Comparing regional risks in producing turnip rape and oilseed rape – Impacts of climate change and breeding

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Summer turnip rape (Brassica rapa L.) is the dominant oilseed crop in Finland. It has lower production risks compared with summer oilseed rape (Brassica napus L.). However, climate-change-induced increases in temperature accumulation could favour oilseed rape and, hence, the relative importance of the two crops could be reversed in the future. This study compared production risks associated with turnip rape and oilseed rape in two climate-change scenarios, the high-emission A2 scenario and the low-emission B1 scenario, with or without changes in the length of the growing season. To compute future changes in temperature accumulation, observations were modified by the average of temperature increases simulated by 19 global climate models. Four plant-breeding scenarios were also included: a similar pace of yield improvements as recorded over recent years, halved or doubled rates of improvement, and no improvements (levelling off). The production risks were compared by analysing the yield-value changes under projected conditions (i.e., in different combinations of scenarios) on the basis of temperature- and plant-breeding-dependent changes in seed yield, oil content, and chlorophyll content. Both plant breeding and climate change already have alone the potential to change the balance between oilseed rape and turnip rape. When acting together the change will be more apparent and faster, but plant breeding will, however, play a more significant role in yield-trend changes than will climate change under northern conditions. If the current rate of plant-breeding improvements continues, only a 100°C increase in temperature sum during the growing season would result in domination of oilseed rape over turnip rape in Finland. This comparative analysis also indicated that strategies, including doubling of oilseed crop production area, are realistic if the climate change and plant breeding achievements facilitate cultivation of oilseed crops in more northern areas. If northern areas are taken into oilseed crop production the lifespan of turnip rape in Finnish field crop production could be extended. Nevertheless, a breeding strategy for northern conditions needs increased efforts focussed on oilseed rape.