Downward shoot positioning affects water transport in field-grown grapevines.

Grape canopies (cv, Nebbiolo) were manipulated to obtain vines with alternatively upward and downward shoots on the same fruit-cane. Downward orientation reduced length and total leaf area of the shoot and water flow through the shoot, but did not modify shoot water potential. Shoot hydraulic conductivity, either evaluated on growing plants or on cut shoot portions, was lon er in downward than in upward oriented shoots at all positions along the cane, This supports the hypothesis that downward shoot orientation causes a I eduction of the hydraulic conductivity, which in turn reduces the availability of water and nutrients for the leaves growing downstream of the point of conductivity reduction. A mechanism which reduces growth in downward oriented shoots is proposed and practical consequences for viticulture, related to reduced water conductivity in downward-trained shoots, are discussed.