Enhancement of some citrus rootstocks tolerance to drought stress by vermicompost and foliar application of trehalose

ABSTRACT Drought is an important abiotic stressor that restricts agricultural development and yield worldwide. The severity of drought stress is continually rising due to extreme climate change. A field experiment was carried out to evaluate the effects of soil application of vermicompost (V.CO) at 1 kg · plant −1 and foliar application of trehalose (TH) at 10 mM, individually and together, on the growth performance and physiochemical responses of two citrus rootstock seedlings, volkamer lemon ( Citrus volkameriana ) and sour orange ( Citrus aurantium ), under drought stress conditions. Seedlings, 9 months old at the onset of the experiment, were subjected to three irrigation levels: 100% (control), 70% and 40% of field capacity (FC). Results showed that applying V.CO and TH together during moderate drought stress (i.e. 70% FC) significantly enhanced the morphological and biochemical parameters of both citrus rootstock seedlings, including the rootstock height, shoot number, stem diameter, leaf number, leaf area, photosynthetic pigments, antioxidant enzymes and osmotic regulators. Additionally, this treatment reduced the amounts of proline accumulated, percentage of ion leakage, levels of superoxide anions (O 2 • – ) hydrogen peroxide (H 2 O 2 ) and levels of malondialdehyde (MDA) relative to the control seedlings, which were under drought stress but were not treated. Anatomical investigations revealed that drought stress reduced the cuticle thickness, lamina thickness, midrib zone thickness, vascular bundle size of the midrib and mesophyll cell size. However, applying V.CO and/or TH alleviated these effects and caused the anatomical features to improve under stress conditions.These findings suggest that V.CO and TH, especially when applied in combination, are effective strategies for enhancing drought tolerance of citrus rootstock seedlings under water-limited situations.