Morphological analysis of leaf and tiller number dynamics of wheat (Triticum aestivum L.): Responses to temperature and light intensity

In recent literature on Gramineae species, leaf and tiller number dynamics have been studied by analysing site filling and the phyllochron of the mainstem. However, site filling is influenced by three components: (1) the phyllochron of the mainstem and daughter tillers; (2) specific site usage (i.e. fraction of buds that ultimately develop into a visible tiller at a specific site); and (3) HS-delay (i.e. difference in Haun Stage (HS) between the parent tiller and daughter tiller above the point where the daughter tiller appears). These three morphological components affecting site filling were studied under different environmental conditions in a growth chamber experiment with spring and winter wheat (Triticum aestivum L.). Treatments were temperature (daily average 10.5, 15.5 or 20.5 degrees C) and light intensity (111, 191 or 286 mu mol m(-2) s(-1)). Effects of temperature and light intensity on phyllochron were well described by equations already reported in the literature. Specific site usage was higher at cooler temperatures and greater light intensities and was related to tiller position. It is proposed that these effects on specific site usage reflect differences in availability of local assimilate for tiller appearance. HS-delay of a tiller was shorter if the expected tiller appearance was later and was only slightly affected by light intensity or temperature. This new concept, combining HS-delay and specific site usage, can be useful in constructing more general models of the effects of environmental factors on the dynamics of leaf number and leaf area of Gramineae species. (C) 1998 Annals of Botany Company.