The vascular connections in grafted plants under examination

Aims: Decreasing longevity of vineyards due to the increase in the infection of different grapevine trunk diseases is a growing concern, and could be related to the quality of grafting. The main aim of this study was to evaluate the use of xylem hydraulic conductivity measurements as a potential indicator for the quality of vascular connections in the graft junction of grapevine plants. For that purpose, two specific trials were carried out: (1) the quality of different batches of plants whose subjective quality was previously known from the nursery’s experience was evaluated, and (2) the vascular connections between the rootstock and the scion were evaluated on a different set of plants grafted using different grafting techniques.

Methods and Results: (1) The XYL´EM conductivity meter was used to measure the specific hydraulic conductivity (K_s) of plants from six different batches whose quality was subjectively defined from the nurseryman experience. Hydraulic conductivity was measured in one-year-old dormant plants, which were kept in a cold chamber since leaving the nursery, first on the whole plant, then on the rootstock and finally at the graft junction. Results showed that two of the six batches evaluated had significantly lower values than the others. (2) After reflecting on the previous experience, we decided to perform the measurements in growing plants, for which we used different batches of plants grafted using different techniques but keeping the same scion (Airén) and the same rootstock (110 R) in all of them. The grafting techniques used were ‘omega’, ‘full cleft’, ‘manual whip and tongue’, ‘mechanical whip and tongue’, and ‘V’. This time, K_smeasurements were only carried out on the whole plant by determining the water flow from the scion to the rootstock. Results revealed a tendency that the maWT, meWT and V grafts had higher K_s values than FC or OM grafts, which corresponds to higher growth rates according to results previously collected on a field trial performed on the same type of grafted plants.

Conclusions:

Hydraulic conductivity measurements may be a useful trait for the evaluation of vascular connections between the rootstock and the scion in grapevine.

Significance and Impact of the Study: To the best of our knowledge, there are no similar studies in grapevine combining hydraulics measurements with grafting techniques. Results suggest that the hydraulic functioning at the graft junction could be an interesting tool to measure the quality/quantity of vascular connections on grafted plants, and be used to characterize batches in experimentation or, even, to evaluate batches from the nurseries as a quality control.