Field and Physiological Performance of ‘Verna’ Lemon on Four Rootstocks Under Semi-Arid Mediterranean Conditions

Rootstock choice can shape orchard establishment and fruit production, but integrated evidence for young ‘Verna’ lemon trees under semi-arid Mediterranean conditions remains limited. Four rootstocks were evaluated for ‘Verna 51’ lemon: Citrus macrophylla (CM), sour orange (NA), Rangpur lime (LR), and Forner-Alcaide No. 5 (FA-5). The trial covered four orchard-establishment seasons (2016–2017 to 2019–2020) in Murcia, south-eastern Spain. Irrigation was scheduled to replace 100% of crop evapotranspiration (ETc). Vegetative growth, yield, fruit quality, midday stem water potential (Ψstem), leaf gas exchange, and foliar mineral composition were assessed in a randomised complete block design. Rootstock affected canopy development, cumulative yield, fruit size, crop water-use efficiency (CWUE), several fruit-quality attributes, and leaf mineral composition. Rootstock effects on Ψstem and gas exchange were detected in 2019, whereas neither intrinsic nor instantaneous leaf water-use efficiency showed a significant overall rootstock effect in either year. CM produced the greatest canopy development and the highest numerical cumulative yield and CWUE; for the latter two variables, CM exceeded LR and FA-5 but did not differ significantly from NA. Overall mean fruit weight was also greater in CM than in NA and FA-5, with LR showing an intermediate value. Fruits from trees grafted onto CM had thicker peel than those from LR and FA-5, lower total soluble solids than those from the other rootstocks, and lower titratable acidity than those from NA and FA-5. FA-5 had the lowest numerical final canopy volume and a lower cumulative yield than CM, whereas NA did not differ significantly from CM in final-season yield and had higher soluble solids and acidity than CM. LR was generally intermediate in growth and production and had a less negative mean Ψstem than FA-5 in 2019. In this young orchard, CM favoured rapid canopy establishment, cumulative production, and fruit size, although these gains were accompanied by less favourable values for some internal fruit-quality attributes.