Genetic variability and genetic structure of wild and semi-domestic populations of tasar silkworm (Antheraea mylitta ) ecorace Daba as revealed through ISSR markers.

The genetic diversity in the wild and semi-domestic populations of Daba ecorace of Antheraea mylitta was studied to ascertain the distribution of variability within and among populations of semi-domestic bivoltine (DB), trivoltine (DT) and nature grown wild populations (DN) with inter-simple sequence repeat (ISSR) markers. A total of 138 markers were produced among 56 individuals of the three populations, of which 98% were polymorphic. For the individual populations, the percentage polymorphism was 58.69, 52.9 and 77.54 for DB, DT and DN, respectively. Average number of observed (1.791+/- 0.408) and effective alleles (1.389+/-0.348) was also high in the wild populations in comparison to the bivoltine and trivoltine semi-domestic populations. Genetic diversity (H(t)) in DB, DT and DN was 0.180+/- 0.033, 0.153+/- 0.032 and 0.235+/- 0.033, respectively and within-population genetic diversity (H(s)) ranged from 0.166 to 0.259 with a mean of 0.189. Mean gene differentiation (G(ST)) was found to be 0.25. Shanon's diversity index was 0.278, 0.237 and 0.361 for DB, DT and DN and overall it was 0.391. Gene flow (N(m)) among the populations was 1.509. The dendrogram produced by UPGMA with Dice's genetic distance matrices resulted in the formation of three major clusters separating the three populations. Considerable intra- and inter-population variability is found in all three populations. The population structure analysis further suggests that the semi-domestic populations of Daba ecorace are at the threshold of differentiating themselves. The high genetic variability present within wild Daba population of A. mylitta is of much importance for conservation as well as utilization in systematic breeding program.

Molecular analysis of divergence in tachinid Uzi (Exorista sorbillans) populations in India.

Exorista sorbillans is a tachinid endoparasitoid of silkworm, Bombyx mori, and is globally known as uzi. It causes economic injury to the cocoon crop in silkworm cultivating areas of India, except those above 400 m above mean sea level (AMSL) in the foothills of the Himalayas (Darjeeling). It is reported that the sericulture tract of south India became infected with this pest only since 1980 through an accidental transportation of cocoons from West Bengal. To ascertain whether the genome of this parasitoid is differentiating into discrete gene pools in contrasting geo-climatic conditions, molecular profiling of four populations (Es (Annatapur), Es(Ramanagaram), Es (Channapatna) and Es(Kodathi) from south India and Es(Murshidabad) from Murshidabad, West Bengal was undertaken with 13 ISSR, 3 RAPD and six non-random primers designed from various repeat sequences of B. mori . MANOVA indicated significance for the Roy's largest root estimate (55.4; F =18.47; p = 0.002) for the variability contributed by the replication. Further, hierarchical clustering done on the basis of Euclidean distance matrix and Nei's unbiased Phylip clustering put Es(Murshidabad) at the maximum distance from those of south India and 29 markers could also be identified which significantly differentiateEs(Murshidabad) from others. However, Nei's statistics for gene diversity in sub-populations reveal considerably high gene-flow (3.44 and 2.51) among the populations around Bangalore. The gene-flow between Es(Murshidabad) and other population is lowest but cannot be ignored. The comparison of endosymbiont specific 16SrRNA and fts Z gene (partial) sequences through clustalW (gcgMSF) revealed a closer relationship of Es(Murshidabad) with Es(Annatapur) and Es (Ramanagaram) and is not congruent with the relationships discussed above. The significance of this maiden study with a tachinid fly-pest is discussed in the context of understanding the diversification of Uzi fly-pest and also establishing this pest as a relevant biological material for studying microevolution in future.

Molecular genetic approach for identifying markers associated with yield traits in the silkworm, Bombyx mori using RFLP-STS primers.

Bombyx mori, the mulberry silkworm, exhibits wide variability in yield and developmental attributes. The genetics of yield expression, shown to be of polygenic nature, is poorly studied in silkworm. To identify markers associated with 10 selected yield traits, multiple regression analysis (MRA) and discriminant function analysis (DFA) were applied on 64 markers generated with eight RFLP-derived sequence-tagged-site (STS) primers on the genomic DNA of 20 silkworm stocks of different origin and diverse yield potential. The analyses led to the identification of ten markers showing significant association with the different yield traits. The markers could classify the stocks according to yield potential, irrespective of their origin and status of diapause. Trait means were significantly different for stocks with and with out the associated marker. The inheritance of a marker G2(1300bp), selected at the first step of MRA for five yield traits was shown to segregate in 1:1 ratio in the F2 progeny from a cross between two divergent stocks. The relevance of the STS primers is discussed in the context of applying multiple regression model for identifying markers associated with yield expression and suitability for molecular breeding work in B. mori for yield improvement.

Identification of ISSR markers associated with productivity traits in silkworm, Bombyx moni L.

Bombyx mori L., commonly recognised around the world as the mulberry silkworm, is characterized by a wide variability in yield and developmental traits, which have been proven through conventional genetic analysis to be of polygenic nature. A large number of morpho-biochemical traits and RFLP and RAPD markers are mapped on different linkage groups, but to this point very little attention has been given to unravelling the genetics of yield traits. To address this issue, polymorphic profiles of 147 markers generated with 12 ISSR primers on the genomic DNA of 20 silkworm stocks of diverse yield status were subjected to multiple regression and discriminant function analyses (DFA). This led to the identification of eight markers generated by six primers, which demonstrated high beta-coefficient indices of -0.451 to -0.940. Furthermore, a significant difference between the yield traits for stocks with and without the specific marker could also be established. The inheritance pattern of one marker, L13800bp, identified at the first step of selection of markers through stepwise regression analyses for five yield parameters is discussed in the context of applying multiple regression analysis for establishing association, if not linkage, between a group of DNA markers and a particular yield trait of polygenic nature and using such markers in molecular marker-assisted breeding programs.