Yield potential and radiation use efficiency of super hybrid rice grown under subtropical conditions

China's super hybrid rice breeding project has developed many new varieties using a combination of the ideotype approach and intersubspecific heterosis. It is controversial whether these super hybrid varieties have increased the yield potential of irrigated rice. This study was conducted to compare grain yield and yield attributes among super hybrid, ordinary hybrid, and inbred varieties. Field experiments were done in Liuyang (moderate-yielding site) and Guidong (high-yielding site) counties. Hunan Province, China, in 2007 and 2008. Two varieties from each varietal group were grown in each field experiment under moderate and high N rates. Grain yield, yield components, aboveground total dry weight, harvest index, total N uptake, and crop radiation use efficiency (RUE) were measured for each variety. A significant difference in grain yield was observed among the varieties and varietal groups but not between the two N rates. super hybrid varieties have increased rice yield potential by 12% compared with ordinary hybrid and inbred varieties. The higher grain yield of super hybrid varieties was attributed to improvement in both source and sink. super hybrid varieties produced more biomass than ordinary hybrid and inbred varieties. Long growth duration and high accumulated incident radiation were partially responsible for high biomass production for the super hybrid varieties. super hybrid varieties had significantly larger panicle size (spikelets per panicle) than ordinary hybrid and inbred varieties, which resulted in larger sink size (spikelets per m(2)). Crop RUE did not explain the yield superiority of super hybrid rice. Our study suggests that super hybrid rice varieties do not necessarily require more N fertilizer to produce high grain yield. (C) 2009 Elsevier B.V. All rights reserved.