Silicon (Si) is the second most abundant element in the Earth’s crust. It is a nonessential element for plant growth, but it is considered beneficial because it can prevent biotic and abiotic stresses. Because nothing is known about the effects of Si in the olive, two experiments were performed with young plants of ‘Arbequina’ and ‘Picual’ cultivars to evaluate the effect of continuous Si applications on the incidence of olive leaf spot, the main foliar disease affecting this crop. Plants were grown in pots containing a mixture of washed sand and peat. In the first experiment, Si was foliar sprayed (foliar treatment) or applied to the soil through irrigation water (soil treatment) at the concentrations of 0, 2.5, 5, and 10 or 0, 1.25, 2.5, and 5 mg·L−1, respectively. The treatments were arranged in a completely randomized design for each cultivar. In the second experiment, the experimental design was a randomized complete block design in a 2 × 4 factorial arrangement, consisting of two forms of Si application (foliar vs. soil) and four concentrations (0, 5, 10, or 20 mg·L−1). Leaf Si concentration significantly increased with the amount of Si applied. After 5 months of treatments, plants were inoculated with a conidial suspension of the pathogen, and the disease index (DSI) was calculated. Shoot growth only increased in ‘Picual’ after Si application. The DSI showed a significant reduction in both cultivars treated with Si when compared with control plants, although differences between cultivars were observed.

Water deficit in young fruit trees can reduce growth and future orchard productivity. Exogenous silicon (Si) applications have been associated with induced resistance to biotic and abiotic stresses such as water deficit, but the role of Si in fruit trees is still largely unexplored. The aim of the study was to evaluate the effect of Si applications on water status and gas exchange of young peach trees. This study comprises two experiments arranged in a factorial design with two water regimens (well-irrigated or water-stressed) and three Si concentrations (0, 10, or 20 mg⋅L−1 in the first experiment; 0, 20, or 40 mg⋅L−1 in the second experiment). Si applications via foliar spray were performed weekly after the water regimens were clearly established. Tree water status (midday stem water potential), and gas exchange parameters (CO2 assimilation, leaf transpiration, stomatal conductance, leaf water use efficiency) were measured. Si application at 10 or 20 mg⋅L−1 improved water status of water-stressed trees without affecting gas exchange, but 40 mg⋅L−1 reduced CO2 assimilation. Thus, foliar applications of Si could be a promising strategy for nonirrigated, nonbearing orchards to maintain their water status during dry periods and/or improve their recovery from water deficit.

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Silicon (Si) is a nonessential element for plant growth, but it influences the tolerance to biotic and abiotic stresses in many plant species. Most research about the uptake and beneficial effects of Si in plants has been carried out on monocotyledonous species, Si-accumulating plants. Little attention has been paid to woody crops, characterized as low-Si-accumulating plants. In this sense, available information about Si nutrition in olive trees is scarce. Therefore, this work aimed to study the effect of Si application on the uptake, accumulation, and organ distribution of Si in young olive plants by analyzing the influence of the dose, the method of application, and the cultivar. Three experiments were conducted under shade-house conditions with mist-rooted ‘Arbequina’ and ‘Picual’. The treatments consisted of different Si doses, ranging from 0 to 20 mg·L−1, depending on the experiment, applied by foliar sprays or through the irrigation water. Choline-stabilized orthosilicic acid (H4O4Si) was used as the source of Si. Results indicated that after 120 days of Si treatments, this element was accumulated in major proportion in the roots, followed by the leaves and the shoot of the plants. Si organ concentration increased according to the doses applied, independently of the olive cultivar and the method of Si application. Differences in leaf Si accumulation between treated and control plants were evident 60 days after its application. The dose of 20 mg·L−1 was the most effective to increase Si level in leaves under the trial conditions. Si is recommended to be applied periodically to ensure its accumulation in growing leaves.