Browsing by Author "Karunanayake, K.O.L.C."

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A disease severity index to monitor stem-end rot development in Mango (cv. Karutha Colomban) and the assessment of pathogenicity of associated pathogens
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Kodituwakku, T.D.; Abeywickrama, K.; Karunanayake, K.O.L.C.
Mango (Mangifera indica L.) is a renowned tropical fruit consumed in Sri Lanka. Significant postharvest losses of mango are caused by diseases which affect the quality of fruits. Stemend rot (SER) of mango is a disease caused by a group of fungal pathogens. Disease severity indices are important for assessing the extent of damage caused by a disease to develop suitable control strategies. An index was developed to evaluate the disease development and the level of severity of SER in mango (cv. Karutha Colomban (KC). Pathogenicity of four fungi isolated from mango with SER was also investigated to find out their contribution for SER development in mango. Four mango fruits (90-days old) washed in tap water followed by sterile distilled water were placed on a plastic tray at room temperature. One selected fruit showing a gradual development of SER was photographed daily. Diseased area of the fruit in each photograph was estimated by DIGIMIZER (Version 5.3.4) software and the disease severity was determined as percentage SER (%SER). An index was prepared using the photographs with percentage SER values. Four fungal pathogens (Lasiodiplodia theobromae, Phomopsis sp., Pestalotiopsis sp. and Xylaria feejeensis) were isolated from mango with SER and their identity was confirmed by PCR using universal primers (ITS1 and ITS4) and DNA sequencing. Healthy mango fruits (90-day old) washed in tap water were surface sterilized with 0.1% sodium hypochlorite and subsequently washed in sterile distilled water. Stem-ends of the fruits were wound inoculated with 7-day old mycelial plugs of each fungal pathogen separately and all four pathogens together. Fresh PDA plugs served as the control. Inoculated fruits were incubated in moist plastic chambers at room temperature for 7 days. Each treatment comprised of four replicates and the experiment was repeated. Percentage SER of each fruit was determined based on the developed index. Mean percentage SER resulted by the combination of all four pathogens and L. theobromae, Pestalotiopsis sp. and X. feejeensis, separately were found to be 67.00 ± 4.77%, 66.75 ± 3.84%, 61.13 ± 3.32% and 60.38 ± 4.58% respectively and there was no significant difference between their pathogenicity (MINITAB 18). The least pathogenicity (16.50 ± 1.66%) was observed in fruits inoculated with Phomopsis sp. and percentage SER of the control was 0.88 ± 0.23% L. theobromae, X. feejeensis and Pestalotiopsis sp. were identified as the major contributors for SER in mango and this may be the first reported evidence in Sri Lanka on X. feejeensis as a potential SER pathogen of mango (cv. KC).
Postharvest Application of Defence Elicitors to Managae Anthracnose In Mango Fruit
(Journal of Science, Faculty of Science, University of Kelaniya, 2019) Karunanayake, K.O.L.C.
The use of defense elicitors; which are agents that stimulate or trigger disease resistance responses in plants have proved to be attractive alternatives to hazardous chemical fungicides in recent years. The present study investigated the possibility of using Salicylic acid and Bion® as postharvest elicitors on mango fruit. Three local mango cultivars were used in the study, ‘Karuthacolomban’, ‘Rata’ and ‘Willard’. Salicylic acid was applied as a postharvest spray at concentrations, 100, 500 or 1000 mg/L and Bion® (Acibenzolar-s-methyl, 500 WG, SYNGENTA) at 25, 50, 100 and 200 mg/L. Disease development following artificial inoculation (10 5 conidia / ml suspension) was assessed. Both elicitors were effective (P<0.05) in controlling postharvest anthracnose. The most effective concentration of SA was 500 mg/L for ‘Rata’, 100 mg/ L for ‘Willard’ and both 100 and 500 mg/L for ‘Karuthacolomban’. In Bion® the most effective concentration was 50 ppm for ‘Rata’ and ‘Willard’ and 25 ppm for ‘Karuthacolomban’. In SA treated fruits the percentage reduction in anthracnose ranged from 40- 77 % while values ranged from 67 – 99% for Bion® treated fruits. Results indicate that both SA and Bion® can be used to control postharvest mango fruit loss due to anthracnose.
Postharvest application of defence elicitors to manage anthracnose in mango Fruit
(Journal of Science of the University of Kelaniya Volume:10, 2019) Karunanayake, K.O.L.C.
The use of defense elicitors; which are agents that stimulate or trigger disease resistance responses in plants have proved to be attractive alternatives to hazardous chemical fungicides in recent years. The present study investigated the possibility of using Salicylic acid and Bion® as postharvest elicitors on mango fruit. Three local mango cultivars were used in the study, ‘Karuthacolomban’, ‘Rata’ and ‘Willard’. Salicylic acid was applied as a postharvest spray at concentrations, 100, 500 or 1000 mg/L and Bion® (Acibenzolar-s-methyl, 500 WG, SYNGENTA) at 25, 50, 100 and 200 mg/L. Disease development following artificial inoculation (10 5 conidia / ml suspension) was assessed. Both elicitors were effective (P<0.05) in controlling postharvest anthracnose. The most effective concentration of SA was 500 mg/L for ‘Rata’, 100 mg/ L for ‘Willard’ and both 100 and 500 mg/L for ‘Karuthacolomban’. In Bion® the most effective concentration was 50 ppm for ‘Rata’ and ‘Willard’ and 25 ppm for ‘Karuthacolomban’. In SA treated fruits the percentage reduction in anthracnose ranged from 40- 77 % while values ranged from 67 – 99% for Bion® treated fruits. Results indicate that both SA and Bion® can be used to control postharvest mango fruit loss due to anthracnose.