Objective Grain-filling, crop yield, and rice quality of the germplasms with long spikes and large grains (LGS) were analyzed for breeding.

Methods Six LGS rice germplasms and the high-quality strong restorer Huzhan were used to determine the production yield affected by the agronomic traits. Accumulation of dry matters in filling grains and crop yield at maturity were measured. Grain-filling process was fitted to the logistic growth equation for a correlation analysis.

Result The logistic growth equation could well predict the dynamic slow-fast-gradual growth pattern of the dry matter accumulation in the developing LGS rice grains. The initial, maximum, and average growth rates, time taken to reach peak filling, effective filling period, and total accumulated dry matters of LGS rice grains were significantly greater than those of Huazhan counterparts. Among the indicators, the grain weight was the highest with the longest time required to reach the peak of CD-4. The correlation coefficients between thousand-grain weight and average rate of the gradually increasing period at the end of development and amounts of accumulation in three periods of LGS rice grains all reached 0.97, while between that and grain count per spike was −0.59 or above. The thousand-grain weight and number of primary branches of LGS plants significantly affected the time to arrive at the maximum growth rate, active filling period, and effective filling period of the grains with a correlation coefficient above ±0.49.

Conclusion The logistic growth equation fitted the process of dry matter accumulation in the grains of LGS rice. The superior to Huazhan grain-filling rate and extended filling duration increased LGS germplasms in accumulating dry matters in grains and ultimately resulted in high production yield of the crop.