Browsing by Author "Jeyaseelan, E.C."

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Identification and in vitro control of pathogen causing leaf spot disease in Centella asiatica in Jaffna peninsula
(International. Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, 2018) Keshiga, A.; Jashothan, P.T.J.; Jeyaseelan, T.C.; Jeyaseelan, E.C.
Centella asiatica is an important medicinal herb that is widely used as a leafy vegetable in several Asian countries including Sri Lanka. Production of C . asiatica has been severely affected by leaf spot disease. The aim of the present study was to identify the pathogen causing leaf spot disease in C . asiatica in Jaffna peninsula and to test the effect of natural extracts on the pathogen. Diseased leaf samples were collected from commercial fields from Valikamam, Vadamarachchi and Thenmarachchi regions and three sites were selected from each region. Symptoms were characterized and pathogen was isolated on potato dextrose agar (PDA) medium following standard procedure. Culture and morphological characters were studied for each isolate. Koch's postulates were carried out to confirm the pathogenicity of the isolates; 10 µl spore suspension (70 spores / µL) was wound inoculated to C . asiatica . This assay was done under greenhouse conditions. Furthermore, extracts of dried root powder of Curcuma longa and fresh leaves of Lawsonia inermis, Azadirachta indica and Vitex negundo were prepared using water and tested for antifungal activity. Leaf lesions were irregular or angular, pale brown to greyish white in the center, and surrounded by dark purplish halo. The lesion had pycnidia, scattered, dark brown to rusty brown, globose and immersed in host tissue. In PDA medium, young cultures appeared white, with fluffy and aerial mycelia and mature cultures appeared to be whitish grey to black with pycnidia. Hyaline in young hyphae turned brown when mature, after two weeks. Chlamydospores were observed in culture . Conidia were formed in the pycnidia. The conidia were initially unicellular, hyaline, ellipsoid to sub-ovoid, turning to dark brown, bi-celled, thick walled and ellipsoid at maturity. Based on the morphological features the fungal isolates were identified as Lasiodiplodia sp. There was no variation among the isolates collected from different regions in Jaffna peninsula. Koch's postulates confirmed the pathogenicity of Lasiodiplodia sp. C . longa water extract (1000 mg/L) significantly reduced mycelial growth and spore germination in vitro . Association of Lasiodiplodia sp. with C . asiatica has not been reported earlier in Sri Lanka. Therefore, this is the first report of leaf spot disease caused by Lasiodiplodia sp. on C . asiatica in Sri Lanka. Further studies are being carried out to identify the pathogen based on molecular techniques.
Okra leaf curl disease: an emerging threat to okra cultivation in Northern Sri Lanka
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Jeyaseelan, E.C.; Sharmya, M.; Jeyaseelan, T.M.; Shaw, M.W.
Okra (Abelmoschus esculentus) is cultivated in tropical, subtropical, and warm temperate regions for its edible fruits. During the last few years okra cultivation in South Asia has been severely affected by okra yellow vein mosaic disease (OYVMD), and several research activities are conducted to find suitable control measures. However, in the last two seasons, okra plants have been affected by a new disease in northern Sri Lanka. The symptoms of the disease coincide with the description of leaf curl disease reported from India. The present study was aimed to quantify incidence of the disease and identify the causative agent associated with the disease in Northern Sri Lanka. Five districts were selected for this study, namely Jaffna, Vavuniya, Mannar, Kilinochchi, and Mullaitivu. In each district, the disease incidence was measured in three different farms affected by the disease. Symptomatic leaf samples and symptomless leaf samples from different plants were collected from each farm. Total DNA was extracted by a modified CTAB method. Polymerase chain reactions (PCR) were carried out using primers specific to begomovirus and its satellites. Leaf samples collected from okra plants grown in insect proof cages were used as control. Seeds of four different okra varieties were tested using PCR with same primers to determine whether the disease could be transmitted via seed. Symptomatic plants showed upward curling of leaves, vein thickening, twisting of the stem and lateral branches with leaves becoming thick and leathery. In the later stages of disease, plants were severely stunted with small, deformed fruit, unfit for marketing. The disease was noticed only in some newly introduced hybrid varieties. Varieties which showed high sensitivity to OYVMD, such as MI5, MI7, TV8 and Haritha, did not show leaf curl symptoms. The disease incidence ranged from 10% to 87.5%. PCR assays confirmed that the disease was associated with a complex of three different viruses: a monopartite begomovirus, betasatellite and alphasatellite. Above viruses were not detected in seeds; therefore, the viruses are unlikely to be transmitted by seeds. The present study has confirmed that some varieties of okra plants are affected by a leaf curl disease in northern Sri Lanka and the disease is associated with infection by a begomovirus and specific satellite viruses. Further studies are being carried out to identify the virus at species level based on nucleotide sequences.