Browsing by Author "Hettiarachi, S."

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Antimicrobial activity of selected spices against Pectobacterium carotovorum isolated from some vegetables in Sri Lanka.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Wasana, W.P.; Kuruppuarachchi, K.A.P.P.; Yapa, P.N.; Hettiarachi, S.
Bacterial soft rot caused by Pectobacterium carotovorum (Erwinia carotovora) is a destructive disease found worldwide, resulting in economic loss. It is important to implement disease control measures and management strategies in order to prevent economic and further crop losses. Antibacterial nature of spices offer promising solutions to pesticidal hazards, environmental pollution, and pesticide residues in crops and to ever increasing cost of plant protection operations. Although there are a number of studies on the antibacterial nature of spices on various pathogens, its effect on Pectobacterium carotovorum is unknown. Therefore, this study was carried out with the objective of determination of the antimicrobial activity of selected spices against Pectobacterium carotovorum. Specific objectives were to determine minimum inhibitory concentration of aqueous and ethanolic extracts of selected spices against Pectobacterium carotovorum. Disease samples of Allium porrum, Solanum tuberosum, Brassica caulorapa, Daucus carota, Allium cepa, Phaseolus vulgaris, Brassica oleracea var. capitata and Raphanus sativus were collected from various geographical regions in Sri Lanka. These samples were transported in an icebox to laboratory at Faculty of Applied Sciences, Rajarata University of Sri Lanka for further experiments. Pectobacterium carotovorum colonies were isolated on MacConkey agar and pure cultures obtained. Different Pectobacterium isolates were identified using physiological, biochemical and pathogenicity tests. The crude aqueous and ethanolic extracts of nine spices, garlic (Allium sativum), garcinia (Garcinia cowa), cinnamon (Cinnamomum verum), tamarind (Tamarindus indica), clove (Syzygium aromaticum), mustard (Brassica nigra), turmeric (Curcuma longa), pepper (Piper nigrum) and ginger (Zingiber officinale)) were prepared with concentrations of 0.005 g/ml to 0.5 g/ml. Extracts were assessed for antibacterial activity by agar well diffusion method. Sodium hypochlorite was used as the positive control while sterilized distilled water and ethanol were used as negative control. The zones of inhibitions were measured after incubation at room temperature for 24 hours. Among the nine spices, only four spices, garlic, garcinia, cinnamon and tamarind were active against P. caratovorum. The largest zone of inhibition was shown by aqueous extract of garlic while the aqueous and ethanolic extracts of cinnamon showed lowest zones of inhibition. The ethanol extract of garlic had the highest diameter of zone of inhibition among ethanolic extracts of spices. There was no significant difference (p>0.05) in inhibition zones between aqueous and ethanol extract of a particular spice. Aqueous and ethanol extracts of clove, ginger, mustard, pepper and turmeric were unable to inhibit the bacterium with the tested concentrations. Minimum inhibitory concentrations of the spices, which inhibited the growth of Pectobactrium were 0.5 g/ml. The 0.5 g/ml aqueous extract of garlic possess an effective antibacterial activity against P. carotovorum and can be used as cost effective and eco-friendly preventive strategy to eliminate P. carotovorum rather than using chemical control methods. Evaluation of antibacterial activity of these extracts in field, is needed before a cost-effective formulation is developed.
Evaluation of entomopathogenic fungi in biocontrol of Aethina tumida (small hive beetle)
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Wijethunga, P.; Hettiarachi, S.; Hettiarachchi, D. K.; Sandaruwan, M. K. D. D.
Small hive beetle (SHB) (Aethina tumida) is considered a scavenger and parasite of honeybees and their colonies especially outside of its native habitats. Larvae of A. tumida consume honeybees’ eggs, broods, pollen, and honey, causing a substantial destruction. To control the beetle, chemical pesticides are commonly used. However, this leads to the emergence of pesticide resistance and this also affects the honeybees as well as and the human health. Therefore, investigation of eco-friendly biological control methods is essential. A. tumida has been recorded recently in Kegalle, Sri Lanka, and this research aimed to evaluate entomopathogenic fungi as potential biological control agents of the beetle. Entomopathogenic fungi species were isolated using two methods: 1. the isolation of fungi from soil using greater wax moth larvae as the bait and 2. the use of natural insect cadavers with visible mycosis. In method 1, larvae were heat treated and placed on soil to prevent excessive webbing. Infected cadavers were placed on PDA containing amoxicillin. Emerging fungi were isolated, purified, and tested for pathogenicity with A. tumida adults and larvae. Treatment groups (n = 20) were tested by dipping for 3 seconds in 108 spore suspension, which was determined by hemocytometer and the control group (n = 20) was tested by dipping for 3 seconds in distilled water. Two out of five fungal species, namely sp1 and sp2, showed 100% mortality of the adults in eight days (p ≤ 0.001). All five fungal species had shown mortality in wandering larvae of the beetle among which four isolated fungal species had shown 100% mortality. Fungal sp1 and sp2 showed 100% mortality from 48 hours (p ≤ 0.001). Further investigations on the identification of fungal species, and the field trials on the control of A. tumida and the effects on non-target organisms are recommended.
In-vitro screening of Punica granatum breeding lines for anthracnose disease resistance by detached leaf inoculation technique
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Ahamath, G. S.; Hettiarachi, S.; Paththinige, S. S.; Thenuwara, T. D. S. L.
The economic losses of Punica granatum cultivation are significantly reduced due to several factors, including anthracnose caused by several Colletotrichum species, notably Colletotrichum gloeosporioides. Primary inoculum disseminated by wind or rain and infects the host using diverse strategies and causes biotrophic and necrotrophic infections. It can lead to significant economic losses in Punica granatum orchards by causing fruit rot, premature fruit drop, and decreased yield. The current study aimed to screen the pathogenicity of Colletotrichum sp. against six new Punica granatum lines to evaluate their level of resistance against anthracnose disease. Detached healthy, young seven leaves of six Punica granatum breeding lines and three varieties were collected for in vitro screening. These leaves were wounded and subjected to drop inoculation with 1 × 105 conidia/ml spore suspension, with five replicates per treatment, one leaf was used as negative control with sterile distilled water drop and one leaf was used as physical control which was repeated thrice. After incubation of inoculated leaves for two days in a moist chamber, leaf and lesion areas were _measured using ImageJ software. Then, the disease severity was calculated as the percentage of infected leaf area over total leaf area, breeding lines were assigned to 1-5 rating scale (0–5% = highly resistance, >5–10% = resistance, >10–25% = moderate resistance, >25–50% = susceptible, >50% highly susceptible). Significance of disease severity among varieties and breeding lines were analyzed by ANOVA and Duncan’s post-hoc test using SAS statistical software. According to the ANOVA test, the effect of variety line on disease severity was significant. Thus there were significant differences in disease severity among the six lines and three varieties (F (8,70) = 4.03, p < 0.0001). Average disease severity percentages of breeding lines, 67, 78, TC11, 46, A1 and A2 were 0% ± 0.00, 2.0% ± 3.99, 4.8% ± 1.81, 15.93% ± 2.49, 24.16% ± 9.69 and 25.76%±13.18, respectively. According to disease severity estimates, 67, 78 and TC11 lines were rated as highly resistant lines and whereas 46, A1 were moderate resistant and A2 was susceptible. Average disease severity percentages of the recommended varieties Nimali, Daya and Kalpitiya hybrid were 4.27% ± 5.76, 4.57% ± 6.84 and 36.18% ± 21.11, respectively. Nimali and Daya varieties were rated as highly resistant varieties and whereas KH was susceptible. Duncan’s Multiple Range Test further identified distinct groups of variety and line based on the disease severity, thus there is no statistically significant difference among the resistance levels of 67, 78 and TC11 new lines and Nimali and Daya varieties and indicate higher resistance to Colletotrichum sp. infection. 46, A1 and A2 new lines have no statistically significant difference among the resistance level and KH variety indicates a significantly higher disease severity compared to all other lines and varieties at α = 0.05. Based on the current study and according to the results Punica granatum breeding lines 67, 78 and TC11 have high level of resistance to Colletotrichum sp. infection causing anthracnose disease.