The vegetative growth phase is characterized by
active tillering, a gradual increase in plant height
and leaf emergence at regular intervals. The length
of this phase primarily determines the growth duration
of cultivars. Some very-early-maturing cultivars
have a shortened vegetative growth phase, while
others have both shortened vegetative and reproductive
growth phases. Panicle initiation (PI; R0 in
the rice growth staging system) may occur before
the maximum tiller number is reached in very-shortseason
and some short-season cultivars. Heading in
these cultivars may be staggered due to later tillers
which produce panicles. In midseason cultivars, the
maximum tiller number is reached and followed by
a vegetative lag phase before panicle initiation