Combined effect of irrigation regime and fruit load on the patterns of trunk-diameter variation of 'Hass' avocado at different phenological periods

- Periodicity of shoot and root growth affects the trunk diameter variation (TDV).
- Fruit load played a dominant role in determining the TDV.
- TDV analyses may provide an integrative “holistic view” of the tree.
- Maximum daily shrinkage cannot be used on an absolute basis for irrigation control.

The objective was to investigate the combined effect of irrigation regime and fruit load on trunk-diameter variation patterns of 'Hass' avocado trees grown in lysimeters, at different phenological periods. Plant water uptake of both fruited and defruited trees was monitored at high temporal resolution during successive growth stages. The trunk growth rate (TGR) during all the experiments was not affected by the irrigation treatments, yet daily TGR fluctuated significantly during the season, probably in association with periodic changes in the priority of partitioning of carbohydrates between reproductive and vegetative plant organs, i.e., flushes of shoot or root growth. Fruit load clearly played a dominant role in determining TGR, very likely because of the dramatic effect of fruit load on stomatal conductance and leaf carbohydrate concentration and, therefore, on the overall availability of assimilates. Thus, analyses of trunk diameter variation (TDV) data that lead to evaluation of TGR and maximum trunk diameter variation (MTDV) reflect phenological stages and periodicity of shoot, fruit and root growth, and also may provide an integrative, “holistic viewpoint” of overall tree status.The observed high dependency between the MTDV and irrigation treatments may indicate that MTDV actually depends on water-stress history rather than on the actual plant-water status. Thus, MTDV cannot be used on an absolute basis for irrigation management control. On the other hand, it may be a very efficient aid to control irrigation when used on a relative basis, after identifying the impacts of local phenological and environmental factors on the MTDV. Furthermore, the immediate MTDV response to accidental faults may illustrate the advantages of using dendrometer devices for remotely controlling irrigation systems.