The Syrah cluster on the right was treated with the antitranspirant Vapor Gard; nontreated cluster is on the left. The treated cluster showed slower coloration, a sign of delayed ripening.
PHOTO BY YUN ZHANG
A Washington State University graduate student recently returned from the world’s most prestigious wine university where she collaborated in research on how grape berry water flow influences ripening. Her research highlights the detrimental effects overhead irrigation could have in delaying sugar accumulation and increasing cracking, especially with Concord juice grapes and, to a lesser degree, with Syrah wine grapes.
Doctoral student Yun Zhang spent three months in France analyzing grape berry samples she brought from Washington State. The University of Bordeaux has a specialized molecular biology laboratory designed for genetic work. She received grants and financial support from both WSU and Bordeaux’s Institut des Sciences de Vigne et du Vin (Institute of Vine and Wine Sciences).
Zhang grew up in China and received her bachelor’s degree in agricultural engineering there, studying dams, reservoirs, and canals. She first became interested in wine grapes while conducting irrigation experiments on grapes for her master’s research in China. According to Zhang, grapes are primarily grown in northwest China—raisin and table grapes in the Xinjiang province and wine grapes in the Gansu province, near the ancient silk trade route.
“What’s interesting to me is that Washington State and China’s wine grape regions share similar latitudes and varieties,” she told Good Fruit Grower, adding that Merlot, Cabernet Sauvignon, and other vinifera varieties are grown in China as they are in Washington.
Her grape irrigation research led her to WSU’s Dr. Markus Keller, a horticulturist who specializes in grape physiology. Zhang finished her master’s degree at WSU and will complete her doctorate research of grape berry water relations and their role in berry development later this year.
“Water going into the berry is how we get berry growth and yield, but we tend to forget about how water flows out of the berry and what that means for ripening,” she said.
“Just like in our human bodies, the grape berry has two circulatory systems, the xylem and phloem,” she said.
The xylem is the main pipeline that brings water and nutrients into the grape berry, while the phloem mostly imports water and sugars to the berry. But while the xylem can bring excess water out, the phloem only transports water and sugars into the berry, not out.
The water status of grape berries has a direct relationship to quality and yield, she said. “The net amount of grape berry growth is determined by the balance of the water ins