Browsing by Author "Perera, H. W. K."

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Development of a potting medium enriched with Acetobacter xylinum, for growing the bush variety of Centella asiatica
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Perera, H. W. K.; Kannangara, B. T. S. D. P.
Plant Growth Promoting Rhizobacteria (PGPR) can enhance plant growth by biological processes. The potential of PGPR in agriculture has steadily increased as it offers an attractive way to replace the use of chemical fertilizers and other growth supplements. Among the PGPR bacteria, Acetobacter xylinum colonizes the rhizosphere of many plants and promotes plant growth through the increased supply of nitrogen during their association with the host plants. The effect of Acetobacter spp. on the growth of maize, sugar cane and sweet potato were studied by conducting many field experiments. The present study was carried out to develop a potting medium enriched with Acetobacter xylinum suitable for vegetative growth of Centella asiatica (Gotu kola) bush variety. A. xylinum strain was grown in Hestrin and Schramm medium and the identity was confirmed by observing morphological and biochemical characteristics. The potting medium (green manure: core dust; 3:1) was collected from the Regional Agricultural Research and Development Centre- Makandura. C. asiatica samples at bedstraw stage were split from mature stage nursery and transplanted in plastic pots containing the prepared potting medium. Two weeks old transplanted samples were distributed into six treatments as control (without treatment) and treated samples containing 103, 105, 107, 109 and 1011 Colony Forming Units (CFUs) of A. xylinum inoculum via soil application in five replications. All treated and control samples were maintained at the plant house, University of Kelaniya. The Kjeldhal digestion method was used to analyze the total nitrogen contents of the medium before and after planting and after harvesting. After 50 days of growth, parameters related to vegetative growth of Gotu kola (number of leaves per bunch, leaf area, chlorophyll content, length of petiole, fresh weight of shoot and root biomass, and dry weight of shoot and root biomass) were measured. The highest mean values for leaf area (10.6 cm2), the chlorophyll content (62.1 %), the length of petiole (14.5 cm), the fresh weight of shoot biomass (9.02 g/plant) and root biomass (1.53 g/plant) and the dry weight of shoot biomass (2.15 g/plant) and root biomass (0.613 g/plant) were obtained for the treated plant sample with 107 CFUs of bacteria, compared to the control. The potting medium with 105 CFUs recorded the significantly higher value of mean total nitrogen content at 50th day after the application of A. xylinum (0.53 %) than the control (0.49 %). The above results demonstrated that A. xylinum has increased the amount of available total nitrogen in the potting medium. Present study indicated that the inoculum size of 107 CFUs of A. xylinum could be successfully used as a bio-fertilizer for a better vegetative growth of C. asiatica.
Isolation and identification of litter decomposing fungi in Nagacholai Forest Reserve, Mullaitivu, Sri Lanka
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Bopitiya, B. D. S. S.; Dewangani, H. G. N.; Perera, H. W. K.; Premachandra, J. A. H. P.; Senevirathna, M. A. T. M.; Kalpani, N. N.; Kodituwakku, T. D.; Kannangara, S.
Nagacholai Forest Reserve, which was disturbed by local terrorism before 2009, is located in Mullaitivu District in the Northern Province of Sri Lanka. It is a tropical dry zone forest, administrated by the Department of Forest Conservation, Sri Lanka. Litter-fall and subsequent nutrient release from decomposing litter are crucial processes that regulate the nutrient availability and the nutrient cycling in soil, as well as the plant growth in forest ecosystems. Litter decomposition rates of forest ecosystems are governed by both biotic and abiotic factors. Therefore, the present study was conducted to study soil characteristics such as pH and electrical conductivity and to isolate and identify the litter decomposing fungi of the Nagacholai forest. Soil and litter were collected randomly by placing 0.5 m X 0.5 m size quadrats on the forest floor. The pH and electrical conductivity of each soil sample were determined by following standard methods. Litter decomposing fungi were isolated from leaf discs (1 mm X 1 mm) obtained from the collected litter following washing and plating method using sterilized distilled water. Pure cultures of isolated fungi were maintained at 28 °C in PDA and morphologically identified using identification keys. The low moisture content in the soil was reflected by brown colour, sandy-podzolic soil. The high proportion of less decomposed, dense litter layer reflected the low decomposition rate due to decelerated soil microbial activity and low water availability. Soil pH was within the range of 6.34 – 6.80 and electrical conductivity at 30 °C varied between 1.23 – 1.57 mS cm-1. Five different fungal species were isolated in high frequencies (50%>) from leaf litter, while four of them were identified up to the genus level based on their vegetative and reproductive morphology (i.e. Mucor sp., Aspergillus sp., Candida sp. and Pestalotiopsis sp.). The remaining unidentified species produced white colour colonies and branched, hyaline, septate hyphae without showing any sexual reproductive structure. Mucor, Aspergillus and Pestalotiopsis are some of the common fungal decomposers found in most of the forests of different climatic zones. However, Candida is a filamentous yeast, which is not frequently reported as a decomposer in terrestrial ecosystems, but found to be a member of the normal soil microflora in forests as secondary sugar fungi. Therefore, Mucor, Aspergillus and Pestalotiopsis could be identified as the most prominent genera of litter decomposing fungi in the Nagacholai forest. Nevertheless, this preliminary study needs to be elaborated further to confirm their identity up to species level using molecular techniques