Abstract:
The present experiment was conducted to determine the impact of accumulated thermal time on the growth, yield
and phenology of Sesame (Sesamum indicum L.) in the dry zone of Sri Lanka. Uma, Malee and MI-3 varieties
were selected and the seeds were sown on three different dates in the 2016 Yala and 2016/2017 Maha seasons. The
experiment was set up according to a two-factor factorial randomized completely block design with three
replicates. Accumulated thermal time was calculated as growing degree days at the vegetative stage, flowering
initiation, 50% of flowering, 100% of flowering and physiological maturity using minimum and maximum daily
temperature. Then the plant height and the number of leaves per plant were plotted against the accumulated
thermal time using the sigmoid growth model. The seed dry weight and dry weight of 1000 seeds were recorded at
maturity. The relationship of plant height and the number of leaves per plant with accumulated growing degree
days (AGDD) was significant for all varieties at different sowing dates in both seasons. The flowering of sesame
initiated at 741 and 713.1 of AGDD in Yala and Maha seasons, respectively. The AGDD needed for 50 % flowering
in the Yala is greater than the Maha season. Full flowering occurred in Maha earlier than the Yala season. Plants
reached physiological maturity early in the Maha season. Seed weight per 15 plants and seed weight per plot were
significantly affected by the interaction between variety and the sowing date in Maha and Yala seasons,
respectively. The highest seed weight per 15 plants was recorded in var. Uma and var. Malee in Yala season while
the highest seed weight per plot was also recorded by var. Uma. Furthermore, 1000 seed weight was greater in
var. Uma than other varieties in both seasons. Sowing seeds early in the season increased seed weight per 15
plants in Yala while seeds per plot and 1000 seed weight in Maha season. According to the results of the present
study, var. Uma could be considered as an efficient sesame variety that performed better when sown early in the
season. Therefore, cultivating var. Uma, early in the seasons might be beneficial in terms of growth and yield in
the dry zone of Sri Lanka. However, further field studies are needed to give a solid recommendation.