Browsing by Author "Damunupola, J. W."

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Alleviation of drought stress on immature tea (Camellia sinensis) plants by exogenous application of Abscisic acid (ABA)
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Damayanthi, M. M. N.; Wijeratne, T. L.; Damunupola, J. W.
Phytohormones are chemical substances regulating various physiological and biochemical processes in plants. Abscisic acid (ABA) plays a major role in response to drought stress. This study was done to identify the role of exogenous ABA application in immature tea during progressive drought. The experiment was conducted in a glasshouse at the Tea Research Institute of Sri Lanka, using one-year-old potted tea cultivars, TRI 2025 (drought tolerant) and TRI 2023 (drought susceptible). Plants were brought to field capacity and exposed to a drying cycle by withholding water. When plants achieved moderate moisture stress (volumetric water content around 25% in soil), plants were foliar sprayed with ABA at various concentrations [0 (water-spray – WS), 50, 100, 150 and 200 ppm] along with well-watered (WW - positive control) and no-spray (NS - negative control) treatments. Data were collected at 18 hours and 3, 7, 14 and 21 Days After Spraying (DAS) from randomly selected plants arranged according to Randomized Complete Block Design with 2 blocks and 24 replicate plants per cultivar per treatment. At 21 DAS, plants were re-watered, and the recovery was visually assessed after another 7 days. Physiological and biochemical parameters were measured (9.00 am to 12.30 pm) along with soil moisture content. Maintenance of comparatively a higher relative water content was observed in tea plants treated with 100, 150 and 200 ppm ABA. Although the reduction of gas exchange parameters was initially higher in ABA treated plants, it was significantly lower at later stages with progressive drought. Application of ABA in concentrations of 100 - 200 ppm resulted in comparatively higher photosynthetic rates and stomatal conductance at latter stages (14 DAS and 21 DAS). It was observed that the application of ABA did not improve osmolytes accumulation in tea under drought. At latter stage, 100 - 200 ppm ABA treated plants exhibited comparatively higher total chlorophyll and polyphenolic content in both cultivars compared to NS and WS treatments. Similarly, ABA treatments significantly increased antioxidant activity over NS and WS treatments towards the latter stage of drought. The maintenance of significantly lower dark respiration and higher recovery percentages were also observed in ABA (100 - 200 ppm) sprayed plants. Therefore, it can be concluded that ABA foliar application improves water retention and gas exchange parameters while preserving antioxidant capacity resulting restricted risk of oxidative damage under drought. The exogenous ABA application ameliorates the adverse effects of drought stress and improves drought tolerance in immature tea plants. The levels of 100 - 200 ppm concentration of ABA was better in terms of physiological and biochemical alteration and recovery under drought stress in both tea cultivars. Accordingly, considering the cost factor, the application of 100 ppm ABA can be recommended to use as a potential tool to minimize the drought stress effects in immature tea plants.
Herbicidal properties of invasive alien plants Dillenia suffruticosa and Prosopis juliflora against Brassica juncea and Pennisetum polystachion
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Kaushalya, W. D. D.; Bandara, N. C.; Damunupola, J. W.; Madawala, H. M. S. P.; Jayasuriya, K. M. G. G.; Wijesundara, D. S. A.; Bandara, B. M. R.
Synthetic pesticides can cause deleterious effects on human health and the environment. The rapid spread of invasive alien plants (IAPs) threatens biodiversity and the natural and semi-natural ecosystems. A strategy to address these problems is to develop eco-friendly plant-based pesticides from IAPs. In this study, the two IAPs, Dillenia suffruticosa (Griff.) Martelli. and Prosopis juliflora (Sw.) DC., were evaluated for their herbicidal properties against Brassica juncea (L.) Czern. (Bj) and Pennisetum polystachion (L.) Schult. (Pp). The dry leaf powders of IAPs, were separately extracted into dichloromethane-methanol (1:1) using a bottle extractor. The leaf powders and the concentrated leaf extracts were assayed for their inhibitory effects on seed germination and early seedling growth (shoot length, root length and biomass) of Bj and Pp using a Petri dish assay; 2-methyl-4-chlorophenoxyacetic acid (MCPA) and glufosinate were used as positive controls and distilled water and aqueous dimethyl sulfoxide as negative controls. Each treatment was done on 25 seeds in four replicates, in three trials. The IC50 values of the leaf powders and extracts expressed in equivalent amount of leaf powder for the inhibition of seed germination of Bj and Pp were as follows: 3.70 ± 0.38 and 3.10 ± 0.52 mg cm-2 (D. suffruticosa leaf powder against Bj and Pp, respectively); 1.55 ± 0.05 and 0.23 ± 0.06 mg cm-2 (P. juliflora leaf powder against Bj and Pp, respectively); 1.47 ± 0.07 mg cm-2 (D. suffruticosa leaf extract against Bj); 1.19 ± 0.53 mg cm-2 (P. juliflora leaf extract against Bj). Both IAPs were more effective on Pp than Bj (ANOVA, F = 70, p < 0.001). According to the results of the Kruskal- Wallis test, the leaf powders of P. juliflora (at 3.52 mg cm-2, 2 = 25.7, p < 0.001) and D. suffruticosa (at 17.62 mg cm-2, 2 = 24.3, p < 0.001) and the leaf extracts of P. juliflora (at 5.56 mg cm-2, 2 = 26.2, p < 0.001) and D. suffruticosa (at 8.27 mg cm-2, 2 = 25.6, p < 0.001) displayed more potent inhibitory effects on seed germination than glufosinate (at 4.4 µg cm-2) and MCPA (at 10.6 µg cm-2). Growth parameters of Bj and Pp decreased with increasing concentrations of leaf powders and extracts of IAPs (one-way ANOVA, p < 0.05). The leaves of P. juliflora and D. suffruticosa can be exploited to develop eco-friendly herbicides.
Seed dormancy, germination and soil seed bank composition of 12 common rice weeds of Sri Lanka
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Alahakoon, A. A. C. B.; Abeysiriwardena, D. S. D. Z.; Damunupola, J. W.; Gam-Arachchige, N. S.
Weeds are a major problem that affects rice production causing heavy economic losses. This study was conducted to investigate seed dormancy and germination of common paddy weeds in Sri Lanka and their soil seed bank status. Dormancy and germination of seeds of 12 rice weeds collected from Dambulla area were studied. To test initial seed germination, seeds of each species (five replicates of 20 seeds each) were incubated at 250C in an incubator under 12 hr/12 hr light/dark and 24 hr dark in distilled water and 500 ppm gibberellic acid in Petri dishes containing tissue paper. Final germination percentages were calculated after 28 days. Seeds of species suspected to possess physical dormancy were mechanically scarified prior to germination tests. To study emergence from the soil seed bank, nine soil samples (30×25×10 cm3) from each locality were randomly collected from rice fields representing wet (Peradeniya), intermediate (Kurunegala) and dry (Dambulla and Kekirawa) zones of the country at the beginning of Maha season 2017-2018. Soil samples were spread in plastic trays in a greenhouse and kept continuously moist for three months. Species emerged were identified and the number of individuals from each species were recorded. Data were analyzed using one-way ANOVA. Cyperus difformis and Ludwigia peruviana showed high germination (>80%) in distilled water and can be considered as non-dormant. Seed germination of L . perennis, C . iria, Ischaemum rugosum and Dactyloctenium aegyptium significantly increased in the presence of gibberellic acid indicating the presence of nondeep physiological dormancy (P<0.05). Seeds of Aeschynomene indica germinated only when scarified, confirming the presence of physical dormancy. Isachne globosa, I . rugosum, D . aegyptium and Echinochloa glabrescens showed low germination (<20%) and C . rotundus and Limnocharis flava did not germinate under tested conditions. Germination of six tested species was decreased under 24 hr dark condition. Cyperus iria, C . difformis, I . globosa, L . perennis, L . peruviana and E . glabrescens were recorded in soil samples from all four localities. Cyperus spp. were the most abundant and was significantly higher (P<0.05) in samples collected from the dry zone (>4000 seedlings/m2) than wet and intermediate zones (<1500 seedlings/m2). I . globosa was also higher in samples from the dry zone while Ludwigia spp. were lower compared to the samples from wet and intermediate zones. Information on the seed dormancy type, germination requirements and composition of weed seed banks, will be useful in implimentation of species specific, effective weed control measures.