Abstract
Six field experiments were conducted in 2008-09 and 2009-10 to compare some morpho- physiological parameters of hybrid and inbred rice in different seasons. Three hybrids along with a modern inbred check were evaluated in each season. Five planting dates for Aman, and four for each of Boro and Aus seasons were selected. The experiments were laid out in split plot design with three replications placing planting dates in the main plots and varieties in the subplots. The parameters such as LAI, CGR, RGR, NAR, PHCGR, light interception at flowering, shoot reserve remobilization, chlorophyll status and photosynthetic rate of flag leaf, source-sink relation, sensitivity of reproductive stage to temperature, grain growth pattern and grain yield of the hybrid and inbred rice varieties were studied comprehensively. Hybrid varieties were out yielded (13-29%) the inbred for their higher spikelets panicle (26%) and higher filled spikelets m2 at early planting in Boro season. And their grain yields were identical in late Boro, early Aus and early Aman seasons. Irrespective of seasons, hybrids had higher LAI, CGR and RGR compared to the inbred before the onset of heading. Spikelets number to leaf area ratio was higher in the test hybrid compared to the inbred. Shoot reserve remobilization to grain at early planting was higher in the hybrids (ca. 18%) in Boro season compared to the inbred (ca. 11%) while reverse scenario was observed in Aman and Aus seasons. Chlorophyll content in the flag leaves was significantly higher in the hybrids over the inbred. Initial flag leaf photosynthetic rate (at 2 DAF) was higher in the hybrids followed by almost similar or even lower than that of the inbred, irrespective of seasons and planting dates. A minimum temperature of 22.5°C during heading stage is critical for spikelets filling in the hybrids. Fluctuation from the minimum temperature (22.5°C) during the reproductive period affected the grain filling severely in the hybrids compared to the inbred. Minimum temperature of 21-23°C is suitable for assimilate transportation and remobilization to the grain in the hybrids. Grain dry matter accumulation from current photosynthate (GDMCPn) to leaf area ratio of the hybrids was similar to the inbred in Aman season and, lower in Boro and Aus seasons. Post-heading growth rates (PHCGR) were almost similar in both hybrid and inbred varieties at Aman and Boro seasons. Accumulated dry matter panicle1 showed higher sensitivity to temperature in the test hybrids compared to the inbred. Photosynthetic capability of the leaf (except flag leaf) was lower in the hybrids than that in inbred at grain filling period. Planting of hybrid rice in 20 December and 05 January in Boro season is optimum for maximum grain yield for exploitation of the agro-climatological conditions of Bangladesh especially minimum temperature (21-23°C) which triggered remobilization of shoot reserves to the grain ensuring higher yield compared to other season and planting dates.