Use of AFRCWHEAT2 to predict the development of main stem and tillers in winter triticale and winter wheat in North East Germany

Winter triticale (cv. Grade) and winter wheat (cv. Taras) were grown in Restock, Germany (54.2 degrees N) for 5 years (1985-91) each with up to four sowing dates. Shoot apex development of the main stem and the two most developed tillers was observed by sampling eight plants every 3-10 days. The developmental submodel of the AFRCWHEAT2 simulation model was tested to predict the developmental events: emergence, start of floral initiation, double ridge, start of floret initiation, end of spikelet initiation and anthesis. Anthesis of main shoots was observed 8 days earlier for triticale than for wheat which was explained by an earlier start of reproductive development in triticale than in wheat. Variation in the dates of phenological events was greater for floral initiation and double ridges than for floret initiation and anthesis in both cereals. Dates of the early stages of development varied more in triticale than in wheat and more for main shoots than for tillers. For both species, standard deviations of the differences between observed and model predicted dates of phenological events were larger among developmental stages than between cultivars. Prediction of the early stages of development (floral initiation and double ridge) was poor for both species. The beginning of floret initiation and anthesis were simulated more accurately. We suggest that progress in simulating the development of cereals is more limited by lack of knowledge about plant physiology, rather than by the process of modelling. Better quantification of the vernalization requirements of different species is identified as an important topic for future work. Developmental parameters calculated for main shoots could also be used to closely predict the development rates of tillers. Differences between the development rates of main shoots and tillers were explained by the weather conditions each tiller group experienced and not by differences in their physiological responses to climatic factors. More research is needed to describe differences in development and vernalization requirements of a tiller when compared with that of a main shoot.