Oilseed rape (hereafter OSR) contributes a fifth of calories consumed by humans from oilseeds annually. The composition and quality of their lipid-rich seeds is tightly regulated to prevent introducing toxic compounds to the food chain, as these increase in response to environmental stresses such as the phytotoxic pollutant tropospheric ozone. Understanding the effects of ozone on, and potential tolerance mechanisms in, this lucrative crop is necessary to maintain crop quality and yield. Firstly, I investigated the impact of ‘real-world’ ozone levels (20 - 110 ppbv over 12 days to 5 months) on the seed and oil yield of one shorter-lived spring OSR cultivar and one longer-lived winter cultivar to realistic ozone levels over a growing season.
High ozone levels caused differences in seed yield and quality losses, but the winter cultivar’s yield losses were more substantial. I postulated that winter OSR diverted more photosynthate to antioxidants, which protect metabolic processes and prevent damage caused by ozone. I then focused on ascorbic acid, which directly reacts with ozone and stress-inducing products within the leaf and is associated with ozone tolerance. Despite higher concentrations of total ascorbic acid in the leaf, short-term ozone exposure decreased winter OSR physiology and productivity, and cumulative ozone uptake was a key factor in ozone tolerance. I then questioned whether canola-grade cultivars of advanced pedigree and therefore high gas exchange and low antioxidant levels were more sensitive to ozone. Surprisingly, a canola-grade cultivar with the lowest gas exchange and highest antioxidant activity (compared to two non-canola-grade cultivars) was ozone tolerant. I also developed a relative oxidative stress index, which adequately predicted ozone tolerance in the four Brassica oilseeds, which may be applied to identify and exploit Brassica ozone tolerance.
