Grain growth and development of old and modern Australian wheats

Abstract Grain growth of old and modern varieties of Australian wheats was studied in the field to ascertain if any trends in grain growth-rate or duration have occurred in association with breeding for yield. Grains from the mid-ear spikelets of main shoots which had reached anthesis on the same day were sampled frequently for dry-matter. Linear, cubic and logistic functions were fitted to the observed dry-matter data plotted against thermal time. Estimates of grain growth-rate and duration, the time of physiological maturity and the deviation of observed and expected values were compared for each function. The morphological stages of grain development were also recorded in an attempt to identify a character which would provide an easily observed marker for the time of physiological maturity in Australian wheat varieties. The logistic function was found to be the most appropriate model to describe grain-growth in these varieties. The time when maximum grain dry-matter was achieved (physiological maturity) could not be unequivocally identified, but depended on the function fitted to the data. Most modern varieties flowered earlier, had shorter lag phases and longer durations of grain-growth than the older varieties. The final dry-matter of a grain was significantly correlated with maximum growth-rate. Grain-growth rates and maximum grain dry-matter did not demonstrate any trend with the year of release of the varieties. Of the morphological stages examined, the loss of green colour from the glumes and lemma were the most coincident with physiological maturity; however, considerable variation was evident between varieties.