Joelle Bou Harb* and Markus Keller
*IAREC, Washington State University, 24106 N Bunn Road, Prosser, WA 99350, 235 Canyon Drive, Prosser, WA 99350 (joelle.bouharb@wsu.edu)

Varieties of Vitis vinifera L. differ in their response to water availability. The attempt to classify varieties into the two categories of isohydric and anisohydric responses has produced much discrepancy among trials. We hypothesize that this is due to the lack of consideration for a biological continuum across varieties rather than the adoption of two extremes. Our goal was to study 18 V. vinifera varieties under the same environmental conditions. We imposed dry-down/recovery cycles and explored the behavior of the varieties over the full soil moisture range in 2015, 2016, and 2017. We used eight replicate vines per variety to measure midday leaf water potential and stomatal conductance, as well as soil moisture. Our results show that there may be three distinctive major patterns of midday leaf water potential response to soil water availability: Linear drop across the entire soil moisture range, linear drop below a threshold of soil water content, and a plateau reached at a soil moisture threshold. Meanwhile, the stomatal sensitivity often did not mirror the midday leaf water potential behavior; i.e., varieties with tight control of water status often had stomata insensitive to soil moisture depletion, while some varieties with a linear drop of water status had tight stomatal control. As transpiration is affected by vapor pressure deficit, some varieties showed a response to this parameter under high soil moisture, while other did not. These results may eventually be used by growers in irrigation management decisions.

Funding Support: Washington State Grape and Wine Research Program WSU