Browsing by Author "Kodituwakku, T.D."

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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).
In vitro and in vivo Application of Eco-friendly Treatments to Control Postharvest Stem-end Rot of Naturally Infected Avocado (cv. Pollock)
(The Journal of Agricultural Sciences - Sri Lanka, 2021) Nilmini, R.K.; Kodituwakku, T.D.; Abeywickrama, K.; Kuruppu, M.
Purpose: Stem-end rot (SER) is an endophytic fungal infection of avocado causing significant postharvest losses, affecting its marketability. This study was conducted to identify effective concentrations of selected eco-friendly essential oils and chemicals to control SER pathogens by conducting in vitro bioassays and to develop treatments to control SER in naturally infected avocado (cv. Pollock) using less hazardous alternatives to synthetic fungicides. Research Method: In vitro disc volatilization and poison food bioassays were conducted to identify inhibitory concentrations of some essential oils and chemicals against SER pathogens. Avocado fruits were subjected to eco-friendly fumigation and dip treatments and their pathological, physicochemical and sensory properties were assessed after 7 days of storage at 15 °C. Findings: Disc volatilization bioassay revealed that 5 µL/plate clove oil was most effective against Lasiodiplodia theobromae, Diaporthe nelumbonis and Fusarium oxysporum. According to Poisoned food bioassay, 5% (w/v) sodium bicarbonate and 0.07% (v/v) acetic acid were highly effective against the test pathogens. SER incidence of avocado fruits has been successfully delayed for 7 days after subjecting to fumigation treatment with clove oil and dip treatments with sodium bicarbonate and acetic acid, followed by storage at 15 °C. None of the treatments adversely affected physicochemical and sensory properties of avocado. Originality/Value: Treatments could be further improved by conducting a medium-scale in vivo trial to obtain good quality avocado with higher consumer acceptance.
Morphological and molecular identification of fungi for their association with postharvest fruit rots in some selected citrus species
(2022) Jayasekara, A.; Daranagama, A.; Kodituwakku, T.D.; Abeywickrama, K.
Purpose: The availability of fresh Citrus fruits is limited by their susceptibility to invasion by microbial pathogens which leads to cause serious postharvest losses. The present study was carried out to isolate and morphologically identify postharvest fungal associations from selected Citrus fruit species (C. sinensis, C. limon, C. crenatifolia and C. medica) and to confirm their identity by molecular characterization. Research method: Postharvest fungal associations of selected Citrus fruit species were isolated, and identification was done based on morphological characteristics. Confirmation of fungal associations was done through phylogenetic analysis of newly generated ITS sequencing data. Further, frequency of occurrence of each fungal isolate was calculated in three different districts in Sri Lanka. Findings: From the morphological and molecular identification, Collectrichum fructicola, Collectrichum gloeosporioides, Lasiodiplodia theobromae, Aspergillus niger and Pestalotiopsis sp. were recorded from C. sinensis. Neofusicoccum parvum, Collectrichum gigasporium and Aspergillus clavatus were isolated from C. crenatifolia. Further, Lasiodiplodia theobromae and L. pseudotheobromae were the only fungal association isolated from C. limon and C. medica fruit species, respectively. It is worthwhile noting that this is the first report of association of the C. gigasporium and Pestalotiopsis sp. from Citrus fruits in Sri Lanka. Research limitations: Since this research was mainly focused on the isolation and identification of the potential fungal associations, pathogenicity evaluation could not be carried out. Originality/Value: Findings of potential disease causative agents in citrus will be valuable for agriculture sector, to adopt and practice effective strategies to minimize postharvest losses of citrus fruits.