Simulation of wheat ontogenesis. II. Prediction dates of ear emergence and main stem final leaf number

The role of photoperiod in the regulation of wheat development and of the final main stem leaf number was studied on the bass of published data from several laboratory experiments.A procedure was developed to calculate the final leaf number and the date of heading of plants that do not require vernalization.Differences between calculations and field observations were ascribed to an effect of vernalization.Hence a model to predict the final number of leaves and date of heading of a given wheat variety was formulated.The model involves the following assumptions: (1) wheat varieties have different sensitivities to daylength; (2) wheat varieties that require vernalization can be vernalized at a very early stage of growth if sown at the beginning of the coldest period of the year; (3) wheat varieties that are vernalized at a very early stage of growth immedately respond to external photoperiodic conditions; (4) wheat crops sown w i t h a range of sowing dates tend to synchronize time of flowering.It was concluded that if the final main stem leaf number of a crop sown at a given date is known, the date of heading and the correspondmg final number of main stem leaves of every other sowing can be found.The model was validated using field data from 58 experimental tnals performed in the USA and Europe.