Abstract:
In Sri Lanka, rice spikelet sterility and poor grain filling capacity have been reported as major
problems in all agroecological zones which are highly dependent on climatic parameters. By
manipulating the transplanting dates of the rice crop, it is possible to manipulate the climatic
conditions that impacted on rice crop in a given time. Therefore, this study was designed to
investigate the effect of different transplanting dates on the grain-filling capacity of rice and thereby
develop an understanding of how climatic parameters contribute towards poor grain filling. This
study was conducted as a field trial at Rice Research Station, Labuduwa using 25 improved rice
varieties adaptable for the Low Country Wet Zone (LCWZ) of Sri Lanka. The experiment was laid as
a Two Factor Factorial Design with two replicates using two different transplanting dates (one-month
intervals in between) during the Yala 2022. Flowering time was set to synchronize with low and high
rainfall intensities by early (P1) and late planting (P2), respectively, based on meteorological data at
Labuduwa, Galle. Agro-morphological diversity of important yield-determining traits was evaluated
at two different transplanting dates and the data were analyzed using analysis of variance. Results
indicated that planting date had a significant effect (p<0.05) on important morphological traits such
as planting height, number of tillers, the weight of panicles, length, and width of roots, dry weight of
roots, number of unfilled grains per panicle, filled seeds percentage and unfilled seeds percentage.
The existence of a difference in filled seed percentage (P1-78.25% and P2-86.3%) at two planting
dates indicated that the transplanting date had a significant impact on the filling capacity of rice
grains. The interaction between variety and planting date was significant (p<0.05) for filled seed
percentage implying that grain filling capacity of rice can be determined by both genetic and
environmental factors. One of the main reasons for changes in the filling capacity of rice could be the
changes in the precipitation pattern, high temperature (29.6oC – 31.5oC) together with high relative
humidity (85%-90%) prevailed during the flowering stage of rice. Relatively low rainfall was received
during the first part of July corresponding to the first transplanting date. These environmental factors
might have affected spikelet fertility during the flowering stage and thereby affect grain filling
capacity. As a way forward, further in-depth studies are required to examine the exact effect of
climatic parameters of LCWZ on spikelet sterility and its impact on rice grain filling capacity.
