Effect of different planting times on grain filling capacity of rice (Oryza sativa L.) in low country wet zone of Sri Lanka

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.