Morphological and physiological traits of large-panicle rice varieties with high filled-grain percentage

Understanding the morphological and physiological traits associated with improved filling efficiency in large-panicle rice varieties is critical to devise strategies for breeding programs and cultivation management practices. Information on such traits, however, remains limited. Two large-panicle varieties with high filled-grain percentage (HF) and two check large-panicle varieties with low filled-grain percentage (LF) were field-grown in 2012 and 2013. The number of spikelets per panicle of HF and LF both exceeded 300, and the filled-grain percentage (%) of HF was approximately 90, while that of LF was approximately 75 over the two years. The results showed that when the values were averaged across two years, HF yielded 12.9 t ha−1, while LF yielded 11.0 t ha−1. HF had a greater leaf area duration, biomass accumulation and transport of carbohydrates stored in the culm to the grains from heading to maturity compared with LF. HF exhibited a higher leaf photosynthetic rate, more green leaves on the culm, and higher root activity during filling phase, especially during the middle and late filling phases, in relative to LF. The length of HF for upper three leaves was significantly higher than that of LF, while the angle of upper three leaves on the main culm was less in both years. Meanwhile, specific leaf weight of HF was significantly higher when compared with LF. In addition, the grain filling characteristics of HF and LF were investigated in our study. Our results suggested that a higher leaf photosynthetic rate and root activity during filling phase, greater biomass accumulation and assimilate transport after heading, and longer, thicker and more erect upper three leaves were important morphological and physiological traits of HF, and these traits could be considered as selection criterion to develop large-panicle varieties with high filled-grain percentage.