin-converting enzyme inhibitors/angiotensin receptor blockers

Background and Objective: COVID-19 is a pandemic caused by the virus severe acute respiratory syndrome coronavirus-2. The mortality in susceptible populations with chronic pulmonary disease, cardiac ailments, kidney disease, diabetes, and hypertension is high. While the role of angiotensin-converting enzyme inhibitors (ACEi)/angiotensin receptor blockers (ARBs) in contracting novel coronavirus has clearly been elucidated, there remains uncertainty in the prognosis and outcome of COVID-19-infected patients on ACE inhibitors and ARBs. The current study was conducted to find whether these medications bore any significance in the prognosis and outcome of hypertensive patients with COVID-19 infection. Materials and Methods: This is a retrospective cohort study. We studied 96-admitted hypertensive patients with pneumonia due to COVID-19 in Krishna Rajendra Hospital at Mysore during April 2021. Patients were categorized into two groups based on antihypertensive treatment: (1) Those on ACEi/ARBs (n = 33) and (2) Those on non-ACEi/ARBs (n = 66). We analyzed the parameters such as duration of hypertension, comorbidities, mode of oxygen/pressure support delivery, duration of hospital stay, and mortality among the two groups. Results: 65.6% of patients were on non-ACEi/ARBs, 10.4% on ACE inhibitors, and 24% on ARBs. Of the patients on non-ACEi/non-ARBs, 51% were on supplemental oxygen, 20.8% were on NIV, 6.3% were intubated, and 21.9% did not require oxygen. Of those on ACEi, 63.6% were on supplemental oxygen, 15.2% were on NIV, none were intubated, and 21.2% did not require oxygen. Of those on ARBs, 53.3% were on supplemental oxygen, 18.5% were on NIV, 5.4% were intubated, and 22.8% did not require oxygen. 62.5% of patients on non-ACEi/ARBs recovered, whereas 37.5% succumbed. 83.3% of patients on ACEi recovered, whereas 16.7% succumbed. 65.2% of patients on ARBs recovered, whereas 34.8% succumbed. There was no significant correlation between non-ACEi/ARBs, ACEi, and ARBs with duration of hypertension (P = 0.092), sex (P = 0.189), mode of oxygen/pressure support delivery (P = 0.313), ward/intensive care unit stay (P = 0.624), and the final outcome of the patient (P = 0.734). Conclusion: In the population studied, the use of ACEi/ARBs in COVID-positive hypertensives was not associated with adverse outcomes as compared to those on non-ACEi/non-ARBs

PCR detection of densonucleosis virus isolates in silkworm (Bombyx mori) from India and their nucleotide variability

56-60Densonucleosis virus (DNV) is one of the pathogenic viruses of the commercially valuable silkworm, Bombyx mori. It causes flacherie disease, mostly as combined infection with other pathogens like bacteria, which accounts for the significant loss of cocoons in sericulture. Two isolates of DNV from B. mori, DNV1 and DNV2 have been previously identified on the basis of their sequences. After infection with purified isolates of DNV in some commonly used silkworm strains, viz. Nistari, C’nichi, NB1 and Guangnnong Marked, the polymerase chain reaction (PCR) was conducted using DNV1 and DNV2 primers. DNV1 primers generated a distinct profile in the B. mori strains, whereas DNV2 produced single monomorphic band in all the screened strains. Sequence of one of the prominent fragments generated by the DNV1 primer exhibited very high degree of nucleotide variability from that of Japanese DNV1 isolate, but the sequence of DNV2 showed near to complete similarity. Besides, the study demonstrates that PCR technique could be used to diagnose the DNV presence/absence in silkworm strains without sacrificing the larvae and the results could be used in breeding programmes

Molecular evaluation of bivoltine, polyvoltine and mutant silkworm (Bombyx mori L.) with RAPD, ISSR and RFLP-STS markers

188-194Mulberry silkworm (Bombyx mori L.), the most important silk producing insect, exhibits wide diversity in morphological and biometric characters. Characterization of vast genetic resources based on the morphological and quantitative traits is not solely dependable as the phenotypic traits are influenced by environment. In order to study genetic relatedness of the selected and varied genotypes, six each of the bivoltine, polyvoltine silkworm accessions and mutant stocks, were studied with RAPD, ISSR and RFLP-STS markers. Twelve RAPD primers generated 172 markers of which 161 were polymorphic, generating 93.60% polymorphism. Pair-wise genetic divergence varied from 0.209 between Mysore Princess and Rong Diazo to 0.588 between Boropolu and TMS-35. The ISSR primers generated 156 markers of which 132 were polymorphic thus generating 84.62% polymorphism. The pair-wise genetic diversity among the genotypes varied from 0.189 between Rong Diazo and BL-23 to 0.438 between MU-10 and TMS-35. Similarly, 10 RFLP-STS primers produced a total of 69 bands, out of which 53 were polymorphic thus realizing 75.6% polymorphism. Genetic distance varied from 0.242 between Nistari-M and BL-23 to 0.730 between Fengshong and TMS-17. On clustering with UPGMA and principal component analysis (PCA), RAPD and ISSR markers clearly discriminated the bivoltines and multivoltines and a multivoltine Tamil Nadu white occupied the positions among bivoltines, since it has bivoltine parentage. Boropolu, an original land race from North East India, and Feng shong, a Chinese silkworm strain, also showed a closer genetic relationship