PURSE 2013

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https://ir.lib.pdn.ac.lk/handle/20.500.14444/59

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Browsing PURSE 2013 by Author "Ahangama, D."

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    Evaluation of different prune cut protectants for management of low country live- wood termite of tea
    (The University of Peradeniya, 2013-07-04) Bandara, G. K. T. P.; Mohotti, K. M.; Ahangama, D.
    The Low Country Live-Wood Termite (Glyptotermes dilatatus) is considered as the most economically important major pest of low-country tea in Sri Lanka. Chemical control of the pest has proved to be ineffective and uneconomical. Instead, the use of tolerant cultivars, sanitary pruning and application of wound dressings to prune cuts are recommended in the Integrated Pest Management strategy. As a persistent and cost effective wound dressing is a timely need for the industry, eight alternative wound dressings were screened for preventing wood rotting and safeguarding the tea bush from the pest under laboratory and field conditions using G. dilatatus on the susceptible cultivar TRI 2026. Candarsan (existing recommendation), Brunolium 15%, Brunolium 3%, their Wax mixtures and Enamel Paint were evaluated as prune cut protectants by checking fungal colonies growing on the cut surfaces. Missing parts were observed in cuttings treated with Candarsan under laboratory and field conditions, and in highest persistency than other prune cut wound dressings over the two month period. Therefore, Brunolium 15% can be considered as a cost effective wound dressing with antifungal properties and field persistency.
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    Evaluation of methods for cultivar screening against shot-hole borer (Xyleborus fornicatus Eichhoff.)in tea
    (The university of Perdeniya, 2013-07-04) Hemachandra, P. A. I. U.; Mohotti, K. M.; Ahangama, D.
    Shot-hole borer (SHB) (Xyleborus fornicatus Eichhoff.) in tea is the most important pest causing economic damage at nursery, young and mature stages resulting in poor establishment, direct yield loss and long term bush debilitation. The existing cultivar screening method against SHB using the econventional tray method possesses several limitations with inconsistent results. Therefore, this study compared four cultivar screening methods with the conventional tray method to determine the differential susceptibility of tea cultivars to SHB. The screening methods compared were: (a) bioassay using glass jars; (b) bioassay using olfactometric principles; (c) development of borer populations in artificial diet media prepared using tea bark extractions and (d) using nursery tea plants under natural borer infestations in the field . Seventeen TRI cultivars (TRI 4078, 4071, 4053, 4052, 4046, 4042, 4014, 4006, 3072, 3063, 3025, 3019, 3018, 2043, 2025, 2023 and 777) and six estate selections (DN, DG39, DG7, CY9, DT1 and PK2) with known tolerance or susceptibility to the pest were evaluated. The tested cultivars behaved in a similar manner with respect to the mean number of galleries with a correlation coefficient of 0.24 (p=0.0008) between the conventional method and glass jar bioassay, whereas it was 0.056 (p=0.4523) between the conventional method and the olfactometric method. The mean number of Shot-hole borers was not significantly different (p <0.0001) among the tested cultivars in artificial diet media. The results of cluster analysis comparing mean number of galleries of the tested cultivars with known standard tolerant and susceptible cultivars, TRI 2023 and TRI 2025 too supported the above findings except those from the olfactometric method. Based on an overall comparison of the tested methods in terms of cultivar behavior, easiness, efficiency and time taken, in vitro testing of stem pieces using glass jars bioassay was found to be the most appropriate method for cultivar screening against the SHB. As screening under natural infestation in the field gave differential ratings of tolerance against the pest, further studies with additional physiological measurements are proposed.
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    Mortality of five populations of the burrowing nematode, radopholus similis in aqueous and soil media under different temperatures in vitro
    (The university of Peradeniya, 2013-07-04) Tennakoon, T. M. C. H.; Mohotti, K. M.; Ahangama, D.; Amarasena, P. G. D. S.
    The Burrowing Nematode, Radopholus similis is the second important root damaging nematode pest of tea in the mid- and low elevations in Sri Lanka. The nematode incidence is governed predominantly by soil temperature and rainfall. The survival and population dynamics of R. similis are favored by soil temperatures between 24° and 30°C while high soil moisture contents hinder population growth. In recent years, R. similis has been diminishing in its original locations while establishing in new areas despite integrated nematode management methods. This has been attributed to possible climate change experienced in the different tea growing areas. In this study, adult and live R. similis collected from Nawalapitiya, Deniyaya, Kanneliya, Morawaka and Hapugastenna were exposed to 24°C, 28°C and 30°C temperatures. Mortality of mature nematodes in aqueous and soil media under controlled conditions was studied in vitro. Amongst the nematode sources, the Nawalapitiya population was highly sensitive to temperature which showed 66.6% and 84.6% mortality at 30°C in aqueous (p=0.0054) and soil media (p=0.0031) respectively. In contrast, the Kanneliya population showed the lowest mortality percentages at temperatures 28° and 30°C although they were not significantly different from that at 24°C in the two media (p=0.2967 in aqueous medium and p=0.234 in soil medium). A significant variation of mortality percentages at 30°C was demonstrated by Deniyaya, Hapugastenna and Morawaka populations, compared to the mortality percentage at 24°C in the soil medium. In contrast, nematode mortality in the aqueous medium did not vary significantly with soil temperature. Despite mortality differences observed in the different R. similis populations, higher survival at increased temperature was probably due to better adaptation to changes in soil temperature. Field samplings of the present study showed the emergence and disappearance of nematode levels in under changing climate. These results highlight the need to develop adequate mitigation specific nematode management strategies. Furthermore, these results highlight the potential of harnessing nematodes as an indicator species in investigating the impacts of climate change in agriculture.