The effects of plant growth regulators on winter and spring canola (Brassica napus L.) types in the High Rainfall Zone of south-eastern Australia

European canola cultivars have shown potential to produce high grain yields in the High Rainfall Zone (HRZ) of southern Australia. However these crops grow tall and produce large amounts of non-grain dry matter resulting in harvesting difficulties and inefficiencies in the conversion of resource to grain. Plant growth regulators (PGRs) are a common tool used in the Northern hemisphere to control height, reduce lodging and manipulate the crop canopy to improve light penetration and increase grain yields. An experimental PGR was applied to winter and spring canola cultivars at Hamilton, Victoria in 2010 and 2011 and at Longford, Tasmania in 2011 to determine if crop morphology could be altered to improve grain yields in the HRZ. The grain yield, yield components, crop size and plant architecture of four late maturing European winter cultivars (Taurus, CBI206, CB3 at Hamilton and CBIW208 at Longford) and two mid maturing European spring cultivars (CBI8802 and CBI2610 at Hamilton) were compared with the Australian spring cultivars, Hyola 50 (Hamilton) and 45C75 (Longford). The PGR did in some instances alter flowering and final above ground dry matter (AGDM), pod density, canopy depth and branching and although differences between cultivars and crop maturity were detected, effects were often inconsistent. However changes in plant morphology had no significant affect on grain yield. The lack of yield response was attributed to no lodging in the experiments and the ability of crops in the HRZ to sustain larger canopies than in the Northern Hemisphere without reducing yield. Reducing plant height and improving resource conversion are still important targets in the HRZ and further work needs to be conducted to devise agronomic, chemical and genetic strategies (e.g. through the use of dwarf material) to increase the ease and efficiency of grain production in this environment.