Screening of coconut varieties for tolerance to high temperature stress using pollen viability test
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Date
2016
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Academy of Climate Change Education and Research Vellanikkara
Abstract
Temperature is the major factor that limits the growth and production of coconut
in the humid tropics. Due to the current accelerated climate change, temperature is
expected to rise at the rate of 0.2°C per decade. Coconut pollen, since they have to
stay viable under field conditions from anthesis to pollination, are more vulnerable
to the effects of high temperature. The present study evaluates the impact of high
temperature stress on coconut through in vitro pollen germination technique and
attempts to screen the selected genotypes for tolerance to high temperature stress.
Pollen samples collected from palms belonging to 11 genotypes were allowed to
germinate on an in vitro germination medium containing 8% sucrose and 0.01%
boric acid at the temperatures 20°C, 25°C, 30°C, 35°C and 40°C for a duration of
two hours. Percentage pollen germination and pollen tube length were assessed
after this period. The tall variety WCT had highest percentage germination at all
temperatures, followed by the hybrid COD x WCT. Generally for all genotypes,
germination decreased drastically at 40°C. On an average, COD had much higher
germination than the rest of the dwarf varieties studied, while MYD had the lowest
germination of all the genotypes. Mean pollen tube length also showed a
significantly low value (41.55 μm) at 40°C. Highest mean pollen tube length was
recorded for the hybrid COD x WCT (408.9μm). All talls and hybrids showed
significantly higher pollen tube lengths compared to dwarfs. Optimum temperature
for pollen germination and pollen tube length for all genotypes was calculated. Tall
variety LMT (29.31°C), hybrid MYD x WCT (29.02°C) and dwarf MYD (29.11)
had high optimum temperature for germination. The mean optimum temperature
for pollen germination was 2°C greater than that for pollen tube length. WCT
among talls and COD among dwarfs were found to be tolerant to high temperature
stress.
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