Avocado (Persea americana Mill.) is a tropical fruit that has gained immense popularity worldwide due to its unique flavor, nutritional value, and numerous health benefits. The growth and maturation of avocados are influenced by various environmental and climatic factors. Temperature is one of the most critical factors, as it plays a significant role in various physiological processes of this fruit. This study aimed to investigate the effect of air temperature on avocado development and assess the harvest maturity period (determined by the dry matter content) of Fuerte, Zutano, and Hass, the most common avocado varieties, grown in Western Crete, Greece. Fruit samples collected from avocado orchards in five regions of Western Crete were subjected to dry matter analysis during the ripening period for the years 2017 to 2022. Maturation time is determined based on the EU regulation for dry matter concentration. The results of this study revealed that dry matter concentration can be affected by both very high summer temperatures and low temperatures during the ripening period. Specifically, high temperatures during the summer months can have a significant impact on avocado development and result in a reduced dry matter concentration. On the other hand, low temperatures during the maturation stage can slow down enzymatic activity and metabolic processes, resulting in delayed ripening and a prolonged time to reach optimal maturity. This delay in maturation and reduced dry matter concentration can significantly affect the harvest timing, as growers may need to wait for the avocados to develop the desired characteristics before they can be harvested. Our findings are the first data on avocado maturation (dry matter concentration) in relation to temperature and provide valuable insights into harvest maturity period of avocado cultivation in Crete and other regions with similar Mediterranean climatic conditions.

The market for avocado is one of the fastest expanding worldwide, inclduing the Mediterranean basin. Organic farming systems cannot make use of synthetic fertilizers and therefore rely on several cultural techniques to maintain vigorous young trees and for quick shoot development, satisfactory yield, and fruit quality. We studied the effect of three different organic products (Terra Insecta^® (Aeiphoria-Sustainable products of Crete, Chania, Greece), Fruit-Fix^®, and AMINO-16^® (both products manufactured by EVYP, Sindos, Thessaloniki, Greece) on avocado plants in the cool subtropical area of southern Greece. Three experiments were carried out, two of them on young avocado trees, and the third one on mature, fully productive trees. The establishment success (ES) (%), plants with shoot induction (SI) (%), plants with shoot growth ≥ 3 cm (SG) (%), number of sprouted buds ≥3 cm per plant (SB), mean shoot length (cm) per plant (SL), total shoot length (cm) per plant (TSL), mean leaf number per plant (LN), and total leaf number per plant (TLN) were measured in the first and second experiments, while in the third experiment, fruit growth parameters (length, width, fruit weight, fruit weight increase (FWI)) and fruit quality parameters (dry matter, oil concentration, dry matter, and oil concentration increase) were measured. The application of 0.2 K of Terra Insecta^® to the planting hole did not have any statistically significant effect on plant growth, but when added around the trunk, statistically higher values were observed for SB, SL, LN, TSL, and TLN in the Terra Insecta^® treatment compared to the control. Fruit-Fix^® application to Lamb Hass avocado trees resulted in significant differences in ES, SI, SG, SL, TSL, LN, and TLN, and in the Hass variety, in SB. In the AMINO-16^® experiment, the fruit dimensions, quality parameters, and yield of the Hass variety were not recorded as significantly different. However, in the Fuerte variety, FW increased by 119.3% in the AMINO-16^® treatment. The effect of the organic fertilizers used in this research showed noticeable results requiring studies to be carried out over more seasons, different tree ages, cultivation methods, and stress conditions.

In this study, the effect of increased soil moisture on the nutritional status of two key commercial avocado (Persea americana Μill.) cultivars, ‘Fuerte’ and ‘Hass’, was examined. The results revealed that prolonged exposure of plants to high soil water content conditions (waterlogging) reduced the total nutrient content (absolute quantity) of almost all of the nutrients in scion’s tissues (leaves and stems) of both cultivars. The decrease of nutrient content in the ‘Fuerte’ leaves was more prominent/severe compared to the ‘Hass’ leaves, which could be the outcome of the reported higher sensitivity of the cultivar to soil waterlogged conditions in previous studies. Interestingly, the inability of ‘Fuerte’ avocado plants to withstand high soil moisture conditions was not reflected in the relative concentrations of most nutrients, both in leaves and stems. Indeed, significantly higher concentrations of P, K, B, Fe, and Zn were found in the leaves of ‘Fuerte’ waterlogged plants than in well-watered ones. This fact reveals that under marginal/stressful conditions, like waterlogging, nutrient concentration in tissues does not reflect potential negative effects on total nutrient uptake of avocado plants, obviously due to concentrated nutrient phenomena primarily created by the stress-dependent growth inhibition. Therefore, total nutrient content is proposed as a more representative indicator for assessing plant response to waterlogged conditions.

Washingtonia filifera is important for its ecological, economic, cultural, horticultural, ornamental, and medicinal potential. Elicitation of in vitro cultures presents a promising and efficient method for the large-scale production of valuable bioactive compounds. This study assessed the effect of chitosan concentration (0, 20, 40, 60, 80, 100 mg L⁻¹) on biomass growth [fresh weight (FW), dry weight (DW)] and phytochemical profile [total phenolic content (TPC), total flavonoid content (TFC), DPPH antioxidant activity, total phenolic productivity (TPP), total flavonoid productivity (TFP)] in W. filifera callus and cell suspension cultures. Among different plant growth regulator combinations tested, 3 mg L⁻¹ 2,4-D + 0.5 mg L⁻¹ 2ip gave higher callus induction (90%) (MS medium, 12 weeks). A maximum growth curve (FW: 180 mg) of cell suspension culture was achieved 7 weeks after initiation (shaker at 90 rpm for 24 h). Cell suspension exhibited higher FW, DW, TPC, TFC, DPPH, TPP, and TFP than callus, while flavonoid production was higher than phenolic production. FW and DW were higher in both systems, with 40 mg L⁻¹ chitosan. Chitosan at 60 mg L⁻¹ best enhanced the phytochemical profile of both the 4-week solidified callus and the 7-week liquid cell suspension (TPC: 29.9 and 32.1 mg GAE g⁻¹ DW; TFC: 40.5 and 56.1 mg QE g⁻¹ DW; TPP: 969.2 and 1122.6 mg L⁻¹; TFP: 1313.9 and 1521.7 mg L⁻¹; DPPH: 87.4 and 92.3%), respectively, while 40 mg L⁻¹ chitosan was equally effective regarding DW, TFC, and TFP in cell suspension. Chitosan elicitation provides a powerful strategy to upregulate phenolic and flavonoid biosynthesis in W. filifera in vitro systems, conferring superior antioxidant potential. The identification of peak elicitation parameters (chitosan concentration, exposure time) allows for the targeted enhancement of bioactive compound yields, suggesting a viable path for industrial bioproduction and commercialization in pharmaceuticals, nutraceuticals, and functional foods, leveraging bioreactor technology for efficient scale-up.