Impact assessment of global warming on past changes in coloring of grape berry skins by using a model for estimating berry skin coloring

Abstract

'Kyoho', a leading grape (Vitis labruscana L. × V. vinifera L.) cultivar in Japan, is a black-skinned eating cultivar. The frequency of berries with poor skin coloring, which are called “redly ripening” and have low commercial value, has increased in recent years. We analyzed the influence of past climate shifts in main production areas on the skin coloring of 'Kyoho' grape by using a model for estimating skin coloring from air temperature, to clarify whether recent warming is the cause of the increase in frequency of poor skin coloring. The full-flowering dates of six regions were estimated to have advanced by 3.8-6.1 days owing to the rise of air temperature in April and May. Skin color ratings were estimated to have decreased by 1.1-2.3 (indicating lighter color) and to be lower in warmer regions than in cooler regions. The temperature during the coloring period in cold regions increased owing to both the rise in summer temperatures and the earlier start of the coloring period. According to our model, as temperatures rose from 1971 to 2010, the coloring of 'Kyoho' grape berries in cold regions, where berries with excellent color are now produced, decreased more than in warmer regions.