Experiments were carried out in 2018 and 2019 to evaluate the effects of a biostimulant of animal origin, with a hormone-like action, on the growth and physiology of young olive trees. The biostimulant, consisting of a complex of natural amino acids (glycine, proline, and hydroxyproline, etc.), was applied by fertigation to both potted (one-year-old) and field-grown (2 years after transplanting) young olive trees. The control consisted of trees treated with an amount of urea nitrogen equal to the total nitrogen supplied with the biostimulant. Potted trees treated with the biostimulant showed greater growth than the control soon after treatment and up to the end of the vegetative season. Generally, this was associated with higher leaf photosynthetic rates and stomatal conductance. At the end of the experiment, all tree parts (roots, stem, shoots, and leaves) of the treated trees had greater biomass than the control. The trunks of field-grown trees treated with the biostimulant had greater growth with respect to the control. Overall, the results indicate the possibility of using the biostimulant based on complexes of natural amino acids to promote the growth of young olive trees.

Seeds from Citrus species represent a relevant by-product of the juice industry and a potential source of bioactive compounds such as phenols and other antioxidants. Sprouting could be an intriguing idea to enhance the content of these compounds, as explored for other fruittree species. In this experiment, the sprouting performance, the concentration of total phenols and phenolic acids, and the antioxidant activity of seeds and sprouts were evaluated for bitter orange (Citrus aurantium L. seedlings), blonde orange (Citrus sinensis (L.) Osbeck cv.Biondocomune), sweet orange (Citrus sinensis (L.) Osbeck seedlings), lemon (Citrus limon (L.) Osbeck cv.Femminello), and mandarin (Citrus reticulata Blanco cv.Tardivo di Ciaculli). The germination was high for all genotypes except for mandarin, but it took 4–8 weeks. Sprouts did not differ among genotypes for size and generally had hard consistency of cotyledons and a bitter taste. The concentrations of total phenols and phenolic acids of seeds and sprouts varied with the genotype, while the antioxidant activity was not statistically different among treatments. Sprouting increased both the concentration of phenolic compounds and antioxidant activity but no correlation was found between them, suggesting that other antioxidants, besides phenols, are present. Given the slow germination and the bitter taste, Citrus sprouts appear unsuitable for homemade production aimed at direct consumption, while they may have perspectives for extraction of food additives, cosmetics, and pharmaceutics.

In 2019–2020, trials were carried out with the aim of evaluating the possibilities of using an organic fertilizer, reported to have a biostimulant action, for promoting the growth of young olive trees. The experiments were implemented using both potted and field-grown trees. The effects of the organic fertilizer were evaluated with respect to trees treated with a chemical fertilizer; for potted trees a control without any fertilization was also used. Therefore, the compared treatments were: organic fertilization vs. chemical fertilization or no fertilization in the experiment with potted trees; organic fertilization vs. chemical fertilization in the experiment with field-grown trees. Non-fertilized potted trees had the lowest growth. The organic fertilizer, with respect to the chemical one, determined higher growth in both potted and field-grown trees (+22–29% of the increment of the trunk cross sectional area). In potted trees, it determined a rapid elongation of the stem (+30% of the increment of tree height with respect to chemically fertilized trees) and this likely favored the development of a higher number of leaves, which, together with an increase in their photosynthetic activity (in August, +27% with respect to chemical fertilized trees), created conditions for higher assimilate production and in turn greater tree growth. Trees in the field showed that the greater growth was not obtained at the expenses of reproductive growth, which increased to the same degree as the vegetative growth. Overall, the results support the biostimulant action of the organic fertilizer and indicate the possibility of its use to improve the growth of young olive trees.

In 2019–2020, trials were carried out in both intensive (cultivar Moraiolo) and super-high-density (cultivar Sikitita) young olive orchards to drastically reduce early production and, consequently, accelerate tree growth. Different concentrations of naphthaleneacetic acid (NAA) (0 ppm–control, 20 ppm, 40 ppm, 80 ppm, 160 ppm and 250 ppm) were applied at full bloom (open flowers > 80%), using a shoulder sprayer, and their effects on vegetative growth and reproductive behavior were evaluated, also compared to manually deflowered trees. The treatments with NAA reduced fruit set (down to values close to zero) compared to the control, and the reduction was correlated with the NAA concentration. In particular, 160 ppm virtually eliminated fruit set and thus production in both Moraiolo and Sikitita cultivars. In Moraiolo, 160 ppm NAA and manual deflowering determined similar shoot and trunk growths, which were greater than in control trees. Application of 160 ppm NAA for two consecutive years gave a progressively higher increase in trunk growth compared to the control. In conclusion, in young olive trees, the treatment with 160 ppm NAA at full bloom practically eliminated fruit set and production, with a parallel great increase in vegetative growth. This can be exploited as a powerful technique to accelerate the growth of young olive trees in both intensive and super-high-density orchards, as well as in nurseries. A more rapid transition to the adult stage/size of the trees and to full production of the orchard allows us to anticipate the use of mechanical harvesting and the recovery of the planting investment.

In recent years, there has been growing interest in olive genotypes (Olea europaea L.) suitable for super-high-density (SHD > 1200 trees/hectare) orchards. To date, only a few cultivars are considered fitting for such cultivation system. In this study, the first results on the architectural characteristics of the canopy of ten new olive genotypes are presented. Their suitability for SHD orchards was evaluated and compared with the cultivar ‘Arbequina’, which is considered suitable for SHD olive orchards and, for this reason, was used as the control. Several canopy measurements were taken, and some architectural parameters, such as branching frequency, branching density, and branch diameter/stem diameter ratio were calculated. The branching frequency value was greater than 0.20 in ‘Arbequina’ and in only four of the genotypes. The branching density in five genotypes was similar to ‘Arbequina’. ‘Arbequina’ had the lowest value for the branch diameter/stem diameter ratio, and only three genotypes had similar values. These initial results showed that only one genotype has all canopy architectural characteristics comparable to those of the cv. ‘Arbequina’. Further studies are needed to evaluate the production traits of these new genotypes and complete their characterization.