Characterization and diversity assessment in coconut collections of Pacific Ocean Islands and Nicobar Islands

Characterization and genetic diversity assessment among 30 conserved coconut accessions collected from Pacific Ocean Islands and Nicobar Islands for morphological traits, physico-chemical traits of tender nut water, leaf biochemical parameters and molecular characterization by using random amplified polymorphic DNA (RAPD) markers were undertaken at World Coconut Germplasm Centre, Andaman. Significant variations were observed for most morphological and nut component traits. Out of the 30 accessions characterized, four accessions, namely, Niu Leka, Hari Papua, Niu Oma and Nikkore were dwarfs among which Niu Leka was identified as a unique dwarf with higher copra content. A dendrogram of genetic relationship obtained through RAPD markers showed distinct variation with 66% in all accessions. The average polymorphic information content (PIC) value of 13 selected primers was 0.29 and maximum and minimum PIC values was 0.46 and 0.17 for primers OPF-19 and OPH-25, respectively. Cluster analysis by UPGMA method grouped the accessions into two major clusters. The results will be useful in the selection among these conserved accessions for specific traits for future utilization in crop improvement initiatives based on their performance for different desirable traits and the level of diversity.Key words: Coconut, genetic diversity, characterization, RAPD, cluster analysis

Application of RAPD markers in hybrid verification in coconut

Abstract -Coconut palms are classified into two majo

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Not AvailableWork on evaluation of coconut germ plasm and hybrids to identify superior lines are in progress at the Central Plantation Crops Research Institute. The present study was undertaken to determine the variability for fruit componenttraits in the conserved coconut germ plasm available at the Central Plantation Crops Research Institute and to determine the association between these traits. A total of 71 coconut accessions, including 58 tall accessions and 13 dwarf accessions were studied for 12 fruit component traits [weight of fruit (g), thickness of husk (em), weight of nut (g), husk wt. (g/nut), percentage of husk, thickness of kernel (em), weight of kernel (g/nut), thickness of shell (em), weight of shell (g/nut), copra content (g/nut), oil percentage, oil content (g/nut)] and two related parameters viz., oil and copra yield/ha. The fruit component analysis indicated wide variability among the coconut accessions for most of the traits studied. The highest CV values were observed for copra yield/ha, oil yield/hectare and weight of nut, respectively. Only oil content in the copra showed a very low C.V of 3.18%, indicating lesser variability for this trait among the accessions studied and also suggesting that oil yield/ha is more influenced by endosperm/copra yield and not by oil percentage per se. Another trait with comparatively lesser CV value was thickness of kernel again indicating that variation in copra/endosperm weight is less influenced by the thickness of the endosperm and is rather determined by the size of the nut. The copra content per nut ranged from 349g in the case of SNRT to 70.40g in the case of SUBD. In general, low copra and oil content was recorded in the dwarf accessions. On the other hand, the large-fruited accessions SNRT, MLT and MVT yielded more than 200ml of oil/nut. The copra and oil yield/ha among the accessions ranged from 0.6-4.46t1haand 0.4-2.94 tlha, respectively. The most inferior accessions were SUBD and the New Caledonian accession NUFT, while the most superior accessions producing more than 4t copra/ha and more than 2.6t oil/ha were FJLT, ADRT, JVT, PHOT and AGT, respectively. The correlation coefficients for the fruit component traits indicated highly significant positive correlation of fruit weight with weight of all the component traits, viz., husk, shell, kernel, copra and oil content per fruit. The thickness of the husk did not show any significant correlation with any of the fruit component traits. On the other hand, the percentage of husk showed significant negative correlation with nut weight kernel weight and copra weight, indicating the need to select accessions with lesser husk percentage while breeding for higher endosperm/oil yield. Copra yield/ha and oil yield/ha showed highly significant positive correlation among themselves, indicating that these are not influenced by the fruit component traits alone and the influence ofannual nut yield on these two traits. Therefore, the fruit weight, husk percentage and nut yield appear to be the most important characters influencing coconut oil output per hectare and hence it is possible to improve coconut oil productivity in the coconut plantations by selection of superior accessions based on these traits.Not Availabl

Bypass of a protein barrier by a replicative DNA helicase

Replicative DNA helicases generally unwind DNA as a single hexamer that encircles and translocates along one strand of the duplex while excluding the complementary strand (known as steric exclusion). By contrast, large T antigen, the replicative DNA helicase of the simian virus 40 (SV40), is reported to function as a pair of stacked hexamers that pumps double-stranded DNA through its central channel while laterally extruding single-stranded DNA. Here we use single-molecule and ensemble assays to show that large T antigen assembled on the SV40 origin unwinds DNA efficiently as a single hexamer that translocates on single-stranded DNA in the 3'-to-5' direction. Unexpectedly, large T antigen unwinds DNA past a DNA–protein crosslink on the translocation strand, suggesting that the large T antigen ring can open to bypass bulky adducts. Together, our data underscore the profound conservation among replicative helicase mechanisms, and reveal a new level of plasticity in the interactions of replicative helicases with DNA damage.