Objective Amylose accumulation during grain filling stage of rice varieties with varied amylose content was studied to decipher the starch synthesis mechanism for improved eating quality or processing performance by breeding.

Method Waxy and two varieties of rice with high or medium amylose content were selected to monitor the changes on the dry matter, amylose accumulation and content in the grains during filling stage. The Logistic equation was used to fit and analyze the amylose accumulation.

Results As rice grains developed and maturing, dry matter and amylose increased in a slow-fast-slow pattern. The 3 different varieties accumulated dry matter similarly in the manner of gradual incline, steep increase, then slow rise to reach a stabilized level. However, the time required to reach the maximum level varied from 15 d to 27 d. The Logistic equation could significantly predict the amylose accumulation of all 3 varieties at fitting coefficients (R²) of 0.967-0.998. The accumulation rate peaked at 7-9 d after anthesis which meant a shortened grain filling duration and an early arrival of maximum filling. It took 14-22 d after anthesis for a gain to arrive at the peak accumulation on amylose and 15-27 d on dry matter. Both rate and amount directly related to the amylose content in a grain. The high amylose rice variety had greater amylose synthesis ability with higher accumulation rate from the early filling stage than the low amylose varieties.

Conclusion The model of Logistic function satisfactorily predicted the amylose accumulation of a rice grain. High amylose content tended to require longer time for the accumulation, unless the rice variety was highly efficient in amylose synthesis.