VERNALIZATION AND PHYLLOCHRON IN WINTER-WHEAT

Phyllochron (degree-days/leaf) has been used to describe phasic leaf development in dynamic wheat (Triticum aestivum L.) crop development models. Vernalization controls the rate of crop development in winter wheat. The objective of this experiment was to determine whether vernalization affected the thermal time required for winter wheat to produce leaves. 'Stephens' winter wheat plants were grown in a controlled environment chamber and in outdoor pots, using both pre-vernalized and non-vernalized germinating seed. In the outdoor pots plants became vernalized naturally and vernalization before sowing had no effect on growth, development, or flowering. In the controlled environment, up to the time of flowering of the vernalized treatment, there were no differences in phyllochron or total leaf number per main stem between the plants seeded using pre-vernalized and non-vernalized germinating seed. The non-vernalized plants continued to produce tillers until the experiment was terminated, however, while tillering ceased at stem elongation in the vernalized plants. These results support the use of a constant value for phyllochron in simulating leaf development in both vernalized and non-vernalized seedling winter wheat plants. However, they also show the need to adequately model the effect of vernalization on development (i.e., the cessation of leaf production and tillering in conjunction with flowering) in order to simulate the development of the crop leaf canopy.