Browsing by Author "Jayalath, W.G.H."

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Characterization of Agrobacteriu/ll strains from agricultural soils of Bandarawela, Sri Lanka
(First National Symposium of Sri Lanka Association for Mycology and Plant Pathology (SLAMPP), 2019) Somarathna, G.M.T.K.; Somachandra, K.P.; Jayalath, W.G.H.; Attanayake, R.N.
Agrobacterium is a Gram negative, rod shaped, aerobic and motile soil inhabiting bacterium of the family Rhizobiaceae. It is well known as the causative agent of crown gall disease of many plant species around the world. However, not all the Agrobacterium strains are pathcvenic and can cause galls. Only the virulent strains cause crown gall disease on number of plant species and are found only in contaminated soils. These virulent strains of A. tumefaciens harbor Ti plasmids with transfer DNA (T-DNA) region and virulence (vir) genes that are responsible for the pathogenicity. virD2 gene codes for virD2 protein and the endonuclease domain of the virD2 protein cleaves T-DNA border sequences. The ipt gene is the T-DNA borne cytokinin synthesis gene. Therefore, the presence of virD2 gene and ipt gene are useful in identifying pathogenic strains of Agrobacterium. The major objective of this research was to determine whether agricultural soils of Bandarawela were contaminated with virulence strains of A. tumefaciens. Soil samples were collected and bacteria were isolated using soil dilution method, and cultured on Yeast Mannitol Acar supplemented with Congo red and on Yeast Extract Peptone Affar. Five pure cultures of putatively Agrobacterium were further characterized using morphological and biochemical tests including Gram staining, catalase test, citrate utilization test, sugar fermentation test and 3-ketolactose test. These testes were often used for the species level identification of A. tumefaciens. Out of five isolates four were rod shaped with rounded ends and were either single or in pairs. However, the other isolate was in chains and Iono rod shaped. Interestingly, all the isolates were positive for all the biochemical tests. However, these tests do not help differentiating the virulence strains. Molecular characterization of all the soil isolates were carried out using universal 16s rRNA primers and Agrobacterium specific primers targeting virD2 and ipt genes. PCR amplification with virD2 primers successfully amplified the targeted band of 224 bp in all five isolates while ipt produced the expected fragment of about 427 bp in three of the isolates. virD2 cene sequences of selected soil isolates were 100-99% similar to the tumefaciens of the GenBank accession CP032925 and CP032929 reported from Taiwan. According to morphological, biochemical, and molecular Characterization using virD2 and ipt genes it was confirmed that the soil in the inspected field of Bandarawela is contaminated with pathogenic strains of A. tumefaciens. Therefore, farmers should maintain awareness when cultivating susceptible plant varieties in these fields.
Contarinia maculipennis as an emerging threat to Dendrobium in Sri Lanka - A case study.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Dias, M.A.; Amarasinghe, L.D.; Jayalath, W.G.H.; Attanayake, R.N.
Blossom midge, Contarinia maculipennis which belongs to Order Diptera: Family Cecidomyiidae is considered as one of the major threat to ornamental and several crop plant species due to its wide host range. For the first time C. maculipennis was recorded from Dendrobium sp. in 1992 from Florida, but the origin of this species is considered as Southeast Asian region. In Korea, it is officially nominated as a quarantine pest since 2007 due to it’s sever economic impact on vegetable crops and ornamental plants. For the first time in Sri Lanka, completely damaged Dendrobium cultivation was found in an ornamental plant nursery at Gampaha district in 2017. It was noted that the symptoms were similar to that of blossom midge damage. Maggots were found to be feeding inside unopened flower buds, causing deformed, discolored buds and blossoms causing premature bud or blossom drop. Floral buds were often found to be rotted. Samples from immature bud stage to fully opened flowers were randomly collected from infected fields into polythene bags. To identify causative agent, floral buds with larval stages were kept in glass containers to allow them to complete their life cycle and thereby morphological characters were studied to confirm the pest species. In addition, yellow color grease sheets were kept inside the greenhouses to trap any adult stages of the pest species. Samples were collected and preserved using 70% ethanol for identification. Since all the damaged flower buds displayed symptoms of bacterial rots, to determine if any bacterial infection is also associated with the symptoms, bacterial isolation procedure was carried out. Different stages of floral samples were separately surface sterilized for two minutes using 70% ethanol and three serial washings with sterilized distilled water. Tissue macerate was prepared and kept for 3 hours before culturing on Nutrient Agar (NA) plates, Potato Dextrose Agar (PDA) and Luria-Bertani (LB) plates. Each sample had three replicates and ten samples were cultured. Growth from the tissues were observed and pure cultures were obtained. Relative length of the first and second flagellomeres, wing length and pattern, larval sternal spatula and its associated papillae and larval eighth abdominal segments were compared with identification keys which were used to identify the genera, Contarinia. The adult stages of trapped insects and adult stages of insect immerged from the larval stages were useful in confirming the species as C. maculipennis. Basic biochemical tests and Gram’s staining assisted in identifying the bacterium as belonging to the genera, Erwinia sp. and it appears that the bacterial infection occurs as a secondary infection after larval stages of C. maculipennis damage the floral tissues. This is the first record of C. maculipennis infecting orchid nurseries in Sri Lanka and if proper care is not taken it will invade other crop species as the pest has a broad host range. It is not clear whether the pest was a recent introduction through the imports of plant material or whether it is a result of host jump and therefore, it warrants further research.
A preliminary floristic study of Chundikulam forest reserve in Jaffna peninsula
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Ekanayake, G.C.M.; Medhavi, P.I.H.R.; Somasiri, R.P.I.V.; Jayalath, W.G.H.; Siriwardhana, K.H.W.; Samarasinghe, D.G.S.N.; Kannangara, S.
Chundikulam sanctuary is a reserve which is located in the Northern Province, in Jaffna peninsula. This reserve is situated in the dry zone of Sri Lanka and the area consists of mangroves along the shores and scrub lands in the sandy areas. The Jaffna peninsula, including Chundikulam, faced an ecological destruction due to the Sri Lankan civil war which prevailed for almost three decades. Therefore, due to the paucity of data of this arid vegetation, this current study was carried out as the first investigation after war. According to the surveys, Chundikulam covers an area of 19,000 hectares in vegetation. A systematic study on the vegetation of this dry arid zone forest was carried out using randomly selected representative sampling sites to document the vegetative diversity of the region, through a field survey conducted in the peripheral areas of this reserve in March 2016. Five quadrates (10m×10m) per site were placed totaling to 25 random sample collections. Eighteen different plant species were collected during the study and herbarium specimens were prepared and submitted to the Department of Botany herbarium, University of Kelaniya, Sri Lanka. The plant species sampled were trees (8 species), shrubs (4 species) and creepers (6 Species). Among them Carissa spinarum, Borassus flabellifer, Drypetes sepiaria, Stereosperum colais, Prosopis juliflora. Dillenia sp., Pterocarpus sp. were tree species and Atalantia ceylanica,and Memwcylon umbellatum were recorded as shrubs and Euphorbia antiquorum, Jasminum officinale, Hardenbergia sp. were identified as creepers. The dominant plant species of the vegetation was Drypetes sepiaria (Putranjivaceae) while Borassus flabellifer (Arecaceae) was the most abundant.The total vegetation cover was estimated by the mean number of individuals (30.4%). The plant communities that have been recognized in this study within the arid and dry forest in Chundikulam forest reserve will provide preliminary scientific data for a systematic review of the changes in their vegetation after the war which prevailed for almost three decades.