Potential yield benefits from increased vernalisation requirement of canola in Southern Australia

Long season, winter-type canola cultivars have the potential for significantly higher yields than short-season, spring-type canola, yet until recently, breeding of new canola cultivars in Australia has focussed on spring-type canola. This has been to accommodate the typically drier, warmer conditions across the Australian cropping belt where long-season varieties do not perform well due to delayed flowering and risk of water-stress during grain fill. However, as cropping continues to expand into the Australian High Rainfall Zone (500–900 mm, HRZ), breeders have become increasingly interested in developing winter-spring crosses (not yet commercially available) which have an intermediate phenology between that of a spring and winter-type canola. As the vernalisation requirement for these crosses is lower than winter-type canola, the areas where such cultivars can be grown profitably in Australia is potentially much wider than for winter-type canola. Field experimentation and crop simulation studies across the potential cropping region of southern Australia were used to determine the yield potential of these winter-spring canola crosses compared with currently available spring-type and winter-type cultivars. Our analysis showed that the four winter-spring crosses evaluated had a range of vernalisation requirements which were between the small requirements of spring-types and the large requirement of winter-types. In this study the Catchment Analysis Tool (CAT) spatial modelling framework was used to determine the expected canola yields of four cultivars across the entire cropping region of southern Australia. These cultivars were the spring-type 45Y88CL, winter-type Hyola^® 970CL and two winter-spring crosses K50057 and K50058 with vernalisation requirements at the higher end and the lower end of the range of winter-spring crosses, respectively.

The potential benefit of some increase in the vernalisation requirement, based on the area currently sown to canola, was an additional 381 M tonnes per year (based on 50-year average) of canola, if K50058 was sown in areas where it proved superior to 45Y88CL. At the 5-year average canola price of $486 t⁻¹, this would provide an additional AUD 185 Mil/annum for the industry. In general, the modelled yield advantage from canola cultivars with increased vernalisation requirement was greater in the areas of southern Australia that had milder climates and higher rainfall. The value to the Australian canola industry of substituting spring cultivars (e.g. 45Y88CL) with winter x spring (K50057) or winter (Hyola970CL) cultivars where they had a yield advantage, was AUD 82.8 M and AUD 29.2 M, respectively.