Browsing by Author "Kiriwandeniya, K.G.S."

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    Determination of Cultivar Differences of Coconut on Heat Tolerance by In Vitro Pollen Germination
    (Uva Wellassa University of Sri Lanka, 2013) Kiriwandeniya, K.G.S.; Alwis, L.M.H.R.; Ranasinghe, C.S.
    Coconut as one of the main commercial crops in Sri Lanka, it mainly grows in intermediate zone (around 50% of total land), wet zone (around 25% of total land) and the balance in the dry zone. Heat and drought stress are the main impacts of climate change on coconut production. Therefore, development of heat and drought tolerant coconut cultivars has been recognized as a major adaptation measure to climate change. Plant reproductive organs are more vulnerable to changes in short episodes of stress prior and during early stages of flowering (Ranasinghe et al., 2010). The major cause for failures in pollination under high temperature is reduced pollen germination at temperatures as high as 35 C to 39 C during some seasons. Therefore, it is imperative to develop tools for screening coconut for high temperature tolerance with respect to pollen germination. Several recent studies have used the in-vitro pollen germination and pollen tube growth under different temperatures to screen genotypes for high temperature tolerance. This type of pollen characteristics will provide useful insight into the reproductive tolerance of coconut to anticipated climate change. In-vitro pollen germination and pollen tube growth of typica and nana varieties were studied by Ranasinghe et al., (2010) and suggested that the response of in-vitro pollen germination to temperature will be an accurate method to screen coconut varieties to high temperature tolerance,. Therefore, this study focused on identifying the effect of temperature on pollen germination and pollen tube growth of new coconut hybrids. Methodology Six healthy coconut palms of Tall X Tall (TT), Dwarf Green X Tall (DGT), Tall x San Ramon (TSR), Brown Dwarf x Tall (DBT), Tall x Brown Dwarf (TBD), Brown Dwarf x Sa n Ramon (DBSR), Dwarf Green X San Ramon (DGSR) forms were selected randomly from Raddegoda and Mawathagama sites in Kurunegala, IL1a. The experimental design was Complete Randomized Design (CRD). Male flowers were collected from six palms of each cultivar and pollen of three randomly selected flowers was dusted into microfuge tubes with germination media and allowed to germinate in incubators. Incubators were maintained at predetermined temperatures from 16 C to 39 C within 2 C intervals (3 tubes per temperature regime). Pollen grains were counted for pollen germination (3 slides from each microfuge tube) after 22 hrs of incubation under light microscope. Germination percentage (% PG) was determined. The in- vitro elongation of pollen tubes was measured after 3 hrs of incubation by using an ocular micrometer fitted to the eye-piece of the microscope under a high power (x40). There were 18 pollen tubes per temperature regime for each variety. Maximum pollen germination percentage and pollen tube length recorded after incubation, at each temperature were analyzed using linear and non linear regression models (Ranasinghe et al., 2010). The bilinear equation (Equation 1) was used to estimate cardinal temperatures (Tmin ,Topt and Tmax) of all the varieties. Where; t is actual treatment temperature, and a, b1 and b2: equation constants. Topt: the optimum temperature for pollen germination or tube growth.
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    Determination of Cultivar Differences on Heat Tolerance in Coconut by in Vitro Pollen Germination
    (Uva Wellassa University of Sri Lanka, 2013) Kiriwandeniya, K.G.S.
    Reproductive performance of coconut including pollen germination and pollen tube growth mainly depends on temperature. Therefore, identifying the effect of temperature on pollen germination percentage and pollen tube growth of new coconut cultivars is important to identify the suitable cultivars for heat prone areas. Two experiments were conducted to quantify the response of in vitro pollen germination and pollen tube growth to temperature and to determine the cardinal temperatures (Tmin, Topt and Tmax) for coconut cultivars. New coconut hybrids which are evaluated by the Coconut Research Institute in the intermediate zone (IL 1 a) were used for the study. Pollen was collected from seven hybrids expressing variable tolerance to abiotic stresses. Pollen germination percentage and pollen tube growth were recorded after incubation in artificial growth media under different temperature regimes (16 °C to 39 °C; at 2 °C intervals). The optimum (Tops), maximum (Tmax) and minimum (Tmin) temperatures (cardinal temperatures) for pollen germination and pollen tube growth of different cultivars were analyzed. Cultivars differed greatly for in vitro pollen germination percentage and pollen tube growth with mean values of 61% and 505 tim, respectively. A bilinear and quadratic models best described the response to temperature of pollen germination and pollen tube length. The mean cardinal temperatures (Tmin, Topt and Tmax) averaged over cultivars were 16.7 °C, 28.3 °C and 39.2 °C for pollen germination and 18 °C, 28 °C and 37.7 °C for pollen tube growth. Based on these analyses, cultivars with higher pollen germination percentage and greater pollen tube growth under optimum temperatures and cultivars with higher Topt and Tmax for pollen germination and pollen tube growth can be selected as tolerant to high temperature. It was clear, from this study, that Dwarf x Tall hybrids perform better than Tall x Tall hybrids with respect to in vitro pollen germination and pollen tube growth under high temperatures. Key words- heat stress, pollen germination, pollen tube growth, cardinal temperatures, coconut, fruit set