Effects of Extreme Heat and Drought on Grapevine Phenology and Varietal Suitability

THE SECOND SURPRISE: PHENOLOGY IS DECOUPLING FROM TEMPERATURE in California. It is becoming more and more difficult to  predict harvest dates as was possible before climate change. How?  Is the decoupling caused by the recent drought conditions in California, or is early bud break caused by asymmetric warming at play?

Climate change poses an unprecedented challenge to agriculture. While growers have always struggled with year-to-year variation in climate – early rains or unusually hot summers – climate change provides a major directional shift in mean climate.
Across the globe, growing regions are warming and plants are shifting in both time and space. Current and future shifts pose a major challenge to researchers and growers alike, yet they also highlight a major avenue to adapt crops to climate change – by understanding and exploiting phenological diversity.

Using winegrapes (Vitis vinifera subsp. vinifera) as a case study, we review the phenological diversity present within one crop and its underlying environmental and genetic drivers. In wine- grapes, harvest dates are strongly tied to temperature, but this sensitivity varies greatly, with differ- ent cultivars (or ‘varieties’) of grapes ripening much more or less for the same amount of warming. This phenological diversity provides a mechanism to help growers adapt winegrapes to shifting climates – by planting different varieties that will grow well under current and future cli- mate regimes. More generally, understanding phenological diversity – including its environmental vs. genetic components – offers a major avenue to use ecological knowledge to advance adaptation for winegrapes, and many other crops, to climate change.