Abstract
The duration of the maturity phase, time from heading to the optimum harvest time after grain growth ceased, is important for rice productivity. However, little is known about the determinants for cultivar differences in the duration of the maturity phase due to difficulty of determining the optimum harvest time non-subjectively. The objective of this study was to develop a method for measuring the spikelet yellowing ratio, which is an index of optimum harvest time, by image analysis, and to elucidate the determinants for cultivar differences in the duration of the maturity phase. The relationship between grain number, grain weight, and ripening period was analyzed using ‘Koshihikari’ and its near isogenic lines (NILs) with different numbers of spikelets; and ‘Yamadawara’ and ‘Emidawara’, which have similar genetic backgrounds but differ in duration of maturity phase. The results showed that the number of grains was not always the determining factor in the duration of maturity phase. On the other hand, the analysis of each panicle revealed that the increase in grain weight almost completely ceased when spikelet yellowing began. Furthermore, the duration of the maturity phase was more strongly correlated with the lag time from the end of grain weight increase to maturity, than the duration of grain weight increase. These results suggested that this lag time may also be a determinant for the duration of the maturity phase.
