Organogenesis and growth of the main culm of wheat from sowing to flowering. I.- Relationships between leaf growth and the differentiation of young leaves or flowers

National audienceThe integrated pattern of growth and development of the main culm of wheat (Triticum aestivurn L.) from germination to heading stage is described. Under controlled conditions with constant temperature, the time between the appearance of two successive leaves was determined early in plant development and remained constant throughout plant development. Similarly, under natural conditions, this time (called thermochrone) remained constant, depending only on the sum of mean daily temperatures (base 0 °C). The activity of the terminal meristems appeared to be strongly influenced by the sub-apical part : during the early stages of growth (juvenile period), the initiation rate of primordia was slow and constant at two primordia per thermochrone ; at the appearance of the first young internodes, the initiation rate increased (transition period) ; when the shoot apical meristem itself became a spikelet (terminal spikelet), the floral progress of spikelet buds returned to a regular rate (floral period). The main features of studying the integrated pattern of wheat morphogenes is are developed