María Emma García-Pastor

Blood orange maturation is a complex process and is not fully understood. We studied the on-tree ripening of ‘Sanguinelli’ cultivar picked in 10 stages (S1 to S10) in 4 different fruit sections: peduncle end, proximal and distal equator and stylar end. Results showed that as ripening advanced, chlorophyll decreased and anthocyanin increased, while carotenoid first enhanced (from S1 to S6) and then diminished in the rind, the concentration being dependent on the fruit section. We have found that chlorophylls were higher in the peduncle end and the proximal equator, anthocyanins were higher in the distal equator, while carotenoids were maximum at the peduncle end. Our results demonstrate that flesh anthocyanins, total soluble solids, total acidity increased parallelly to the ripening process, and again these quality attributes were affected by the assayed tissue. Overall, results suggest that the ripening process of ‘Sanguinelli’ blood orange exhibits a gradient pattern.

Adverse environmental and postharvest conditions challenge the functional quality of lemons, an economically vital citrus crop. Melatonin (MEL) has emerged as an effective regulator of plant stress responses and secondary metabolism. This study evaluated the effects of pre- and postharvest MEL treatments, combined with cold storage, on the fruit quality of two lemon cultivars (‘Fino’ and ‘Verna’). The research focused specifically on endogenous MEL and flavanone dynamics. Three experimental conditions were assessed: (a) preharvest MEL application at 0.1 and 1 mM; (b) preharvest treatment followed by cold storage; and (c) combined pre- and postharvest MEL treatment followed by cold storage. Preharvest treatments increased endogenous MEL at harvest in a dose- and cultivar-dependent manner. Specifically, 1 mM being optimal for ‘Fino’, while 0.1 mM was more effective for ‘Verna’. During cold storage, ‘Fino’ fruit, characterized by low basal endogenous MEL levels, showed a marked increase in MEL accumulation, suggesting the stimulation of biosynthesis. In contrast, ‘Verna’ fruit, which had initially high endogenous MEL content, exhibited a pronounced decline, indicating MEL consumption to counteract oxidative stress. Flavanone content increased dose-dependently after preharvest treatment and was preserved during storage in ‘Fino’ but declined in ‘Verna’. These findings demonstrate that the fruit cultivar must be considered a critical factor in MEL-based strategies, as identical treatments may yield markedly different outcomes even within the same species.

The ‘Mollar de Elche’ pomegranate cultivar is highly valued for its organoleptic properties, yet it often suffers from inadequate fruit pigmentation, reducing its commercial competitiveness. This study, carried out in a mature commercial orchard located in Spain (Alicante), evaluated the impact of preharvest applications of sorbitol at different concentrations (0, 0.1, 0.5, and 1% in 2023, and 2.5 and 5% in 2024) and three application periods: S1 (nine applications from fruit set), S2 (six applications from seed hardening), and S3 (three applications at the onset of colour change) over two consecutive growing seasons (2023 and 2024). Treatments were applied via foliar spraying from the time of fruit set until the onset of external colour change. The results showed that sorbitol acted as an effective metabolic ‘vector’, significantly increasing fruit weight and total yield, particularly at concentrations of 1 and 5%. Furthermore, sorbitol treatments enhanced fruit firmness by stabilizing cell wall structures and significantly improved exocarp red pigmentation by reducing the hue angle. While the highest doses (1, 2.5, and 5%) enhanced biomass accumulation, they also triggered a potential negative feedback loop in sugar sensing that could interfere with secondary metabolism at excessive thresholds. These findings suggest that preharvest sorbitol applications, particularly at concentrations between 1 and 5% starting from early application period (S1), serve as an effective strategy for improving yield and external pigmentation in ‘Mollar de Elche’ pomegranate fruit.

‘Mollar de Elche’ pomegranate is highly valued for its sweet flavor but faces significant commercial hurdles due to pale coloration and sensitivity to postharvest disorders. This study investigates the impact of preharvest foliar applications of L-α-amino acids, applied alone (AA) or combined with 2.5% sorbitol (Sor–AA), on secondary metabolism and physiological resilience, defined here as the fruit’s capacity to maintain metabolic homeostasis and stabilize antioxidant pigments during cold storage (7 °C). Our results show that both treatments triggered a substantial shift in secondary metabolism, doubling anthocyanin concentrations at harvest and effectively overcoming the cultivar’s color deficit. While the AA treatment maximized fruit quantity per tree, the Sor–AA combination achieved the highest total yield (83.58 ± 6.82 kg) and individual fruit weight (469.00 ± 16.00 g) through a ‘metabolic bypass’ that optimizes energy use. Crucially, the physiological resilience of the fruit was uniquely bolstered by the Sor–AA treatment, which was the only strategy to stabilize anthocyanin levels (~108 mg L⁻¹) and maximize free ellagic acid in the husk (371.72 mg kg⁻¹) throughout 42 days of storage. Multivariate PCA (explaining 79.79% of variance) confirmed that the synergy of amino acids and sorbitol triggers systemic metabolic reprogramming. Consequently, this targeted agronomic approach could provide significant economic benefits by increasing the proportion of export-grade fruit and extending the commercial window for the pomegranate sector.

Yellow pitahaya (Selenicereus megalanthus Haw.) is increasing in popularity and is considered to be an exotic fruit with great potential for consumption due to its content of both nutritive and bioactive compounds with health-related properties. Pitahaya plants, grown in Ecuador, were treated with two elicitors: methyl jasmonate (MeJA) and methyl salicylate (MeSA), both at a 0.1 mM concentration. After harvesting, the fruits were transported to Spain and stored at two temperatures, 2 and 10 °C, for 55 days. The analytical determinations were physiological parameters (ethylene and respiration rates), organoleptic traits [firmness, color, total soluble solids (TSSs) and total acidity (TA)], and phytonutrients (total phenolics, carotenoids and total antioxidant activity). The results show that all the parameters evolved more rapidly at 10 °C than at 2 °C, which is due to storage temperature effects on fruit metabolism. For TSSs, reductions were observed at the two temperatures, while, for TA, a major reduction was obtained at 2 °C. Regarding storage, the respiration rates increased, especially at 2 °C. At the end of storage, total phenolics were higher in treated pitahayas. Moreover, fruits developed chilling injury (CI) at 2 °C based on the highest respiration rate and accelerated softening. Collectively, all the data suggest that both MeJA and MeSA could modulate yellow pitahaya ripening without detrimental effects on quality during postharvest storage.

Jasmonic acid (JA) and its derivative, methyl jasmonate (MeJa), are naturally occurring plant hormones involved in alleviating abiotic stresses, such as exposure to extreme temperatures (cold or heat), flooding and drought. JA content increased following MeJa applications at pre- or postharvest, regulating several physiological and biochemical processes during fruit growth and ripening. As a preharvest treatment, MeJa increased crop yield and improved the organoleptic quality of the fruit. Regarding postharvest applications, MeJa reduced the chilling injury symptoms in sensitive fruits when they were stored at cold temperatures. In addition, there is some evidence of crosstalk between JA and other plant hormones. In this review, we highlight the mechanisms by which jasmonates contribute to plant stress resistance, regulating the biosynthesis and metabolism of abiotic stress and improving fruit quality.

Sweet cherry (Prunus avium L.) is a highly appreciated fruit species for consumption but susceptible to climate change-induced weather, such as heavy rainfall, which catastrophically compromises yield and commercial fruit quality. Brassinosteroids (BRs) represent a novel biologically safe class of hormones that have been shown to increase plant resilience against these adversities and enhance crop yield and fruit quality in some fruit species. The main aim of this study was to evaluate the potential efficacy of the preharvest foliar spray treatments with 24-epibrassinolide (24-BL) at 0.01, 0.1 and 1 µM on crop yield, cracking incidence and fruit quality of ‘Sunburst’ and ‘Skeena’ sweet cherry cultivars, during two seasons with different weather conditions (2022 and 2023). Results revealed that 24-BL treatments improved fruit growth, fruit weight, and increased commercial crop yield, especially at 0.1 µM during the first season. Notably, in 2023, when extreme rainfall occurred, 24-BL at 0.01 and 0.1 µM significantly decreased cracking incidence by up to 50% for ‘Skeena’. Additionally, firmness, red colour and bioactive compounds, such as total phenolics and total anthocyanins, were also found at higher levels in fruits from 24-BL-treated trees compared to controls, in both cultivars and years. In conclusion, the foliar spray application of 24-BL at 0.01 µM and, especially at 0.1 µM, can be a useful and eco-friendly tool to reduce cracking incidence, improve crop yield and enhance sweet cherry quality traits regardless of environmental negative events, such as heavy rainfall. Importantly, the enhancement of bioactive compounds would promote additional antioxidant properties and enhance health benefits to consumers.

Melatonin (MEL), also known as N-acetyl-5-methoxytryptamine, has been reported in plants as a secondary messenger involved in regulating abiotic stress responses. MEL treatment, either preharvest or postharvest, regulates several physiological and biochemical processes during fruit growth and ripening in horticultural products. These include reproductive development, tissue and quality maintenance, delayed senescence, and responses to abiotic stress. Due to its natural origin, low toxicity, and multifunctional regulatory capacity, MEL has recently attracted attention as a promising ‘green preservative’ for sustainable postharvest management. Additionally, MEL coordinates through cross-talk with other plant hormones, such as abscisic acid, ethylene, polyamines, jasmonic acid, γ-aminobutyric acid, salicylic acid, and nitric oxide, to regulate postharvest ripening and senescence. Furthermore, MEL enhances antioxidant systems and improves membrane integrity, thereby alleviating chilling injury and enhancing fruit firmness and colour. Notably, recent evidence highlights the innovative regulatory mechanisms of MEL involving redox homeostasis, hormone signalling reprogramming, and transcriptional modulation of stress-responsive pathways. MEL could therefore be considered an emerging, eco-friendly tool for prolonging the shelf-life of fruit and vegetables and maintaining their quality. This review summarises the mechanisms by which MEL contributes to plant stress resistance by regulating the biosynthesis and metabolism of stress tolerance and improving fruit quality.