Commercially available wheat cultivars are broadly adapted to location and time of sowing in Australia's grain zone

Farmers must choose which cultivar to grow based on the phenology of the cultivar and anticipated season length. The current study investigated the established doctrine of sowing fast maturing cultivars late, and slow maturing cultivars early. This was explored by quantifying the genotype (G) × environment (E) × management (M) available to farmers using commercially released cultivars, where management relates to the time of sowing. Nineteen cultivars of spring wheat (Triticum aestivum) were sown at 3 times of sowing (early, conventional and late) at 13 sites in 2011 and 2012. Sites were located throughout the Australian grain growing region in Queensland, New South Wales, Victoria, South Australia and Western Australia from latitudes 27°34′S to 35°09′S where annual rainfall ranged from 237 mm to 747 mm. In general, the three way interaction between G, E and M for yield was small and cultivar could not overcome the yield penalty associated with a late time of sowing. At 11 of the 13 sites, fast to moderately fast maturing cultivars sown early generated the highest yields. Fast maturing cultivars sown late could not compensate for a late time of sowing. Commercial cultivars were broadly adapted to environment and management, and with these cultivars, the Australian grain growing region could be split into just two environments, south and north. Even then, season appears to be the main arbiter of environment, rather than location per se as individual sites moved from one group to the other, depending on season. There was no evidence to suggest farmers could exploit a cultivar by management interaction for time of sowing with commercial cultivars, as the outcome of the season is unpredictable, and with current technology farmers should simply choose the best performing cultivar for their region and sow it as early as possible.