The growth of the rice plant is divided into three phases:
vegetative (germination to panicle initiation);
reproductive (panicle initiation to flowering); and
ripening (flowering to mature grain)
In the tropics, the reproductive phase is about 35 days and the ripening phase is about 30 days.
The differences in growth duration are determined by changes in the length of the vegetative phase.
For example, IR64 which matures in 110 days has a 45-day vegetative phase, whereas IR8 which matures in 130 days has a 65-day vegetative phase.