Native embolism in 'Rocha' pear under different rootstocks and their relationship with plant vigor

Water relation between rootstocks and cultivars is a key issue in pear culture. Studies suggest that the plant water flow may be related to the greater or lesser grafted plant vigor, where an increase in the hydraulic resistance caused by the graft union would lead to plants with lower vigor. The Xyl’em-Plus apparatus was developed to measure the hydraulic conductance of xylem vessels and the embolism in the vascular system of woody plants, which through small segments of plant stems, measures the percentage of loss of conductance (PLC) in the xylem due to air blockage. From this parameter, along with a variable related to plant vigor, such as trunk cross section area (TCSA) increase, we can infer if the hydraulic conductance caused by the rootstock is interfering in the plant development. Thus, this work evaluated the PLC of ‘Rocha’ pear trees, grafted on three different rootstocks, comparing the vigor between these rootstocks with the purpose of inferring the effect of hydraulic conductance on plant vigor. Shoots of ‘Rocha’ pear trees grafted on Pyrus calleryana, ‘BA29’ and ‘EMA’ quinces rootstocks, were collected in an orchard in São Joaquim, SC, Brazil, after fruit harvest. This material was taken to the laboratory to carry out the PLC measurements. PLC and TCSA increase showed significant difference in the different rootstocks. Pyrus calleryana showed the lowest PLC compared to the other rootstocks with the highest TCSA increase, differing significantly from ‘EMA’ for PLC and from both ‘BA29’ and ‘EMA’ for TCSA increase. ‘BA29’ and ‘EMA’ did not present a significant difference between them, in both PLC and TCSA increase. These results show that the xylem water flow restriction in ‘Rocha’ pears is perhaps due to the different characteristics of the rootstocks and related to the lower vigor of pear trees.