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U n i v e r s i t y of P e r a d e n i y a

The Institutional Repository of the University of Peradeniya is the University's digital gateway to scholarly knowledge and research excellence. Established as the next phase of the Digital Library initiative launched by the University Library in 2011, it preserves, showcases, and provides open access to the intellectual output of the University community.

Through a rich collection of research articles, conference proceedings, theses, dissertations, and other scholarly works, the repository enhances the visibility, accessibility, and long-term preservation of knowledge, extending the global reach and impact of the University of Peradeniya’s academic and research contributions.

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Identification of edible macroalgae and isolation of macroalgae- endophytes in Hikkaduwa coastal area, Sri Lanka.
(University of Peradeniya, Sri Lanka, 2023-09-20) Arampath, P.C.; Chathuranga, P.H.T.; De Silva, S.
Red, green and brown macroalgae (seaweeds) are the main groups of macroalgae. Some species of macroalgae are well known as a source of food for centuries. Although they are rich in nutrients, their edible uses are unexploited in Sri Lanka. The diversity of macroalgae is prominent in Hikkaduwa coastal area. Endophytes are endosymbiotic organisms associated with antimicrobial, anticancer and anti-insect properties due to their secondary metabolites. These properties of metabolites are important in food and pharmaceutical applications. This research was conducted to identify the edible macroalgae species in Hikkaduwa coastal area and to isolate the endophytes present in macroalgae. Macroalgae were collected with the prior approval of the Department of Coast Conservation and Coastal Resource and the Department of Wildlife Conservation. The collected macroalgae were identified using fresh specimens, photographs, herbarium specimens and available literature. The endophytes study was conducted by culturing them in potato dextrose agar medium after surface disinfection of macroalgae. Identified green algae were Halimeda opuntia, Caulerpa imbricata, Caulerpa racemosa, Ulva lactuca, Valoniopsis pachynema, Valonia utricularis and Chaetomorpha antennina. Identified red algae were Chondracanthus acicularis, Gracilaria canaliculata and Gracilaria huangii. Sargassum elegans, and Sargassum crassifolium were the species identified as brown algae. Macro algae, Halimeda opuntia, Caulerpa racemosa, Gracilaria canaliculata, Ulva lactuca, Sargassum crassifolium and Sargassum elegans species were identified with potential food applications. Growth of endophytes was observed in Gracilaria spp. In conclusion, edible macroalgae and endophytes are existing in Hikkaduwa coastal area. Further research and screening of macroalgae and endophytes are recommended.
Utilization of waste materials to produce silica micro and nanoparticles as a slow release fertilizer
(University of Peradeniya, Sri Lanka, 2023-09-20) Ganehenege, M.Y.U.; Rajapaksha, P.M.G.W.G.; Thomas, M.
Silica nanoparticles (SNPs) are considered as suitable delivery materials considering their unique characteristics. Mesoporocity, large surface area, size variation and manipulative chemical and physical qualities such as hydrophilic or phobic nature, electrostatic charge are some of the important features. SNPs are modified as nanofertilizers, as they can be either controlled release or engineered materials for various functions. However, their physiochemical properties including particle size, pore size, shape and morphology, specific surface area and surface charge, and functionalization can highly affect their adsorption and desorption capacities. In plants, silica is used for both mechanical/physical protection and increased pest tolerance. In this study, silica was selected as the base material to incorporate urea as a nanofertilizer. Silica was extracted from rice husk and coal fly ash under optimized conditions. Six types of silica particles in the size range of 80-400 nm were synthesized from extracted silica using modified template free sol-gel and precipitation methods. Among the six, four were in nanoscale with the particle size <100 nm. The percentage ratio of synthesized silica particles: base material mass ranges from 8 – 48%, based on both the nature of synthesis procedure and the silica source. 1 mg of silica particles revealed 20 mg of urea sorption capacity after simple immersion. In comparison with commercially available urea granules, urea desorption behavior was studied using colorimetric absorption of Urea-Ehrlich’s reagent complex at 425 nm. Variation of production efficiency was observed based on the method and the material. Among the six types of urea adsorbed silica, not only SNPs, but also the silica particles in the 200 nm- 400 nm range showed slow releasing behavior for consecutive 8 day-period regardless of their particle sizes. This may be due to the effect of specific pore sizes, shapes, morphology, specific surface charge and surface area of these particles.
Partitioning of essential and toxic elements between rice (Oryza Sativa L.) grains and husks
(University of Peradeniya, Sri Lanka, 2023-09-20) Manawasinghe, S.; Chandrajith, R.
Rice is the prime source of essential trace elements for consumers as it is a staple food in many countries. However, deficiencies of some trace elements are common among rice-consuming populations. In addition, rice plants have a high potential of accumulating toxic trace elements compared to other cereals, leading to health issues. Such toxic elements can also be taken into the human body by indirect pathways, such as rice husks commonly used as animal feed. This study investigated the partitioning of nutrients and trace elements between rice grain and husk in six traditional and three improved varieties available in Sri Lanka. Acid-digested rice grains and husks were analyzed using an inductively coupled plasma mass spectrometer (ICP-MS). Major elements such as K, Ca, and Na accumulation in rice husks were higher than in grains by 3.4, 2.7, and 7.7 folds, respectively. At the same time, Mg showed comparatively similar values between husks and grains. Essential minor elements such as Zn, Cu, and Mo were evenly distributed between rice grains and husks, while Fe and Mn accumulation was about 4 and 15 folds higher in husks, respectively. These findings suggested that rice husk is likely a sink for essential element accumulation. Toxic trace elements such as Cr and Al showed five folds higher accumulation in rice husks than grains, while Rb and Sr accumulations were 2.5 and 13 folds higher in husks. Accumulation of Mg, Zn, Mn and Al in husk showed significant differences among rice varieties (p<0.05), but there is no significant difference between traditional and improved varieties These findings suggested that rice husks potentially play a significant role in protecting rice grains from bio-accumulation of toxic heavy metals. On the other hand, it may cause essential trace elements deficiency in rice grains.
Developing machine learning models to predict water retention properties of soils of Sri Lanka
(University of Peradeniya, Sri Lanka, 2023-09-20) Vidana Gamage, D.N.; Kasthuri Arachchi, K.A.I.L; Mapa, R.B.
Measuring soil water retention properties, such as volumetric water content (VWC) at field capacity (FC) and permanent wilting point (PWP), is a labor-intensive process, resulting in insufficient data for accurate irrigation scheduling. This study aimed to develop machine learning (ML) models to predict VWC at 10 (VWC10), 33, (VWC33), and 1500 kPa (VWC1500) of Sri Lankan soils using a data set of an extensive soil survey. Soil properties such as soil texture, bulk density (BD), soil organic carbon (SOC) were used with Multiple Linear Regression (MLR), K-Nearest Neighbor (KNN), Random Forest (RF), and Support Vector Regression (SVR) models. The predictive accuracy was evaluated using the coefficient of determination (R2), Mean Absolute Error (MAE), Mean Squared Error (MSE), and Root Mean Square Error (RMSE) across the entire dataset and various textural classes. Among the models tested, MLR outperformed ML models, achieving a satisfactory accuracy (R2 = 0.63) in predicting VWC10 and VWC33 with the sand, silt, and bulk density combination. Furthermore, the combinations of sand and VWC10 and sand and VWC33 notably boosted the predictive accuracy of VWC1500 across all tested models (RMSE 3-4 %), with SVM and RF emerging as the top performers with R2 values of 0.85 and 0.90, respectively. Nevertheless, when silt, SOC, and BD were added to the sand and VWC10 or sand and VWC33 combination, there was only a slight improvement in the predictive accuracy of VWC1500. Results of the study revealed that the SVM and RF could be used to predict the VWC1500 of soils of Sri Lanka with higher accuracy using combinations of easily measured parameters like sand content and VWC10 or sand content and VWC33. Future research will aim to enhance the prediction models for VWC10 and VWC33 by including a larger data set covering diverse soil types.
Isolation and characterization of non-tuberculous mycobacteria (NTM) from freshwater ornamental fish
(University of Peradeniya, Sri Lanka, 2023-09-20) Arulkanthan, A.; Dissanayaka, D.M.S.G.; De S. Jagoda, S.S.S.
Piscine mycobacteriosis is a chronic, systemic bacterial disease of fish caused by nontuberculous mycobacteria (NTM). To investigate the occurrence of different species of mycobacteria in freshwater ornamental fish cultured in Sri Lanka, apparently healthy ornamental fish (family Poeciliidae and Cyprinidae) were collected from selected farms located in the Western, Central, North Central and North Western provinces during the period from January 2016 to February 2018. Visceral tissue (kidney, liver, spleen separately from large fish, as a pooled sample from small fish) and intestinal samples from each fish were subjected to acid-fast stain to detect acid- fast bacteria (AFB) and cultured on Ogawa egg medium for isolation of Mycobacteria. Presumptive mycobacterial cultures were subjected to genetic identification by PCR amplification of 16S rRNA, 16S-23S ITS, rpoB and hsp65 genes. The identity of selected isolates was confirmed by sequence analysis of 16SrRNA gene. Of 442 fish examined from 59 fresh water ornamental fish farms, 99 fish were AFB positive while 343 were AFB negative. A total of 138 fish (31.2%) belonging to seven different species yielded acid-fast positive cultures. Of 187 genetically confirmed Mycobacterium isolates recovered from 138 fish (including multiple isolates from some fish), 96 were identified by 16SrRNA sequencing. The most frequently recovered species was Mycobacterium fortuitum (71%, n = 68/96). Other mycobacteria recovered included species of M. fortuitum group (n=21), M. chelonae-abscessus complex (n=3), M. marinum (n= 2), M. arupense (n=1) and M. houstonense (n=1). Isolation of mycobacteria was significantly high from intestine samples (17.6%: 78/442) than pooled tissues (P<0.05, Chi-square test). It is evident that Mycobacterium is widely prevalent in apparently healthy ornamental fish sampled in this study. Potential risks associated with handling ornamental fish carrying NTM on human health should not be overlooked. Our findings highlight the importance of screening mycobacteriosis in ornamental fish stocks to understand the true prevalence of NTM.