Browsing by Author "Jayasekera, R."

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Aflatoxigenic Aspergillus flavus and aflatoxin formation in selected spices during storage
(2009) Rajasinghe, M.; Abeywickrama, K.P.; Jayasekera, R.
Proliferation of aflatoxigenic fungi and accumulation of aflatoxins take place during storage of spices at various environmental conditions. The objective of this research was to identify the aflatoxigenic fungal species and their aflatoxin forming potential in selected spices during storage in the laboratory and refrigerator. Dilution series of spice samples namely chilli (Capsicum annum) powder, curry powder, turmeric (Curcurma longa) powder and pepper (Piper nigrum) powder (purchased from two producers) were prepared separately and the frequency of occurrence of aflatoxigenic and other fungi were assessed after plating each on Potato Dextrose Agar and incubating at ambient temperature. Aflatoxin formation of A. flavus was confirmed by growing a pure culture on a SMKY medium and identifying toxins on thin layer chromatographic plates. The presence of aflatoxins in spice samples stored at 30 ± 20C and 40C was also confirmed. Long storage of spices leads to aflatoxin production irrespective of storage temperature hence, it is advisable to consume spices such as chilli powerder, tumeric etc. within a relatively short period to avoid build up of aflatoxins.
Air pollution monitoring at the Environmental Specimen Bank of Germany: spruce and pine shoots as bioindicators
(Springer-Verlag, 1996) Rossbach, M.; Jayasekera, R.
An investigation has been carried out to study the pattern of heavy metal abundance in buds, needles, twigs and cones from single trees and to compare the results with the integrated (composite, homogenized) ESB material of the same origin. It has been evident that (i) pine and spruce shoots are comparable in terms of the pattern of trace element abundance with the exception of Ni, Ba, Sr and Pb, (ii) twigs contribute substantially to the overall concentration of the homogeneous material, and (iii) heavy metal concentrations are remarkably different in samples from remote and industrialized sampling sites. To distinguish the influence of soil at different sampling sites on the overall concentration levels, an extensive investigation using chemometrical data evaluation has still to be carried out.
Background levels of heavy metals in plants of different taxonomic groups from a montane rain forest in Sri Lanka
(Kluwer Academic Publishers, 1996) Jayasekera, R.; Rossbach, M.
An undisturbed natural reserve area iocated in a tropical montane rain forest at about 1800 m altitude in Sri Lanka served as a study site to investigate and assess the natural background concentration levels of As, Cd, Co, Cu, Ni, Pb and Zn in plants representing different taxonomic groups (divisions) in the plant kingdom. The plants selected were: the lichen,Usnea barbata (old man's beard);Pogonatum sp. (a moss);Lycopodium selago (epiphytic lycopod);Polypodium lanceolatum (epiphytic fern);Bulbophyllum elliae (epiphytic orchid) andActinodaphne ambigua(dicotyledonous large tree). Degree of homogeneity with respect to Cd, Cu, Pb and Zn in homogenised materials of all samples were within acceptable limits, whereasPogonatum sp. showed the highest degree of homogeneity for Pb. In addition to confirming extremely low levels of heavy metals in all plant species, the survey also found that generally the primitive plants,UsneaandPogonatum appear to have a greater tendency to accumulate As, Cd, Co and Pb; in particular,U. barbata appears to be an efficient accumulator for those heavy metals, suggesting its potential use in environmental studies.Actinodaphne ambigua was found to have a specific accumulating ability for nickel. Surface cleaning of theA. ambigua leaves resulted in a substantial decrease in the foliar contents of Cd, Ni, Pb and Zn. Variations in heavy metal contents observed in different plant genera are discussed in terms of their habits and place of growth in the forest. It is anticipated that the background levels presented in this paper from a remote, unpolluted tropical ecosystem will provide useful reference data for comparative environmental studies.
Bulk and trace element analysis of spices. The applicability of k0-standardization and energy dispersive Xray fluorescence
(Elsevier, 2004) Jayasekera, R.; Freitas, M.C.; Araújo, M.F.
Methodology has been developed for the bulk and trace element analysis of spices such as curry powder and turmeric powder originated from Sri Lanka by the k0-standardization method (INAA-k0) and by energy dispersive X-ray fluorescence (EDXRF). SRM 1572 citrus leaves was used to check the accuracy of the results obtained by the two nuclear techniques. The elements determined quantitatively in these matrices by the EDXRF analysis were bromine, calcium, copper, iron, potassium, magnesium, manganese, phosphorus, rubidium, sulphur, strontium and zinc. The results obtained by the two techniques are comparable, although a few inconsistencies were detected, requiring adequate attention for their correction, whenever possible, in future studies.
Chemical composition of the mangrove, Rhizophora mangle L.
(Elsevier, 1991) Jayasekera, R.
Enrichment and deposition of selected minerals in mangrove, Rhizophora mangle, plants grown under glasshouse conditions at near-constant salinity were investigated. The results show that R. mangle is capable of concentrating a variety of chemical elements by taking them up from salt water. Mean concentration factors for elements found in R. mangle lie in a higher range compared with those of a glycophyte, Brassica oleracea. Moreover, R. mangle plants seem to have higher affinities for elements such as sodium (Na), chlorine (CI), silicon (Si), cobalt (Co) and cerium (Ce), which may or may not be essential to them.
Concentration levels of major and trace elements in rice from Sri Lanka as determined by the k0-standardization method
(Humana Press, 2005) Jayasekera, R.; Freitas, M.C.
Instrumental neutron activation (INAA) with k 0 standardization has been used to determine the concentration levels of a variety of major and trace elements (Al, As, Br, Cd, Cl, Co, Cr, Cs, Cu, Fe, Hg, K, La, Mg, Mn, Mo, Na, Rb, Sc, Se, and Zn) in rice grains (raw and parboiled) and in rice flour collected from local markets in Sri Lanka. In addition, the energy-dispersive X-ray fluorescence (EDXRF) analysis has been used to determine the three elements Ca, P, and S in powdered samples. To evaluate and assure the accuracy and precision of the k 0 standardization method, the IAEA standard reference material V-8 rye flour was analyzed. The results obtained in the present investigation were compared with the results reported from other countries. All of the elements detected in the rice matrices from Sri Lanka were very low in concentration or within normal limits for food plants. Approximate daily dietary intakes of the individual elements supplied through rice were calculated and compared with the available literature values of daily allowances.
Development of a Job Control System to Optimize Web Traffics
(2007) Fernando, S.; Dalugama, J.; Jayasekera, R.; Dassanayake, G.; Patu, V.; Minato, A.; Ozawa, S.
Effect of available rooting volume on seedling growth
(Springer-Netherlands, 1993) Jayasekera, R.; Lieth, H.
During the early establishment phase of Rhizophora mangle L. seedlings, a consistent positive relationship between available soil volume (varying from 2-91) and growth rate of Rhizophora manglehas been established under greenhouse conditions. As soil volume increased, root systems were larger and consistently less dense. From the results obtained it may be concluded that for optimal growth of Rhizophora mangle seedlings, the volume of soil per plant should approach that volume associated with the growth of the plants in natural habitats. Root volume appears to be a very significant index of plant growth, even under saline, flooded conditions.
Effect of poultry manure and inorganic fertilizer on the arbuscular mycorrhiza in coconut
(National Science Foundation of Sri Lanka, 2009) Karunasinghe, T.G.; Fernando, W.C.; Jayasekera, R.
Elemental composition of different plant species
(Journal of Plant Nutrition, 1987) Markert, B.; Jayasekera, R.
Element concentrations in leaves and needles of different plant species (Rhizophora mangle, Astertri‐polium, Vaccinium vitis—idaea and Pinus sylvestris) are presented in the form of element concentration cadasters with reference to their abundance. The concentration cadasters of the two halophytes (Rhizophoramangle and Aster tripolium) show that the elements Na, Cl, Br and Sr occur at high concentrations in halophytes. The changes in chemical abundances of halophytes can be attributed to the extreme habitat conditions, i. e. physiological drought, under which they grow. Certain elements are preferentially accumulated in specific plants, e. g. Mn in Vaccinium vitis‐idaea.
Elemental concentrations in a tropical montane rain forest in Sri Lanka
(Kluwer Academic Publishers, 1992) Jayasekera, R.
As a preliminary to studies on biogeochemistry of a tropical montane rain forest at about 1800 m altitude in Sri Lanka, the concentrations of 17 chemical elements in different forest compartments, i.e. in leaves of six floristically dominant tree species, undergrowth, litter, and soil at 0–10 cm and 11–60 cm depth were determined. Foliar chemical differences between species were large. Mean leaf water content, mean leaf area per leaf, and specific leaf weight of each species were also determined. Calcium seems to be used in relatively large quantities by these plants. Phosphorus concentration in all compartments was consistently low. A few species investigated appeared to concentrate aluminium and silicon at high amounts. Concentration differences between compartments were significant only for certain elements. Location effect on the concentrations in soil was considerable for most of the elements studied. When studying plant-soil chemical interactions in these forests, species-level concentrations must be taken into account as the species-specific chemical differences are obscured when treated as canopy leaves.
Environmental specimen banking: a new concept for environmental monitoring and assessment
(University of Kelaniya, 1992) Jayasekera, R.
A Family with alkaptonuria showing quasidominant inheritance
(Sri Lanka Medical Association, 1999) de Silva, A.P.; Seneviratne, S.L.; Gunatilake, S.B.; Fonseka, M.M.D.; Jayasekera, R.; de Silva, H.J.
No Abstract Available
The Impact of Analysts’ Stock Recommendations on the Hong Kong Stock Market
(Department of Accountancy, Faculty of Commerce and Management Studies, University of Kelaniya, Sri Lanka, 2016) Choudhry, T.; Nandi, M.; Jayasekera, R.; Dassanayaka, G.; Vigne, S.
Analysts’ recommendations play an important role in providing significant information to market participants in the stock market. This paper examines the short-term price impact of analysts’ recommendations (upgrades, downgrades and initiations) on major stocks in the Hong Kong stock market from 2009 to 2014. Our findings show that on average, recommendation upgrades convey substantial and permanent information to the market and result in significantly positive abnormal returns. On the other hand, recommendation downgrades generate even larger price impacts surrounding the announcement day. This implies that recommendation downgrades deliver more significant information to the stock market than upgrades. Our results provide evidence in favour of the markets’ significant reaction to predictions from stock analysts during and after the announcement day taking into account market conditions.
Implementation of specimen banking concepts in developing countries: First trial - Sri Lanka
(Elsevier, 1993) Jayasekera, R.; Rossbach, M.
The necessity to establish a small scale Environmental Specimen Bank projects in tropical countries is stressed. An example from Sri Lanka demonstrates the needs, the benefits and the prospects of such an integrated research project.
Improvement of Text-based E-learning Contents by Using a New Multimedia-type Web Authoring Tool - A case study from a Sri Lankan University
(2007) Dassanayake, G.; Patu, V.; Fernando, S.; Jayasekera, R.; Minato, A.; Noguchi, H.; Ozawa, S.
Interelement correlations in the mangrove, Rhizophora mangle L.
(Springer-Netherlands, 1993) Jayasekera, R.; Lieth, H.
Assuming linear relationships between elements, some significant interelement relationships were detected in Rhizophora mangle grown over a salinity gradient. Sodium (Na) had a clear antagonistic effect on the uptake of potassium (K), whereas the uptake of chromium (Cr) and arsenic (As) seemed to be stimulated by sodium ions. A positive relationship between leaf carbon content and sodium concentration was also found. A significant negative correlation was found between the chemically related two elements, rubidium (Rb) and caesium (Cs). Owing to the competition with the absorption of K+ and NH+ 4 a negative relationship between nitrogen (N) and potassium (K) was found.
Interelement relationships in leaves of tropical montane trees
(Kluwer Academic Publishers, 1993) Jayasekera, R.
Chemical concentrations in leaves are reported for 14 elements in 6 tree species of a montane rain forest in Sri Lanka. The plant taxa varied greatly in chemistry and a few taxa appeared to concentrate several elements in high amounts. The chemical variability among taxonomic units was examined by comparing element-by-element concentration ratios in leaves. Several species seemed to have typical patterns of concentration ratios for certain elements and the interelement relationships of different species seemed to be repeated across varying habitat conditions.
Interspecific Relationships of Piper Species in Sri Lanka as Revealed by DNA Barcode ITS
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Jayarathna, N.; Senanayake, S.P.; Rajapakse, S.; Jayasekera, R.; Paranagama, P.A.
The genus Piper which is the largest genus in the family Piperaceae is economically important as it comprises with valuable crop species as well as several wild species. Although ten species of genus Piper are recorded in Sri Lanka, their interspecific relationships were not well studied. Therefore, the aim of this study was to determine interspecific relationships of Piper species in Sri Lanka using internal transcribed spacers from nuclear ribosomal DNA )ITS(. Ten varieties of Piper nigrum L., two varieties of each P. betle L.and P. longum L., P. chuvya )Miq.( C. DC., P. siriboa L., P. sylvestre Lam., P. walkeri Miq. and P. zeylanicum Miq. were used for the study. The genomic DNA was extracted from tender leaf samples using CTAB method, PCR amplified using ITS primer pair and subjected to DNA sequencing. The DNA sequence alignment analysis was carried out and a dendrogram was constructed using the multiple sequence alignment programme MUSCLE. According to the dendrogram clear formation of two major clusters can be seen and ten P. nigrum varieties were clustered together however, variety Kuching has shown a separation from the main cluster. P. longum, P. walkeri, P. sylvestre, P. siriboa, P. betle, P. chuvya and P. zeylanicum formed the other cluster in which P. siriboa has shared close similarities with P. betle, while P. sylvestre and P. walkeri displayed close relationships and clustered together with P. longum varieties. Interspecific relationships between wild species and cultivated species )P. nigrum, P. betle and P. longum( indicated the potential of using the wild species in breeding programs for crop improvement. However, further studies to reveal genetic and phenetic relatedness of those species are needed to deepen the knowledge on interspecific relationships of Piper species.
Large scale air monitoring: Biological indicators vs. air particulate matter
(2000) Rossbach, M.; Jayasekera, R.; Kniewald, G.