Usefulness of stem dendrometers as continuous indicator of loquat trees water status

• Trunk diameter variations were assessed as water status indicator in loquat trees.
• Irrigated and non-irrigated trees were monitored using stem dendrometers.
• Maximum daily trunk shrinkage did not detect severe plant water stress.
• Water stress had a reducing effect on the maximum trunk diameter evolution of trees.
• The stem water potential was the most sensitivity indicator to water stress.

Postharvest regulated deficit irrigation (RDI) is an effective strategy to hasten flowering and harvest in loquat (Eriobotrya japonica Lindl.) trees, which in the Mediterranean countries has been related to an increase in the economic return. The success of an RDI strategy, however, depends on the duration and severity of the water stress reached by the trees. When RDI is applied, then, it is important to regularly monitor the plant water status. The measurement of the trunk diameter variations by means of stem dendrometers, which can be automated to remotely determine the plant water status, is a proven method for many fruit trees. In loquat, however, its use has not been yet assessed. In this experiment performed in a loquat orchard planted with the cv. ‘Cardona’ during the summer of 2009, the suitability of using stem dendrometers to detect plant water stress was assessed by taking measurements in fully irrigated and trees subjected to a drought cycle of 47 days. Results showed that at the beginning of the drought cycle period there was an increase in the maximum daily trunk shrinkage (MDS) in non-irrigated trees even before that clear differences in stem water potential (Ψs) could be detected between treatments. However, when plant water stress became more severe (Ψs lower than −1.4 MPa), MDS did not increase further. The maximum trunk diameter (MXTD) evolution in control trees showed a steadily increase in trunk growth during the whole experimental period. In non-irrigated trees, however, MXTD remained stable until the end of the treatment when irrigation was resumed. The Ψs was the most sensitive indicator to water stress due to its very low tree-to-tree variability in comparison with the other indicators. Overall results show that trunk diameter variations have some limitations to monitor plant water status in loquat RDI orchards and therefore new alternatives should be explored.