SHOOT AND ROOT DEVELOPMENT IN RICE RELATED TO THE PHYLLOCHRON

In grasses, construction of a growing plant is determined primarily by the rate of leaf development in the shoot apex and the timing of tillering and rooting of individual phytomers relative to leaf development. Our purpose is to review shoot and root growth in relation to emergence of leaves in rice (Oryza sativa L.). Development of the leaf, tiller bud, and adventitious roots of each phytomer proceeds in order, at a rate that depends on leaf initiation rate at the shoot apex. Consequently, initiation, leaf emergence, tillering, and rooting of each tiller are closely synchronized with leaf emergence on the main stem. Leaves that emerge simultaneously are similar in size. Tillers whose leaf emergence Is retarded from this synchronization will generally die before anthesis. Inflorescence development is closely correlated with development of the subtending leaves in each tiller, resulting in a highly predictable phenology in relation to leaf emergence. Because of these relationships, the leaf number concept provides researchers with an effective index for studying development of shoot and root systems in rice, including the prediction of tiller morphology, the estimation of potential tiller increase, and analysis of root system dynamics.