A summary of the effect of high temperature on red grape flavonoid composition and biosynthesis

There is unequivocal evidence that our climate is changing. An increase in mean temperature and in the frequency of extreme heat events has already been reported in Australia (Perkins-Kirkpatrick et al. 2016, Perkins-Kirkpatrick & Pitman 2018), with more record hot weather experienced over the last summer. Maximum temperatures ranged 38-46 degrees C for more than three weeks in January in the Riverina (NSW) and such extremes may occur more often as the climate continues to warm. Temperature increases have been observed in many wine regions around the world and as a consequence, temperature, as an abiotic factor, has drawn increasing research interest worldwide (Bonada and Sadras 2015). Studies initially focused on grapevine physiology and basic grape composition and have in the last 20 years expanded to cover a wide range of primary (sugars, amino acids) and secondary (phenolics) metabolites. This article provides a summary of the effects of high temperature on grape flavonoids, and readers are invited to consult the original publication for more details (Gouot et al. 2019). In the first part, an overview of berry flavonoid metabolism is presented, followed by experimental conditions including phenological stage, duration, intensity, nocturnal and diurnal temperature ranges. In a second part, results of the research conducted over the last decades are compiled and a summary of the sole effect of temperature on flavonoids, e.e. separated from other abiotic factors such as water and light, is provided.