Scions influence apparent transpiration efficiency of Vitis vinifera (cv Shiraz) rather than rootstocks.

Carbon isotope discrimination (') is used to determine differences in apparent transpiration efficiency amongst genotypes of many C3 plant species. In this present study the possible influence of certain commercially-available rootstocks on apparent transpiration efficiency in grapevines was investigated. Variation in ' was studied for Shiraz and each of six rootstock varieties when grown either (1) on their own roots, (2) with Shiraz grafted as a scion onto different rootstocks (conventional graft) or (3) with rootstock varieties grafted onto Shiraz roots (reciprocal graft). When grown on own roots or as a reciprocal graft, there was significant variation in '. In contrast, there was no significant variation in ' for Shiraz (as a scion variety) when grafted onto different rootstock varieties (conventional graft). These results imply a predominance by the scion genotype in determining variation in the leaf-level physiological characteristics that determine apparent transpiration efficiency under well-watered (and non-saline) conditions.