Growth and Development of the Wheat Tiller. II. The Dynamics of Tiller Growth

Abstract

From an analysis of the length-time relation for tiller growth in wheat it was concluded that tillers which emerged traced a discontinuous curve, and that the discontinuity marked a critical event in tiller growth. Tiller buds which did not emerge as tillers continued to grow even more slowly, at least until anthesis of the primary shoot. The critical event was identified as that of escape from the cavity in which the bud was tightly contained throughout early development. The timing of vascular differentiation in tiller buds was shown to be size-dependent and there was no evidence for any correlation with the critical event of escape. A strong negative correlation between the lengths of the 3rd tiller buds and their subtending internodes was established, and the presence or absence of the 4th tiller bud was also correlated with its internode length. Current hypotheses relating to apical dominance are reviewed, and it is suggested that the dynamic physical constraints implicit in tiller bud growth add a further complication. It was concluded that hormonal, nutritional and constraint mechanisms need to be integrated as partial mechanisms which interacted at the interfaces between successive levels within apical systems.