Effectiveness of peach (Prunus persica) rootstocks for vigor control of plum (P. salicina) scions in relation with xylem vessel size

In Prunus spp., dwarfing rootstocks can decrease shoot growth on scions by causing reduced scion stem water potential compared to the same scion grown on vigorous rootstocks because of their decreased hydraulic conductance which is related to xylem vessel diameter. Preliminary tests of trees with a new sizecontrolling peach rootstock and two plum (P. salicina) scion cultivars indicated that the new peach rootstock was relatively ineffective at controlling the growth of the plum scions. We hypothesized that this may have been due to smaller hydraulic conductance of plum xylem than in peach xylem. The aim of the present work was to determine if there are different xylem anatomical characteristics between two P. persica rootstocks (expressing two different degrees of vigor) and two P. salicina scion cultivars. P. salicina scions had smaller xylem vessels compared to P. persica rootstocks. This led to lower theoretical hydraulic conductances of P. salicina scions compared to P. persica rootstocks. The relationships between the anatomical characteristics of the rootstocks and the scions appear to explain why there were limited vigor differences between the same P. salicina cultivar grafted on different P. persica rootstocks that impart different degrees of vigor to P. persica scions.