Agronomic implications of variation in wheat development due to variety, sowing date, site and season

The effect of sowing date on wheat,development was investigated using sever al varieties mt three sites in England during the period 1989-93. Developme ntal stages measured were double ridge, terminal spikelet, flag leaf ear em ergence and anthesis. The duration of the period over which the double ridg e stage occurred was longer than the time from earliest to latest sowing. F or the of her stages the duration was shorter for example in one experiment sowings were made over 70 days but anthesis occurred over a period of eigh t days. There were differences among varieties in the duration of different phases of the life cycle. From September sowings spring varieties generall y developed move quickly than winter varieties, but there were considerable differences in rate of development both among winter and spring varieties. From October and November sowings the response was similar in all varietie s. There were marked differences in development among seasons and sites, ge nerally related to temperature differences. In one season (1992-3) a period of unusually low temperature in October led to rapid early development fro m early sowings. The physiological basis for variation in development and t he implications for exposure to favourable growing periods or environmental hazards are discussed.