Co-ordination of leaf emergence and leaf and spikelet primordium initiation in wheat

Abstract

Abstract Leaf emergence and primordium initiation were measured in experiments done with different varieties in a wide range of environments. Leaf initiation, relative to leaf emergence, proceeded at a constant rate. After initiation of the first spikelet, the rate of primodium initiation (primordia per emerged leaf) changed to a faster, approximately constant, rate which was maintained until initiation of the terminal spikelet. Rate of leaf initiation (1.7 primordia per emerged leaf) was similar in all cases analysed. Rate of spikelet initiation varied from about 3.5 to 7 primordia per emerged leaf, and was negatively correlated with total number of leaves on the shoot, which varied from 7 to 14. A rectangular hyperbola describes the relation between rate of spikelet initiation and total number of leaves. The analysis shows that there is a metrical relationship between different elements of shoot development. A model is given which shows how ear initiation and stem elongation are modulated in shoots with differing total numbers of leaves. The relation between leaf emergence and primordium initiation suggests control of apex development by emerging leaves, or vice versa. An accumulation of growing leaves may regulate growth and development of the shoot apex.