Abstract
A pot experiment was conducted to investigate the presence of heterosis for photosynthetic and morphological characters at the active tillering, heading and dough-ripe stages in five F1 rice (Oryza sativa L.) hybrids produced by crossing a thermo-sensitive genic male sterile (TGMS) line with indica and japonica cultivars. CO2 exchange rate (CER) in single leaf and some other photosynthetic characters viz., SPAD reading (a parameter of chlorophyll content) and leaf nitrogen (N) content were lower in most F1 hybrids than in their respective male parents during the growing season. A positive correlation of CER with SPAD reading and leaf N content was observed in the F1 hybrids and parent cultivars at all the growth stages. Specific leaf area (SLA) in most F1 hybrids was higher than that in the parent cultivars, and it was negatively correlated with CER. All the F1 hybrids showed a significantly positive heterosis over both the male parents and the mid-parents for the number of tillers, leaf area, root dry weight and dry matter accumulation per plant at all the growth stages. It is considered that the positive heterosis for dry matter accumulation was mainly due to the larger number of the tillers and lager leaf area per plant at the early stage of development. The improved development of the root system at the early stages also contributed to heterosis for dry matter production in the F1 hybrids.
