Preharvest UV-C treatment affected postharvest senescence and phytochemicals alternation of strawberry fruit with the possible involvement of abscisic acid regulation.

As an environmentally friendly approach for fruit quality improvement, the effect of preharvest UV-C on the physiology of strawberry fruit during postharvest storage remains to be assessed. Strawberry fruit developed with supplementary UV-C were stored at room temperature for 2 weeks. Preharvest UV-C attenuated fruit postharvest senescence and altered phytochemicals composition. Higher ester titer was found in the treated fruit at harvest, whereas higher terpene and furanone contents were detected after 72 h of storage. At harvest, polyphenolics accumulated to a higher level in UV-C group, but the difference disappeared after 24 h of storage. Meanwhile, the intrinsic level of abscisic acid and the expressions of FaPYR1, SnRK2, and FaASR in the UV-C-treated fruit was enhanced at harvest but returned to a lower level as storage proceeded. This study highlights the time-dependent effect of preharvest UV-C on strawberry fruit postharvest biochemical indexes and the possible involvement of abscisic acid signaling factors.

Ultraviolet-C priming of strawberry leaves against subsequent Mycosphaerella fragariae infection involves the action of reactive oxygen species, plant hormones, and terpenes.

Ultraviolet-C (UV-C) radiation has been reported to induce defence responses to pathogens in growing crops and described as a new environmentally friendly method for disease control. However, whether the effect of the induced defence mechanisms will persist after the stress imposed by UV-C is alleviated and how these mechanisms interact with pathogen elicitors upon infection have not yet been investigated. Thus, we inoculated strawberry plants with Mycosphaerella fragariae, the causal agent of leaf spot disease, after 5 weeks of repeated UV-C irradiation treatment (cumulative dose of 10.2 kJ m-2 ) and investigated the alteration of gene expression and biochemical phenotypes. The results revealed that UV-C treatment had a significant impact on gene expression in strawberry leaves and led to the overexpression of a set of genes involved in plant-pathogen interaction. UV-C-treated leaves displayed a stronger response to infection after inoculation, with reduced symptoms and increases in accumulation of total phenolics and volatile terpenes, higher expression of pathogenesis-related proteins and the activity of several defence enzymes. This study presumptively describe, for the first time, the involvement of terpenes, reactive oxygen species, and abscisic acid, salicylic acid, jasmonic acid, and their transduction factors, in the network underpinning UV-C priming of growing crops for improved protection against pathogens.

Preharvest Ultraviolet C Treatment Affected Senescence of Stored Strawberry Fruit with a Potential Role of MicroRNAs in the Activation of the Antioxidant System.

Recent studies presented preharvest ultraviolet C (UV-C) as an environmentally friendly approach for the management of horticultural crop diseases. The effect of this approach on quality preservation during postharvest storage has not yet been investigated. Strawberry fruit harvested from plants grown with supplemental UV-C were stored at room temperature for 72 h, and their postharvest shelf-life biochemical indicators were evaluated. The involvement of microRNAs (miRNAs) in the activation of UV-C-induced antioxidant systems was investigated. Preharvest UV-C contributed to the preservation of sugar and organic acid and reduced overall lipid peroxidation in strawberry fruit during storage. We found that miR159 and miR398 were downregulated by preharvest UV-C and that their respective targets were upregulated at the early stage of storage with enhancement of the activity of antioxidant enzymes. The initial burst of H2O2 and O2• - suggested that preharvest UV-C primed the fruit in an antioxidative activated state via reactive-oxygen-species-mediated feedback control with post-transcriptional involvement of miRNAs.

Preharvest Ultraviolet C Irradiation Increased the Level of Polyphenol Accumulation and Flavonoid Pathway Gene Expression in Strawberry Fruit.

Preharvest ultraviolet C (UV-C) irradiation is an innovative approach for increasing the bioactive phytochemical content of strawberries to increase the disease resistance and nutritional value. This study investigated the changes in individual flavonoids in strawberry developed with three different cumulative doses of preharvest UV-C treatment (low, 9.6 kJ m-2; middle, 15 kJ m-2; and high , 29.4 kJ m-2). Significant accumulation (p < 0.05) of phenolics (25-75% increase), namely, cyanidin 3-glucoside, pelargonidin 3-glucoside/rutinoside, glucoside and glucuronide of quercetin and kaempferol, and ellagic acid, was found in the fruit subjected to low and middle supplemental doses of UV-C radiation. The expression of the flavonoid pathway structural genes, i.e., FaCHS1, FaCHI, FaFHT, FaDFR, FaFLS, and FaFGT, was upregulated in the low- and middle-dose groups, while the early stage genes were not affected by the high dose. FaMYB1 was also relatively enhanced in the low- and middle-dose groups, while FaASR was upregulated in only the low-dose group. Hormetic preharvest UV-C dose ranges for enhancing the polyphenol content of strawberries were established for the first time.

Pre-harvest UV-C irradiation triggers VOCs accumulation with alteration of antioxidant enzymes and phytohormones in strawberry leaves.

Recent studies have highlighted the biological and physiological effects of pre-harvest ultraviolet (UV)-C treatment on growing plants. However, little is known about the involvement of volatile organic compounds (VOCs) and their response to this treatment. In this study, strawberry plants were exposed to three different doses of UV-C radiation for seven weeks (a low dose: 9.6kJm-2; a medium dose: 15kJm-2; and a high-dose: 29.4kJm-2). Changes in VOC profiles were investigated and an attempt was made to identify factors that may be involved in the regulation of these alterations. Principle compounds analysis revealed that VOC profiles of UV-C treated samples were significantly altered with 26 VOCs being the major contributors to segregation. Among them, 18 fatty acid-derived VOCs accumulated in plants that received high and medium dose of UV-C treatments with higher lipoxygenase and alcohol dehydrogenase activities. In treated samples, the activity of the antioxidant enzymes catalase and peroxidase was inhibited, resulting in a reduced antioxidant capacity and higher lipid peroxidation. Simultaneously, jasmonic acid level was 74% higher in the high-dose group while abscisic acid content was more than 12% lower in both the medium and high-dose UV-C treated samples. These results indicated that pre-harvest UV-C treatment stimulated the biosynthesis of fatty acid-derived VOCs in strawberry leaf tissue by upregulating the activity of enzymes of the LOX biosynthetic pathway and downregulating antioxidant enzyme activities. It is further suggested that the mechanisms underlying fatty acid-derived VOCs biosynthesis in UV-C treated strawberry leaves are associated with UV-C-induced changes in phytohormone profiles.

Potential link between fruit yield, quality parameters and phytohormonal changes in preharvest UV-C treated strawberry.

Preharvest ultraviolet-C (UV-C) treatment of strawberry is a very new approach, and little information is available on the effect of this treatment on plant growth regulators. In this study, the effect of preharvest UV-C irradiations at three different doses on strawberry yield, fruit quality parameters and endogenous phytohormones was investigated simultaneously. The overall marketable yield of strawberry was not affected by the preharvest UV-C treatments, although more aborted and misshapen fruits were found in UV-C treated groups than in the untreated control. The fruits in the high dose group were firmer and had approximately 20% higher sucrose content and 15% higher ascorbic acid content than the control, while fruits from the middle and low dose groups showed no significant changes in these parameters. The lower abscisic acid (ABA) content found in the fruits in the high UV-C group may be associated with those quality changes. The citric acid content decreased only in the low dose group (reduction of 5.8%), with a concomitant 37% reduction in jasmonic acid (JA) content, compared to the control. The antioxidant status of fruits that received preharvest UV-C treatment was considered enhanced based on their oxygen radical absorbance capacity (ORAC) and malondialdehyde (MDA) content. In terms of aroma, three volatile alcohols differed significantly among the various treatments with obvious activation of alcohol acyltransferase (AAT) activity. The observed synchronous influence on physiological indexes and related phytohormones suggests that preharvest UV-C might affect fruit quality via the action of plant hormones.

Preharvest ultraviolet-C irradiation: Influence on physicochemical parameters associated with strawberry fruit quality.

Postharvest ultraviolet-C (UV-C) hormesis has been shown effective for the treatment of the edible part of several horticultural crops such as strawberry fruit; however, there is a lack of information on its potential preharvest impact. In the present study three strawberry cultivars (Fragaria × ananassa Duch. 'Albion', 'Charlotte' and 'Seascape') were exposed to UV-C during two growth seasons for a period of three weeks. Treatment begins when the first flowers were wide open and fruits at commercial maturity were harvested within one week after UV treatment. The physicochemical quality parameters of the fruits harvested from the treated plants were compared to those of the fruits of the untreated control plants. Preharvest UV-C treatment tended to increase fruit firmness in all cultivars with significant differences declared only for 'Albion' and 'Seascape' in season 2. Fruits from treated plants were generally redder but a significant difference was observed only for cultivar 'Charlotte' in the second growing season. Other color attributes were not affected by UV-C, neither were organic acids, simple sugars, soluble solids content (SSC), titratable acidity (TA) and pH, although in most cases slight decreases were noticed. Cultivar and growing season were the factors that mostly influenced on the parameters under study. The present study show that cumulative preharvest UV-C treatment of 3.6 kJ m-2 did not adversely affected important strawberry quality parameters.

Effects of preharvest ultraviolet-C irradiation on fruit phytochemical profiles and antioxidant capacity in three strawberry (Fragaria × ananassa Duch.) cultivars.

BACKGROUND: Ultraviolet-C (UV-C) has proven effective in extending shelf-life, reducing disease incidence and increasing the levels of health-promoting compounds in several crops. While most studies were conducted at the postharvest stage, our study examined the effect of preharvest UV-C application in three strawberry cultivars (Fragaria × ananassa Duch. 'Albion', 'Charlotte' and 'Seascape'). UV-C treatment was applied from the onset of flowering until the fruits reached commercial maturity on plants grown for two consecutive seasons under greenhouse conditions. The phytochemical profiles and antioxidant capacity of the fruits were assessed at harvest. RESULTS: The ellagic acid and kaempferol-3-glucuronide contents were significantly increased only in fruits of the cultivar 'Albion' collected from UV-C-treated plants in season 1. UV-C did not consistently affect the other phenolic compounds that were measured. Based on the results of the ferric-reducing antioxidant power, oxygen radical absorbance capacity and total phenolic content assays, the antioxidant capacity of the three strawberry cultivars was not affected by UV-C. Season and cultivar had a decisive impact on these parameters. CONCLUSION: The effect of preharvest UV-C on the levels of bioactive compounds in strawberry fruits appears to be cultivar- dependent, with season or growing conditions having a significant impact.