Modelling phasic development in wheat: a conceptual integration of physiological components

Simulation of phasic development in wheat is necessary in constructing wheat growth and yield models. It is also useful for evaluating cultivar adaptation and scheduling cultural practices. This paper describes a conceptual model of wheat development based on phenological principles, as affected by vernalization, photoperiod, thermal response and intrinsic earliness, and also reports the results of sensitivity analysis and validation of the model. The model predicts when the plant will reach double ridge, terminal spikelet and heading. In the model, the daily thermal sensitivity of development following emergence is determined by an interaction of 'relative vernalization completion' and 'relative photoperiod effectiveness' for that day. After complete vernalization is reached, the daily thermal sensitivity is determined only by relative photoperiod effectiveness, which gradually increases from terminal spikelet to heading. A multiplication between the daily thermal sensitivity and thermal effectiveness generated daily flowering time, which was accumulated to trigger a particular developmental stage. Genotypic differences were characterized as vernalization requirement, photoperiod sensitivity and intrinsic earliness. The model showed a sensitive response to environmental variables of temperature and daylength, and to genetic parameters of vernalization requirement and photoperiod sensitivity. Evaluation of the model using multiple experimental data involving various cultivars and planting dates exhibited a marked goodness of fit between simulation and observation with a root mean square error <5 days. The results indicate that the model can be used as a predictor for the major flowering stages, as well as functioning as a knowledge base for understanding the characteristics of different development components in wheat.