Heterosis for Photosynthesis, Dry Matter Production and Grain Yield in F1 Hybrid Rice (Oryza sativa L.) from Thermo-Sensitive Genic Male Sterile Line Cultivated at Different Soil Nitrogen Levels

Abstract

This study was conducted to determine the effects of soil nitrogen levels (0.22, 0.44 and 0.88gN pot-1) on the heterosis for photosynthetic characters, dry matter production and grain yield in F1 hybrid rice obtained from thermo-sensitive genic male sterile line. Net CO2 exchange rate (CER) and other related characters viz., SPAD reading, leaf N content, soluble protein content and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activity increased significantly with increasing N level in all the F1 hybrid and parental cultivars. With increasing N level, the number of tillers, leaf area, root weight, wholeplant dry weight and grain yield also increased. Under the low N level, the F1 hybrid did not show heterosis for most photosynthetic characters. However, at high N level, heterosis for CER over both the male parent and the mean of parents was ascribed to high leaf N content and several characters related to CER. The F1 hybrid exhibited substantial heterosis over the male parent for whole-plant dry weight, number of panicles per plant, number of spikelets per panicle and grain yield in all N levels. Among the yield components, the strengthening of heterosis for number of filled grains per panicle was the major cause of greater heterosis for grain yield in the F1 hybrid at high N level.