Analysis of Grain Yield Formation Components of Extra Heavy-Panicle-Type Mid-Season Indica Hybrid Rice

Rice is the most important food crop species of the developing world, and there are increasing concerns about food security to increase rice yields significantly. A 2-year field experiment was conducted in Chongqing, China, to evaluate differences in the characteristics of yield-related biomass accumulation and transport for extraheavy-panicle-type rice (ET), heavy-panicle-type rice (HT), and medium-panicle-type rice (MT) by measuring the biomass yield increase of different organs and total increase per stem of these rice types at all growth stages after booting. On the basis of the characteristics of yield-related biomass accumulation and transport, ET showed significantly higher biomass yield and harvest index than HT and MT did. There were significant positive correlations between biomass yield, harvest index and panicle weight of the analyzed rice cultivars. The higher biomass yield of ET was attributed to leaf area duration (LAD) and specific leaf weight duration (SLWD), which were significantly higher than those of HT and MT, and to leaf drooping angle duration (LDAD), which was significantly lower than that of HT and MT after the milking stage (MS). LDAD was more effective than LAD or SLWD for characterizing biomass yield. The relatively high harvest index of ET was due to the output amount (OA), output rate (OR) and transformation rate (TR) of photosynthate in the stems after the MS, and these values were significantly higher than those for HT and MT. TR was more effective than OA or OR of the stems for characterizing the harvest index. Thus, we believe that the LDAD of functional leaves and TR of photosynthate in the stems after the MS can be considered key indices for breeding ET cultivars in the future.