Internal Ethylene Research Articles

The Expression of Key Ethylene and Anthocyanin Biosynthetic Genes of 'Honeycrisp' Apples Subjected to the Combined Use of Reflective Groundcovers and Aminoethoxyvinylglycine in the Mid-Atlantic US.

The decreased profitability of important apple cultivars, such as 'Honeycrisp', results from the poor red skin coloration and high fruit drop in the mid-Atlantic US. Apple red skin coloration is determined by the anthocyanin concentration. Reflective groundcovers promote red skin coloration, whereas aminoethoxyvinylglycine (AVG) decreases the ethylene production and fruit drop, thus reducing the coloration. Although our previous study showed that combinations of these practices impact the fruit quality and color, research is lacking regarding their effects at the gene and metabolite levels. In this work, for two years, we compared the differences in the internal ethylene concentration (IEC), red skin coloration, fruit drop, transcript accumulation of key ethylene and anthocyanin biosynthetic pathway-related genes, and total anthocyanin concentration of 'Honeycrisp' apples. The fruit was treated with combinations of reflective groundcover (Extenday) and AVG (130 mg L-1) and was assessed throughout ripening. Extenday-only-treated fruit displayed the highest upregulation of ethylene and anthocyanin biosynthetic-related genes and of total anthocyanins, exceeding 50% blush, while boosting the IEC. In contrast, AVG significantly decreased the expression of key ethylene and anthocyanin biosynthetic-related genes and total anthocyanins, thus preventing apples from reaching 50% blush, while also decreasing the IEC and fruit drop. The combination of Extenday x AVG fine-tuned the transcript accumulation of ethylene and anthocyanin biosynthetic-related genes as well as the total anthocyanins, allowing the 'Honeycrisp' fruit to exceed 50% blush, while increasing the IEC moderately and reducing the fruit drop (as compared to Extenday-only and control), thus enhancing the fruit economic value.

Combining the Use of Reflective Groundcovers and Aminoethoxyvinylglycine to Assess Effects on Skin Color, Preharvest Drop, and Quality of ‘Honeycrisp’ Apples in the Mid-Atlantic US

Apples are one of the most valuable fruits worldwide. ‘Honeycrisp’ is the top sales-producing cultivar in the US. Lack of red skin coloration and increased preharvest fruit drop significantly reduce the market value for cultivars such as ‘Honeycrisp’. The use of reflective groundcovers has been shown to enhance apple skin coloration. While the use of plant growth regulator AVG reduces fruit drop, it negatively affects skin coloration. Studies on the impacts of these practices in mid-Atlantic US-grown apples are limited. In this work, for two years, we compared differences in the light environment, fruit drop, internal ethylene concentration (IEC), physicochemical parameters, and skin coloration of ‘Honeycrisp’ apples in the lower third of the canopy. Apples were submitted to four treatment combinations of reflective groundcover (Extenday) and AVG (130 mg L−1). Assessments occurred throughout three ripening stages. Our results demonstrated that Extenday significantly promoted skin coloration (>75% blush) via the increased reflectance of photosynthetic photon flux density and UV radiation, and increased IEC, while also advancing fruit maturity, i.e., overripening. Conversely, AVG significantly minimized fruit drop and decreased EIC, delaying fruit maturity but drastically reducing red coloration (30–48% blush). The combined use of Extenday and AVG had a synergistic effect by decreasing fruit drop while enhancing fruit with >50% blush, without promoting overripening. Combining Extenday and AVG can boost the market value for ‘Honeycrisp’ apples in the mid-Atlantic US.

Reflective groundcovers promote anthocyanin content and advance fruit maturity of 'Evercrisp' apples grown in the Mid-Atlantic US.

Enhanced skin blush is critical in many apple cultivars to ensure crop profitability and acceptability. Anthocyanin content is a crucial determinant of apple skin blush. Reflective groundcovers are a preharvest management strategy that can improve apple skin blush, but integrative studies assessing its effects at the environmental, physiological, gene, and metabolite levels are lacking. In the present study, we assessed the impact of reflective groundcovers on light environment, preharvest fruit drop, internal ethylene concentration (IEC), fruit-quality-related physicochemical parameters, skin coloration, expression levels of important anthocyanin biosynthesis-related structural genes and transcription factors, and total anthocyanin content of 'Evercrisp' fruit located in the canopy's lower third during on-the-tree ripening, for 2 years, under mid-Atlantic US conditions. Fruit treated with reflective groundcovers displayed an enhanced red skin coloration, reaching >60% blush 1 week before commercial harvest and 2 weeks earlier than control fruit. This resulted from a significantly increased transcript accumulation of anthocyanin biosynthesis-assessed genes, which was promoted by an increased light reflectance (>5-25 times greater than control), which also led to a correspondingly higher total anthocyanin content. Additionally, reflective groundcover-treated 'Evercrisp' fruit also exhibited an increased IEC and an advanced maturity, but without differences in fruit drop, as compared to control fruit, during on-the-tree ripening. Reflective groundcovers deployment would allow for an earlier harvest (of at least one week) of 'Evercrisp' fruit, which would be packing out in the premium grades as compared to control, thus increasing fruit crop value.

Aminoethoxyvinylglycine Reduces Preharvest Fruit Drop and Fruit Ethylene Evolution in ‘Red Delicious’ Apple but Affects Fruit Size and Quality Inconsistently

Aminoethoxyvinylglycine (AVG) is widely used in commercial apple (Malus ×domestica Borkh.) production to reduce preharvest fruit drop (PFD) and delay ripening for harvest management. Recently, the maximum allowable concentration of AVG was doubled (up to 264 mg⋅L−1). Reports of the relationship between the AVG concentration and fruit growth, size, and quality have been contradictory. We evaluated the relationship between the AVG concentration and PFD, fruit size, fruit quality, and expression of ethylene signaling-related and cell wall modification-related genes. Experiments were conducted in 2019 and 2020 using mature ‘Red Delicious’ in western North Carolina. The AVG treatments [0 and 132 (AVG-1x) and 264 mg⋅L−1 (AVG-2x)] were applied 3 weeks before the expected harvest. The AVG treatments reduced fruit drop and internal ethylene concentration relative to the control in both years. There was no difference in drop between AVG-1x and AVG-2x applications. Only in 2020 did AVG treatments delay fruit softening and starch hydrolysis and reduce soluble solids concentration. There were no effects on red fruit color development. Fruit size was unaffected by AVG in 2019, but it was reduced in 2020 with the AVG-2x application. AVG reduced ethylene synthesis and altered signaling, evidenced by decreased relative expression of genes related to ethylene signaling (ARGOS1, ARGOS2). AVG applications also reduced the expression of EXPA8;1, suggesting that reduced cell wall disassembly was associated with a reduction in fruit softening. These results indicate that preharvest applications of 132 mg⋅L−1 AVG effectively reduced PFD via altering ethylene evolution and signaling. Use of a higher AVG concentration was of limited benefit.

Variability of index of absorbance difference (IAD) to indicate fruit maturity at harvest for major apple cultivars in Ontario

The overall objective of this study was to evaluate the index of absorbance difference ( IAD) of four major apple cultivars in Ontario (‘Honeycrisp’, ‘Ambrosia’, ‘Gala’, and ‘McIntosh’) during the harvest window over multiple seasons (≥4 years), as well as its relationship with fruit firmness, internal ethylene concentration, and starch index values. IAD values differed among the four cultivars, with ‘McIntosh’ having the highest IAD (1.03–1.33) overall and ‘Gala’ having the lowest (0.19–0.56). Principal component analysis showed that the cultivars were separated into distinct groups. ‘Honeycrisp’ was clustered with starch and ethylene, while ‘Gala’ and ‘McIntosh’ were mainly clustered with firmness and IAD, respectively. Variable correlations between IAD and other maturity indices were found over the years. The negative relationship between IAD and ethylene for ‘Gala’ showed variability with R2 ranging from 0.008 in 2012 to 0.47 in 2018. The correlation between IAD and starch for ‘Gala’ was very strong ( rs = −0.82****) in 2018, whereas it was not significant in any year for ‘McIntosh’. Overall, IAD may relate to harvest maturity, but it did not correlate closely or consistently with other maturity indices, varied greatly year to year, and was cultivar dependent. IAD measures are not consistently related to fruit maturity every year, making reliability difficult to attain.

Superficial scald development in ‘Granny Smith’ and ‘Nicoter’ apples: The role of key volatile compounds when fruit are stored under dynamic controlled atmosphere

A positive correlation of α-farnesene and its oxidation metabolites with superficial scald is commonly reported in apples stored in air or controlled atmosphere (CA) systems, where O2 levels are above the lower oxygen limit (LOL) tolerated by the fruit. Nevertheless, the LOL can be monitored by the dynamic controlled atmosphere (DCA) techniques and to provide different physiological responses. Therefore, this study aimed to evaluate key volatile metabolites from ‘Granny Smith’ and ‘Nicoter’ (‘Kanzi®’) apples stored under dynamic controlled atmosphere (DCA) monitored by respiratory quotient (RQ), i. e. at extremely low oxygen partial pressures (ELO) and correlate their emissions with the incidence of superficial scald (SS). The volatile compounds (VCs) were isolated by solid phase microextraction (HS-SPME) and analyzed by gas chromatography. For the first time, higher concentrations of α-farnesene and its oxidation metabolites (6-methyl-5-hepten-2-one, and 6-methyl-5-hepten-2-ol) were negatively correlated with SS in DCA-RQ. This is likely due to the higher levels of ethanol in fruit stored under this condition having an inhibitory effect on SS incidence even when α-farnesene, 6-methyl-5-hepten-2-one, and 6-methyl-5-hepten-2-ol accumulate. Additionally, SS is more correlated to internal ethylene concentration (IEC) than α-farnesene accumulation and their metabolites, even when fruit were stored under ELO, where ethylene action is reduced.

Short-term storage of ‘Honeycrisp’ apples at 0.5 oC does not improve control of bitter pit without increasing low temperature-induced physiological disorders

‘Honeycrisp’ apples are conditioned at 10 °C for 7 d before storage at 3 °C to reduce development of low temperature disorders such as soft scald. Conditioning, however, can result in greater risk of bitter pit development. A strategy to compromise between two types of disorder by storing fruit for short periods at 0.5 °C before being transferred to 3 °C showed promise in earlier research. Here, this strategy has been investigated over three years. Fruit were conditioned or not conditioned for 1 week at 10 °C before being stored at 0.5 or 3 °C. Fruit stored at 0.5 °C were moved to 3 °C after 1, 2, 3, 4, or 6 weeks in year 1; 5 weeks in year 2; and 1, 2, 3, 4, 6, or 8 weeks in year 3. Fruit quality and incidence of physiological disorders assessed after 16 weeks in years 1 and 2, and 20 weeks in year 3, plus 4 d at 20 °C. Internal ethylene concentration (IEC) and concentrations of acetaldehyde, ethanol and ethyl acetate of the fruit were measured during storage in year 3. Storage at 0.5 °C for different durations before transferring fruit to 3 °C in different years did not inhibit bitter pit or soft scald development compared with 0.5 or 3 °C with or without conditioning for 1 week at 10 °C. Fruit quality was not affected by storage temperature manipulation in any year. Bitter pit incidence correlated negatively with that of soft scald, and positively with IEC. Acetaldehyde, ethanol and ethyl acetate concentrations reached a maximum at 6–8 weeks of storage, but were not consistently related to treatment differences on soft scald incidence. However, volatile accumulations were associated with increasing severity ratings when fruit were categorized by disorder severity. Cavities and vascular browning of fruit were increased by short-term periods at 0.5 °C in year 3. Previous research suggesting that temperature manipulations could be used to manage soft scald and bitter pit incidence was not supported by this study.

Organic Aminoethoxyvinylglycine Is an Effective Alternative for Reducing Apple Preharvest Drop

Organic apple (Malus ×domestica Borkh.) growers lack effective strategies to manage preharvest drop. For susceptible cultivars, yield losses caused by preharvest drop can exceed 30% at the beginning of harvest. To address this issue, a formulation of aminoethoxyvinylglyine (AVG) designed for organic use was developed and compared with a commercially available AVG formulation. We evaluated the effects and interactions of the AVG formulation and application number on preharvest drop and fruit maturity in 2017 and 2018. We selected 30 pairs of mature ‘Oregon Spur II Red Delicious’/‘M. 111’ trees planted at the Mountain Horticultural Crops Research and Extension Center in Mills River, NC, USA. Trees were planted with spacing of 2.7 × 6.1 m, trained to a central leader, and received plant protectant sprays that adhered to local recommendations throughout the growing season. Both AVG formulations were applied at 132 mg⋅L−1 at 3 or 3 + 1 weeks before the anticipated harvest. An untreated control was also included for comparison. The experiment had six replicates and a randomized complete block design with a 2 × 2 augmented factorial treatment structure. A one-way analysis of variance was performed and single degree of freedom contrasts were used to compare treatment groups of interest. During both years, organic and conventional AVG were equally effective for reducing preharvest drop and delaying fruit softening and starch hydrolysis at harvest. During one year, increasing the number of applications of AVG reduced cumulative fruit drop, delayed fruit softening at harvest, and reduced internal ethylene concentrations. Inconsistencies in responses across years may be explained, in part, by abnormally warm temperatures observed in 2018. AVG approved for organic use appears to be a promising preharvest drop management technology with efficacy similar to that of conventional AVG.

Xylem Functionality Is Not a Direct Indicator of Apple Preharvest Fruit Drop

Apple (Malus ×domestica) growers can incur significant economic losses when fruit drop before they can be harvested [preharvest fruit drop (PFD)]. In some years and cultivars, more than 30% of potential yield can be lost. Growers frequently apply plant bioregulators to reduce PFD, either via delay in maturity [aminoethoxyvinylglycine (AVG), 1-methylcycolpropene] or via inhibition in production of cell hydrolysis enzymes in the fruit pedicel [naphthalene acetic acid (NAA)]. Finding a physiological indicator of PFD would allow growers to assess the susceptibility of fruit to PFD. Due to its lignification, xylem is believed to be the last tissue to break down in the fruit pedicel, leading to PFD. To determine whether loss in xylem functionality can be used as an indicator of PFD potential, studies were conducted in 2020 and 2021 with ‘Red Delicious’ treated with AVG (132 µL·L−1), NAA (10 µL·L−1), and an ethylene-producing compound [ethephon (150 µL·L−1 in 2020, 200 µL·L−1 in 2021)] to generate a range of PFD potentials. Xylem functionality was assessed in the fruit cortex. Internal ethylene content (IEC), fruit maturity indices, and PFD rates were quantified weekly throughout the harvest period. Expression of genes encoding for cell hydrolysis enzymes (MdEG1 and MdPG2) was quantified to relate xylem functionality to fruit abscission mechanisms. In 2020 and 2021, AVG reduced PFD compared with the untreated control by decreasing IEC. Although ethephon did not result in higher PFD than untreated fruit, NAA reduced PFD in 2020 but not 2021. For all treatments in both years, there was a linear decrease in xylem functionality throughout the measurement period. Cumulative PFD exponentially decreased as xylem functionality neared zero and the climacteric rise in ethylene began. Concurrent with the rise in IEC and PFD was an increase in the expression of MdEG1 and MdPG2 in the fruit pedicel of the control compared with AVG-treated fruit. AVG-treated fruit lost xylem functionality at a similar rate to the untreated control but had lower expression of MdEG1 and MdPG2. These results indicate that xylem functionality is not a sole direct indicator of PFD. The concurrent increase in PFD and expression of MdEG1/MdPG2 supports previous research indicating that these two genes may serve as potential markers for PFD.

Harvest Maturity and Preharvest Aminoethoxyvinylglycine Treatment Effects on Cold-induced Ethylene Production of ‘Gala’ Apples

Cold storage is a commonly adopted technology to maintain quality and extend shelf life; however, depending on the cultivar, ethylene production can be enhanced by short-term cold treatments. In this study, index of absorbance difference (IAD) values, which reflect skin chlorophyll concentrations of cold-influenced ripening patterns, of ‘Gala’ apples were investigated. Fruit that were untreated or treated with aminoethoxyvinylglycine (AVG), which is a plant growth regulator that inhibits ethylene production of fruit, were harvested from a commercial orchard. Two IAD value categories 0.6 to 0.8 and 0.2 to 0.4 were chosen from a single harvest in 2019, whereas in 2020, the fruit in categories 0.6 to 0.8 and 0.2 to 0.4 were chosen for two harvests separated by 1 week, respectively. In 2019, only ethylene production was measured. In 2020, ethylene production, respiration, internal ethylene concentration (IEC), flesh firmness, 1-aminocyclopropane-1-carboxylate (ACC), and malonyl 1-aminocyclopropane-1-carboxylate (MACC) concentrations of fruit kept in air at 20 °C or stored at 0.5 °C for 21 days and then transferred to 20 °C were measured. The results were different from those described in the literature for cold-enhanced ethylene production of ‘Gala’ apples. Although ethylene production occurred without cold exposure of untreated fruit, exposure of fruit to 0.5 °C for 21 days resulted in more rapid and higher ethylene production rates and IEC than for fruit kept at only 20 °C. Ethylene production was suppressed by the preharvest AVG treatment, especially in 2020. The rates of respiration and softening of non-AVG treated fruit were enhanced by cold treatment. The effects of cold treatment were more significant for less mature fruit as indicated by higher IAD values.

Proteomic changes in association with storage quality of ‘Honeycrisp’ apples after pre and postharvest treatment of 1-MCP

1-Methylcyclopropene (1-MCP) is a well-known ethylene action inhibitor that has been applied to fruit after harvest to maintain fruit quality and extend storage life. Recently, the preharvest application of 1-MCP in a sprayable form has been developed and has demonstrated some beneficial effects to prolong harvest window and improve fruit quality. To gain understanding of molecular mechanisms for 1-MCP treatment, as both pre- and postharvest applications on apples, we conducted a quantitative proteomic experiment employing stable isotope labeling by peptide dimethylation on ‘Honeycrisp’ apples to reveal the significantly changed protein abundance in relationship to fruit quality after preharvest 1-MCP (Harvista™), postharvest 1-MCP treatments as well as their combination. We revealed the treatment affected fruit internal ethylene concentration, fruit quality indices and storage disorders incidence after 7 months of storage at 3 °C. Our quantitative proteomic study identified and quantified more than 600 proteins. Among the identified proteins, 312 proteins were found in common from all treatments, while 141 proteins abundance were changed with regards to preharvest, postharvest and the combination treatments of 1-MCP. We identified a few proteins that were only shown as result of preharvest 1-MCP treatment, while postharvest 1-MCP and in combination with preharvest treatment led to larger number proteins with reduced abundance. These results revealed and confirmed that postharvest 1-MCP and in combination with preharvest 1-MCP treatment affected ethylene biosynthesis, stress resistance, amino acid biosynthesis, antioxidant and redox system metabolisms. Potential metabolic changes resulting from 1-MCP treatment were found, and the efficacy of preharvest 1-MCP treatment was also discussed.

Evaluating the Classification of Freeze-Dried Slices and Cubes of Red-Fleshed Apple Genotypes Using Image Textures, Color Parameters, and Machine Learning

Dried red-fleshed apples are considered a promising high-quality product from the functional foods category. The objective of this study was to compare the flesh features of freeze-dried red-fleshed apples belonging to the ‘Alex Red’, ‘Trinity’, ‘314’, and ‘602’ genotypes and indicate which parameters and shapes of dried samples are the most useful to distinguish apple genotypes. Apple samples were at the stage of harvest maturity. The average fruit weight, starch index, internal ethylene concentration, flesh firmness, total soluble sugar content, and titratable acidity were determined. One hundred apple slices with a thickness of 4 mm and one hundred cubes with dimensions of 1.5 cm × 1.5 cm × 1.5 cm of each genotype were subjected to freeze-drying. For each apple sample (slice or cube), 2172 image texture parameters were extracted from images in 12 color channels, and color parameters L*, a*, and b* were determined. The classification models were developed based on a set of selected image textures and a set of combined selected image textures and color parameters of freeze-dried apple slices and cubes using various traditional machine-learning algorithms. Models built based on selected textures of slice images in 11 selected color channels correctly classified freeze-dried red-fleshed apple genotypes with an overall accuracy reaching 90.25% and mean absolute error of 0.0545; by adding selected color parameters (L*, b*) to models, an increase in the overall accuracy to 91.25% and a decrease in the mean absolute error to 0.0486 were observed. The classification of apple cube images using models including selected texture parameters from images in 11 selected color channels was characterized by an overall accuracy of up to 74.74%; adding color parameters (L*, a*, b*) to models resulted in an increase in the overall accuracy to 80.50%. The greatest mixing of cases was observed between ‘Alex Red’ and ‘Trinity’ as well as ‘314’ and ‘602’ apple slices and cubes. The developed models can be used in practice to distinguish freeze-dried red-fleshed apples in a non-destructive and objective manner. It can avoid mixing samples belonging to different genotypes with different chemical properties. Further studies can focus on using deep learning in addition to traditional machine learning to build models to distinguish dried red-fleshed apple samples. Moreover, other drying techniques can be applied, and image texture parameters and color features can be used to predict the changes in flesh structure and estimate the chemical properties of dried samples.

Tween-80 on Water/Oil Interface: Structure and Interfacial Tension by Molecular Dynamics Simulations.

Surfactants are used in many fields of the chemical industry in a wide range of applications. Generally, surfactants on water/oil interfaces reduce interfacial tension, enabling the formation of emulsions or providing greater stability to the emulsion formed. Although molecular dynamics has been extensively used and has achieved remarkable success in describing thermodynamic and molecular properties of systems with surface-active compounds, the traditional molecular simulation force fields considerably constrain the system size and the time scale of simulations. Here, we propose a coarse-grained model of polysorbate 80, a nonionic surfactant commercially known as Tween-80. Based on the proposed coarse-grained model, we evaluate the influence of the more internal ethylene oxide chain on the properties of the water/Tween-80/decane system. We verify with the simulation results that the model can reproduce the expected decrease in interfacial tension as the surfactant quantity increases in the simulations. Furthermore, we observe changes in the surfactant orientation as their quantity in the interface increases, indicating a preferential orientation for these molecules in the adsorption layer. We also assessed the partition coefficient of the surfactant between the two bulk phases by performing free energy calculations, which showed a higher affinity of Tween-80 surfactants with the water phase.

Non-destructive determination of ripening in melon fruit using time-resolved spectroscopy

The aim of this work was to explore the feasibility of time-resolved reflectance spectroscopy (TRS) in determining the ripening degree and the quality of orange-fleshed melons. Sixty ‘Honey Moon’ melons were measured by TRS in the 540-1064 nm range and classified as less (LeM), medium (MeM), and more (MoM) mature according to increasing values of μa540. MoM fruit showed yellower peel color, slightly more orange pulp, higher juiciness and higher carotenoid contents than LeM ones. MoM fruit also showed higher internal ethylene concentration and lower firmness than LeM ones, even if the differences were not significant. The μa540 was positively related to internal ethylene, carotenoid accumulation, and juiciness, indicating that μa540 was linked to different ripening processes in melons. However, the relationship between μa540 and total carotenoid content was not as high as expected due to the low variability of pulp color and of carotenoid content. Changes in flesh color toward a more orange shade were accompanied by increased juiciness and ethylene production and by carotenoid accumulation, while changes in peel color were associated with changes in flesh firmness and juiciness. In conclusion, the absorption coefficient measured at 540 nm (μa540) by TRS could be used to sort melons in different ripening degrees; however, its applicability will need to be evaluated on a larger number of fruits and on other varieties.

Assessing apple coming from agroclimatic differing locations: a tool for evaluating impact of environmental variation on postharvest

ABSTRACT The potential effect of preharvest environmental variation on the postharvest behaviour of apples (Malus domestica Borkh.) was assessed for ‘Cripps Pink’ variety apples grown in four different agroclimatic locations along the irrigated valley of Central Chile (Llancanao, Malloa, El Radal and El Parrón). The flesh firmness, total soluble solids (TSS), skin colour, internal ethylene concentration (IEC), internal browning (IB) and index of absorbance difference (IAD) were assessed in apples that had been stored at 0.5 and 2°C for 4 and 6 months and correlated with environmental parameters prior to harvest (February). There was notable variation in the IAD, percentage of red-coloured skin, TSS, firmness and IEC among the orchards at both storage temperatures, and both radial and diffuse IB were identified. Further analysis showed that the preharvest environmental conditions were correlated with the evaluated parameters, with five significant correlations (P < 0.05) being found and 63 of the 120 correlations examined having r values above 0.5. These findings indicate that preharvest environmental conditions affected fruit parameters during storage, which has implications under climate change.

Integrated multi-omic analysis of fruit maturity identifies biomarkers with drastic abundance shifts spanning the harvest period in ‘Royal Gala’ apple

Accurate assessment of apple fruit maturity at harvest is required since fruit harvested too early or too late are susceptible to physiological disorders or excessive softening during subsequent storage. Biological markers of early fruit maturity allow forecasting of optimal harvest time, contributing significant industry value through more accurate management of harvest logistics. This study investigated the changes in cortex of apple (Malus x domestica ‘Royal Gala’) fruit at four harvests: very early (H1), early (H2), commercial (H3) and late (H4), using a combination of transcriptomics, metabolomics, hormone abundances and enzyme activity profiles. Harvest times were discriminated based on several sets of variates, showing that metabolism was very active within this short time period. Good discrimination between H1 and H2 and between H2 and H3 was observed in the declining abundance of a range of photosystem transcripts and the increasing abundance of early ripening markers. Degradation of the photosynthetic apparatus was correlated with ethylene production. Multi-omics analysis using mixOmics identified groups of variates whose abundance declined or increased during the harvest period, and strong correlations between components of different pathways were evident. We identify a suite of biomarkers, including Chl a/b binding protein of LHCII, Xyloglucan glycosyltransferase 5, PG1, ACO1, internal ethylene concentration and starch pattern index, for orchardists to accurately predict harvest time several weeks in advance, thus providing time to mobilise the necessary logistical resources.

Fermentative metabolism of three apple cultivars during storage under low partial pressures of oxygen

The effects of low partial pressures of oxygen (pO2) on metabolism and fermentation-related gene expression of 'Empire', 'Jonagold' and, 'Fuji' apples have been investigated. Fruit were stored in 0.5, 1.0, and 1.5 kPa O2 (with 1 kPa CO2) at 0.5 °C for up to 6 months. During storage the lowest internal ethylene concentrations were observed in the 0.5 kPa O2 for ‘Empire’ and ‘Fuji’, but the pO2 did not affect those of ‘Jonagold’. pO2 did not affect flesh firmness of ‘Empire’ and ‘Fuji’ because little softening occurred in pO2, but for ‘Jonagold’ firmness was inversely related to pO2. In general, fermentation increased during storage in 0.5 kPa O2 but not in 1.5 kPa O2. However, 0.5 kPa O2 led to up-regulation of MdPDC2 and MdADH1 and down-regulation of MdADH3 in ‘Empire’ and ‘Fuji’, while expression levels of these genes at all pO2 in ‘Jonagold’ were similar. Metabolic responses to pO2 were affected by genetic background. We observed that regulation of MdADH1 is a key factor in control of ethanol accumulation of 'Empire' and 'Fuji' apples. On the other hand, MdADH1 in 'Jonagold' may be associated with stress tolerance to low O2 rather than with fermentation product biosynthesis.

Effects of 1-methylcyclopropene treatment on fruit quality and antioxidant activities of ruby-S apples during cold storage

The effects of 1-methylcyclopropene (1-MCP) on the fruit quality and antioxidant activity of ruby-S apples were evaluated during cold storage. The fruits were treated with 0 (control) and 1 μL/L 1-MCP and stored at 0°C for six months. The assessments were performed at 0 (harvest), 3, and 6 months of storage. Compared with the control, the 1-MCP-treated fruits exhibited a reduced internal ethylene concentration and slowed appearance of greasiness on the fruit skin. In addition, 1-MCP treatment helped maintain a reduction in flesh firmness, titratable acidity, and peel color attributes (L* and b*) of the fruit. However, 1-MCP treatment did not affect fruit weight loss, soluble solids content, or peel color a* value. The 1-MCP treatment helped delay the reduction in total phenolics (TPC) and total flavonoids (TFC) content as well as total antioxidant determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (RSA) in the peel tissue. In the pulp tissue, 1-MCP affected only TPC, and not TFC or DPPH RSA. Overall, this study suggests that 1-MCP treatment helps maintain the desirable fruit quality attributes of ruby-S apples during ripening, but its effect on antioxidant activity depends on the tissue type (peel and pulp) of the fruit.

Timing of Ethylene Inhibition Affects Internal Browning and Quality of 'Gala' Apples in Long-Term Low Oxygen Storage.

The objective of this study was to evaluate the timing of ethylene inhibition with preharvest and postharvest 1-methylcyclopropene (1-MCP) treatments on internal browning and quality of ‘Gala’ apples in long-term low O2 storage. ‘Gala’ apples were obtained from the same commercial orchard during their harvesting period for 2 years of study. Preharvest 1-MCP orchard spray (3.8% a.i) was applied at the label rate of 60 g 1-MCP per acre in the first year. Postharvest 1-MCP (1 μl L−1) treatments were made for 24 h at 0.5°C either at harvest time (1 day after harvest) or after storage in controlled atmosphere (CA) in both years. Apples were stored in 1.5 kPa O2 + 0.5 kPa CO2 or 0.6 kPa O2 + <0.5 kPa CO2 for 9 months in the first year and 1.5, 1.0, or 0.5 kPa O2 + 0.5 kPa CO2 for 8 months in the second year. Storage regimes with O2 concentrations less than 1 kPa were based on fruit respiration using SafePod™ technology. After removal from storage, all apples were then evaluated for internal browning and other quality attributes after 1, 7, and 14 days at room temperature (RT, 21–22°C). Internal browning developed in ‘Gala’ apples during both years of study, with up to 16% incidence across treatments in the first year and up to 84% in the second year. Apples stored in 0.5–0.6 kPa O2 had significantly less internal browning during both years of study, compared to apples stored in higher O2. The effect of 1-MCP on internal browning was negligible in 0.5–0.6 kPa O2 storage. ‘Gala’ stored in 1.5 kPa O2 and treated with postharvest 1-MCP after storage had significantly less internal browning with preharvest 1-MCP than those without preharvest treatment. Apples treated with postharvest 1-MCP at harvest time, instead of after storage, did not exhibit this same effect. Preharvest 1-MCP-treated fruit maintained greater firmness retention than those without preharvest 1-MCP, and this effect was further enhanced when 1-MCP was applied after storage. Postharvest 1-MCP had no effect on firmness retention in fruit without preharvest 1-MCP, but lower O2 maintained greater firmness in those apples. Preharvest 1-MCP had no significant effect on internal ethylene concentration, whereas it was reduced by postharvest 1-MCP at harvest time in the first year of study, regardless of storage regimes. However, internal ethylene was only affected by storage regime in the second year, with lower concentration in fruit from 0.5 kPa O2 than in those from higher O2. Greasiness developed only in the second year and postharvest 1-MCP consistently reduced it, regardless of treatment timing and storage regime. There was no greasiness in apples treated with postharvest 1-MCP at harvest and then held in 0.5 kPa O2 for 8 months plus 14 days at room temperature. Soluble solids concentration and malic acid content were slightly higher in ‘Gala’ apples with preharvest 1-MCP compared to those without, whereas there was little and inconsistent effect of postharvest 1-MCP on these attributes. Overall, storage regimes with less than 1 kPa O2 provided the least amount of internal browning and best quality attributes. Ethylene inhibition provided further benefits, but this was dependent on the timing of 1-MCP treatment.

Fruit Quality Attributes of ‘Arisoo’ and ‘Picnic’ Apples as Influenced by 1-Methylcyclopropene Concentration and Its Application Frequency during Cold Storage

The efficacy of 1-methylcyclopropene (1-MCP) in maintenance of apple fruit quality can differ depending on apple cultivar, ethylene content at harvest, 1-MCP concentration, the interval between harvest and 1-MCP application, and the number of applications. In this study, we investigated whether the 1-MCP concentration and its application frequency differently affected fruit quality attributes of the two new apple cultivars ‘Arisoo’ and ‘Picnic’. The fruits were treated with 1-MCP (as single or double treatments) at the rate of 0 μL L−1 (control), 0.5 μL L−1, 1 μL L−1, 0.5 + 0.5 μL L−1, and 1 + 1 μL L−1 for 18 h, and they were stored at 0 °C up to six months. Comparatively, the fruit qualities of 1-MCP treated fruits were higher than that of the control during cold storage, with a higher suppression of internal ethylene content and a slower reduction of titratable acidity in 1-MCP treatments than the controls throughout the cold storage in both cultivars, regardless of the concentration and number of applications. Reduction of fruit firmness and soluble solid contents were maintained by single application of 0.5 μL L−1 1-MCP in ‘Arisoo’ apple, while double application of 0.5 + 0.5 μL L−1 was needed in ‘Picnic’ cultivar. The effective concentration for weight-loss reduction was found to be the single application of 1 μL L−1 1-MCP in both ‘Arisoo’ and ‘Picnic’. Conclusively, 1-MCP as single treatment at the rate of 0.5 μL L−1 could be sufficient in inhibiting ethylene action and maintaining fruit quality losses during cold storage, particularly in ‘Arisoo’. However, double application of 1-MCP might be necessary for some quality attributes in ‘Picnic’ apple.