Studies on the vegetative growth control mechanism of peach (Prunus persica L. Batsch) rootstocks

Tree vegetative growth was investigated on different peach (Prunus persica L. Batsch) rootstocks that have a major influence on tree size and vigor. The research objective was to explain the physiological mechanism regulating vegetative growth among these peach rootstocks using the hypothesis that this mechanism was related to tree water relations. The evidence indicates that peach rootstock effects on tree vegetative growth may be related to differences in tree water status. The first study examined the relationship between water status and vegetative growth among peach trees on different rootstocks. Tree water status was manipulated by partially covering the tree canopy and then evaluating responses in tree vegetative growth. The results showed a direct relationship between water status and vegetative growth of peach trees. This relationship was independent for the different peach rootstocks indicating that tree water status was involved in the mechanism that imparts vegetative growth control by selected peach rootstocks. However there was no clear evidence that the differences in tree water status were intrinsically related to the peach rootstocks. The second study examined the hydraulic architecture of peach trees on different rootstocks. The results showed differences in the hydraulic conductance among the rootstocks. The root system architecture of peach trees on different rootstocks was also examined in this series of experiments. It was observed in the third study that rootstocks have differences in root system morphology which in turn appeared to be related to the differences in rootstock hydraulic architecture. Therefore it was concluded that tree growth potential is moderated by the hydraulic conductance characteristics of the rootstocks used in this study. This was further investigated in a fourth study in which the relationship between rootstock hydraulic conductance and growth was examined by manipulating the hydraulic conductance of trees on different rootstocks. The tree hydraulic conductance was indirectly manipulated by changing the pneumatic pressure conditions of the root system. The results showed a direct relationship between pneumatic pressure and shoot growth of peach trees. This relationship was similar regardless of rootstock, supporting the hypothesis that peach rootstock effects on tree vegetative growth is related to hydraulic limitations of the rootstocks.