Some progressive steps in coconut research and development in Sri Lanka through utilization of molecular markers

Coconut is the sole species of genus Cocos and as such breeding of coconut is limited to the intra-specific level. Furthermore, the long life cycle, massive stature, highly heterozygous nature, lack of vegetative propagation method, limited number of seeds produced per year and bulkiness of seeds, limit the use of many traditional breeding methods employed in other crops in coconut breeding. Obtaining pure line from heterozygous coconut remained unrealistic because of the long vegetative phase. Thus coconut breeding is confined to mass selection of phenotypically superior parent palms, and to inter and intra-varietal hybridization. All these constraints in coconut breeding make the use of molecular breeding techniques highly attractive. Although identifying molecular markers linked to useful traits and characters to strengthen and fasten the selection and breeding of coconut looks the main goal of using markers, they can be efficiently used for many other applications. This article deals with some other useful applications of molecular markers practically used in the coconut breeding programme in Sri Lanka

Dynamics of ion solvation in a Stockmayer fluid

Molecular dynamics computer simulations were performed to study the dynamics of the ionic solvation in a Stockmayer fluid. The simulations show that the solvent relaxation proceeds in two time regimes. Most of the relaxation occurs in a short time period during which the relaxation process can be described by a gaussian function. The long time regime can be described by an exponential relaxation. The decay exponent of the relaxation function in this regime is the same as the exponent describing the decay of the single dipole correlation function. In addition, the contribution of the rotational and translational modes of the solvent to the energy relaxation was investigated. It was found that when the rotational mode is the dominant mode of the solvent motion the relaxation occurs from the outside-in, in accordance with the Onsager snowball picture. When the influence of the translational mode is increased the Onsager picture breaks down

Structure and dynamics of Cl − (H 2 O) 20 clusters: The effect of the polarizability and the charge of the ion

The effect of the polarizability and the sign of the ionic charge were studied in C1(H2O)20 clusters using molecular dynamics computer simulation technique. From our simulations we concluded that the reduction in the ionic polarizability did not significantly change the structure and dynamics of the Cl - (H20)20 cluster, but the inversion of the sign of the ionic charge produced a large effect. The energetic considerations helped us to understand why CIis located on the surface of the cluster. By being on the surface the anion permits the creation of the hydrogen bonded network between water molecules and that lowers the total energy of the cluster. Simulations with the inverted sign of the ionic charge correspond to that with a hypothetical "Cl + " ion which is similar in size and polarizability to a Cs + ion. The dynamical structures and the quenched structures ofCl + (H20)20 clusters are compared with the idealized structure of the Cs + (HZO)20 cluster proposed recently [A. Selinger and A. W. Castleman, Jr., J. Phys. Chern. 95, 8442 (1991)]

Structures of Cl − (H 2 O) n and F − (H 2 O) n ( n =2,3,...,15) clusters. Molecular dynamics computer simulations

We have performed molecular dynamics calculations on Cl−(H2O) n and F−(H2O) n (n=2,3,...,15) clusters. The calculations show that the F− ion is solvated in these clusters, while Cl− remains attached to the water in the clusters. We also obtained the minimum energy structures for the Cl−(H2O) n and F−(H2O) n (n=6,7,8) clusters. From the comparison of these structures with the dynamical structures we conclude that the solvation of the F− ion is due to the entropy effect

Stabilization energies of Cl − , Br − , and I − ions in water clusters

Molecular dynamics computer simulations were performed on clusters of Cl-(H20)n (n =2, ... ,15). From the simulations we calculated the stabilization energies of the anion in the cluster. These energies were compared with the values of stabilization energies obtained from the photodetachment spectra of X-(H20)n clusters (X=CI-, Br-, or 1-). The comparison confirms the hypothesis that the anion is attached to the water cluster

Cube to cage transitions in (H 2 O) n ( n =12, 16, and 20)

Molecular dynamics computer simulations were performed for (H2O)n (n=12, 16, and 20) followed by systematic quenching under a polarizable and a nonpolarizable model to determine the minimum energy structures each favored. Ab initio calculations were done on several minima for (H2O)12 to determine their relative energies. The polarizable model prefers cagelike structures for all cluster sizes, whereas the nonpolarizable model predicts minima of fused cubes for (H2O)12 and (H2O)16 but makes the transition to a cagelike minimum at (H2O)20

Mobility of stretched water

To study the mobility of stretched SPC/E water and its dependence on temperature and density, five molecular dynamics computer simulation runs were performed. Three runs were performed at temperature 300 K and densities 1.0, 0.9, and 0.8 g/cc. Two more runs were performed at temperature 273 K and densities 1.0 and 0.9 g/cc. At temperature 300 K, the translational diffusion coefficient of the stretched SPC/E water increased with the stretch, at temperature 273 K the translational diffusion decreased with the stretch. This behavior is correlated with the observed changes in the hydrogen bonding pattern of water.To study the mobility of stretched SPC/E water and its dependence on temperature and density, five molecular dynamics computer simulation runs were performed. Three runs were performed at temperature 300 K and densities 1.0, 0.9, and 0.8 g/cc. Two more runs were performed at temperature 273 K and densities 1.0 and 0.9 g/cc. At temperature 300 K, the translational diffusion coefficient of the stretched SPC/E water increased with the stretch, at temperature 273 K the translational diffusion decreased with the stretch. This behavior is correlated with the observed changes in the hydrogen bonding pattern of water

The solvation of Cl − , Br − , and I − in acetonitrile clusters: Photoelectron spectroscopy and molecular dynamics simulations

We present the photoelectron spectra of Cl−, Br−, and I− solvated in acetonitrile clusters (CH3CN) n with n=1–33, 1–40, and 1–55, respectively, taken with 7.9 eV photon energy. Anion–solvent electrostatic stabilization energies are extracted from the measured vertical electron binding energies. The leveling of stabilization energies beyond n=10–12 for the three halides signifies the completion of the first solvation layer. This is different from the behavior of anion–water clusters which probably do not fill the first solvation layer, but rather form surface solvation states. Classical molecular dynamics simulations of halide–acetonitrile clusters reproduce the measured stabilization energies and generate full solvation shells of 11–12, 12, and 12–13 solvent molecules for Cl−, Br−, and I−, respectively. Ordered shell structures with high stability were found for the clusters of Cl−, Br−, and I− with n=9, 9, and 12. This special stability is reflected in the intensity distribution of the clusters in the mass spectra. Larger anion–acetonitrile clusters have the molecules beyond the first solvation layer packed in a small droplet which is attached to the first layer. It is suggested that in general, anions solvated in large clusters of polar solvents, might be located close to their surface

A COMPARISON BETWEEN PLOT AND POINT SAMPLING USING A COMPUTER BASED TREE POPULATION OF Pinus caribaea SRI LANKA

Research was conducted in the University Forest at Yagirala Forest Reserve, KalutaraDistrict, Sri Lanka, to compare the efficiency of point and plot sampling in Pinus caribaeaplantation using computer simulated sampling on a population of trees using data collectedin the field. In all, 3294 trees on 5.4 hectares constitute the population. The data base hasbeen filed with tree number, dbh, X and Y co-ordinates. Edge effect bias was minimizedusing the reflection method.Random sampling was used in all cases for sample sizes n = 10, 20, 30, 60 and 100. Inorder to make meaningful comparisons, the concept of equivalent plot was used whichaimed at obtaining equal tallies per sampling unit for point and plot sampling. Basal areafactors applied were 2, 4, 9 and 16. Efficiency for given point - plot equivalents werebased on standard error % and cost values (where cost was based on time). In 19 of the 20point-plot combinations studied, point sampling was found to be the more efficient. Themost suitable BAF is BAF2 and it is recommended that point sampling be applied inplantation forest inventories in Sri Lanka where trained staff are available.