Sour orange rootstock increases water productivity in deficit irrigated 'Verna' lemon trees compared with Citrus macrophylla

The response to a regulated deficit irrigation (RDI) strategy was evaluated in trees of 'Verna' lemon grafted on two rootstocks with different vigour. The experiment was carried out during three consecutive years in the IMIDA experimental orchard located in Torre Pacheco (Murcia, Spain), using 8-year-old trees of 'Verna 51' lemon grafted on Citrus macrophylla Wester (CM) and sour orange (Citrus aurantium L.) (SO). The tree spacing was 4 × 5 m and irrigation was applied through one drip line per tree row, with four self-compensated drippers (4 L h−1) per tree. Two irrigation treatments were applied: Control (100% ETc) and RDI. The RDI trees were fully irrigated (100% ETc) along the season except in two fruit growth periods, phase I (cell division) and phase III (ripening and harvest), the irrigation applied being 25% ETc. The main results show that fully-irrigated trees on CM had better plant water status and greater efficiency of water use, which led to higher pruning weight and yield than on SO. With respect to fruit quality, CM fruits had higher juice content, while the fruits from SO trees had higher total soluble solids (TSS). However, under RDI the responses of the rootstocks differed. The water deficit imposed during the stress periods affected much more the plant water status of trees on SO than that of trees on CM, but the pruning weight decreased much more in CM trees than in SO trees. The RDI also affected the accumulated yield much more in CM trees (which suffered a 28% decrease) than in SO trees, which maintained values similar to those of the control. Fruit quality was affected by the RDI treatment similarly in the two rootstocks, with both the titratable acidity and TSS increasing. Thus, based on these results, we recommend the use of the CM rootstock for 'Verna' lemon trees grown in regions where the available water resources are not limiting, due to its higher vigour. However, we recommend the use of the SO rootstock when the water availability is not assured, due to its higher water stress tolerance.