Hydraulic conductance of peach trees grafted on rootstocks with differing size-controlling potentials

The objective of this study was to evaluate the hydraulic conductance in various components of peach trees grown on rootstocks with contrasting size-controlling potentials. The experiment was conducted on `Crimson Lady' peach trees grafted onto two rootstocks: a semi-dwarfing rootstock, K-146-44 (P. salicina.3.P. persica hybrid) and a vigorous rootstock, Nemaguard (seed-propagated Prunus persica.3.P. davidiana hybrid). Hydraulic conductance of leaves, stems, trunk, graft union, and root system was measured in the scion/rootstocks with a high-pressure flow meter. Total leaf area and dry-matter partitioning into main tree components were also determined. The above and below ground portions of trees grown on Nemaguard rootstock were 393% and 299% larger, respectively, than trees grown on K-146-44 rootstock. Whether trees were grafted on Nemaguard or K-146-44, the root system accounted for most of the resistance to water flow through the tree. When hydraulic conductance was expressed per unit leaf area, trees on K-146-44 rootstock had significantly lower root conductance than trees on Nemaguard rootstock. Rootstocks had no effect on hydraulic conductance through the scion or the graft union. Trees on K-146-44 also partitioned relatively more dry matter to roots and leaves and less to stems than trees on Nemaguard. The results suggest that high root resistance plays a central role in the dwarfing mechanism induced by the size-controlling rootstock.