Determination of Cultivar Differences of Coconut on Heat Tolerance by In Vitro Pollen Germination
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Date
2013
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
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.
Description
Keywords
Agriculture, Export Agriculture, Crop Production, Coconut