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`Golden Delicious' apple [Malus sylvestris var. domestica (Borkh.)] cortex disks suspended in solutions containing a nitric oxide (•NO) donor [S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP)], •NO gas, or nitrite (KNO₂) were used to identify impacts of •NO on ethylene production and NO₂ ^– on •NO and ethylene production. Treatment with GSNO or SNP reduced ethylene biosynthesis compared with control treatments containing equimolar concentrations of oxidized glutathione (GSSG) or Na₄(CN)₆ respectively. Apple disk exposure to •NO gas did not impact ethylene production. Treatment with NO₂ ^– resulted in increased •NO production and decreased ethylene biosynthesis. Generation of •NO increased linearly whereas ethylene generation decreased exponentially with increasing NO₂ ^– treatment concentration. •NO was enhanced in autoclaved tissue disks treated with NO₂ ^–, suggesting that its production is produced at least in part by nonenzymatic means. Although this evidence shows •NO is readily generated in apple fruit disks by NO₂ ^– treatment, and ethylene synthesis is reduced by •NO/NO₂ ^– generated in solution, the exact nature of •NO generation from NO₂ ^– and ethylene synthesis modulation in apple fruit disks remains to be elucidated.

Postharvest management of apple fruit ripening using controlled atmosphere (CA) storage can be enhanced because CA oxygen concentration is decreased to close to the anaerobic compensation point (ACP). Monitoring fruit chlorophyll fluorescence (CF) is a technology to assess fruit response to low pO₂ as fluorescence increases as pO₂ reaches a critically low concentration. This type of pO₂ management has been referred to as dynamic atmosphere storage (DCA). Use of very low pO₂ can enhance post-storage apple fruit quality for many cultivars, allowing better firmness retention and prevention of superficial scald, compared with fruit stored at higher pO₂ during CA. ‘Honeycrisp’ is a chilling-sensitive cultivar with little risk of firmness loss or superficial scald during storage; however, other aspects of fruit-quality loss during storage, including soluble solids content (SSC), titratable acidity (TA), peel greasiness, and physiological disorder development may be impacted by pO₂. A 2-year study was conducted to identify ‘Honeycrisp’ fruit-quality impacts of CA storage with a low-pO₂ setpoint determined by using CF. ‘Honeycrisp’ apples were held 7 days at 10 °C after harvest, then at 3 °C. An additional treatment with 1-methylcyclopropene (1-MCP) was conducted in year two. CA was established 48 hours after transfer to 3 °C. In both years, fruit CF increased when pO₂ decreased to ≈0.3 kPa O₂ and then decreased after pO₂ was increased to 0.5 kPa. Additional CA pO₂ concentrations above 0.3 kPa were also maintained for other fruit. Fruit internal disorder incidence increased as pO₂ decreased and with 1-MCP use. Changes in SSC, TA, and peel yellowing were inconsistently reduced by storage at lower pO₂. Peel greasiness did not develop in either year. CA did not impact the incidence of chilling disorders regardless of pO₂. Results indicate some aspects of ‘Honeycrisp’ fruit quality can be enhanced as CA pO₂ decreases; however, pO₂ above the low pO₂ threshold did not prevent internal physiological disorder development.

‘Honeycrisp’ apples are susceptible to develop the physiological disorder bitter pit. This disorder typically develops during storage, but preharvest lesion can also develop. ‘Honeycrisp’ is also chilling sensitive, and fruit is typically held at 10–20 °C after harvest for up to 7 days to reduce development of chilling injury (CI) during subsequent cold storage. This temperature conditioning period followed by a lower storage temperature (2–4 °C) reduces CI risk but can exacerbate bitter pit development. Bitter pit development can be impacted in other apple cultivars by the use of controlled atmosphere (CA) storage and/or 1-methylcyclopropene (1-MCP). Studies were conducted to evaluate efficacy of CA and/or 1-MCP to manage ‘Honeycrisp’ bitter pit development. Apples from multiple lots, obtained at commercial harvest, were held at 10 °C for 7 days and then cooled to 3 °C. Half the fruit was exposed to 42 μmol·L⁻¹ 1-MCP the day of receipt while held at 10 °C. Fruit were stored in air or CA (3 kPa O₂, 0.5 kPa CO₂ for 2 days, then 1.5 kPa O₂, 0.5 kPa CO₂) established after 1 day at 10 °C or after 7 days at 10 °C plus 2 days at 3 °C. Fruit treated with 1-MCP and/or stored in CA developed less bitter pit compared with untreated fruit stored in air, and bitter pit incidence was lowest for 1-MCP-treated fruit with CA established during conditioning. Development of diffuse flesh browning (DFB) and cavities, reported to occur during ‘Honeycrisp’ CA storage, was observed in some lots. Incidence of these disorders was not enhanced by establishing CA 2 days compared with 9 days after harvest. 1-MCP and CA slowed peel color change, loss of soluble solids content (SSC) and titratable acidity (TA), and reduced ethylene production and respiration rate. The results indicate potential for the postharvest management of bitter pit development in ‘Honeycrisp’ apple through use of 1-MCP and/or CA storage.

Recently there has been much progress in the development of technologies that use biomarkers to detect and manage postharvest physiological disorders for apples in long-term storage. Such technologies have the capacity to alleviate fruit loss by allowing storage operators to more effectively manage the disorder by adjusting stock distribution. The technology may also reduce costs for storage materials and associated management activities. However, as is common for many new technologies that have not yet been adopted commercially in agriculture, the net economic value of the technology is not well understood and is difficult to assess ex ante. In horticultural markets that include quality (and price) differentiated products, technologies that affect grading are expected to impact revenues in nontrivial ways. Here we develop a framework to assess the likely range of economic implications associated with the adoption of the biomarker technology that allows a greater share of fruit to be marketed in a higher grade and may influence the costs of storing fruit. Results indicate that 10% increases in the share of higher quality fruit lead to increased profits of between 0.99% and 3%. A scenario that leads to a 10% increase in the share of fruit in higher grades and a 10% decrease in material costs for storage would increase profits by ≈4.4%. Our analysis and results are specific to the case of biomarker use to manage postharvest disorders for ‘Empire’ [Malus sylvestris (L.) Mill var. domestica Borkh.] apples, yet the framework can be used with cultivar-specific price and yield information to assess the ex ante economic implications of adopting the technology more generally.

‘Royal Gala’ apples [Malus domestica (Borkh.) Mansf.]can develop postharvest disorders such as flesh browning, senescent breakdown, peeling, cracking, or shriveling during and after cold storage. The objective of this study was to examine the effects of storage temperature and a range (0, 0.25, 0.5, or 1 µL·L⁻¹) of 1-methylcyclopropene (1-MCP) concentrations on fruit quality attributes and incidence and severity of physiological disorders during and after cold storage. Storage temperature differentially affected internal ethylene concentration (IEC), fruit circumference, and cortex color. 1-MCP treatment resulted in significant effects on fruit quality attributes and severity of physiological disorders, regardless of storage temperature. Incidence and severity of diffuse flesh breakdown (DFB), shriveling, cracking, and peeling were highest in control fruit stored but radial stem-end flesh breakdown (RSFB) only primarily in 1-MCP-treated fruit. Incidence of RSFB was highest following storage at 0.5 °C compared with 3 °C. 1-MCP treatment had the most influence on disorder incidence/severity or quality attributes, while treatment concentration of 1-MCP was not significant. Overall, the results indicate that 1-MCP treatment can reduce the incidence of ‘Royal Gala’ DFB but may enhance sensitivity to RSFB, when fruit are stored at 0.5 or 3 °C. Incidence of DFB and RSFB are influenced differentially by storage temperature or by 1-MCP treatment, respectively, indicating they may be different disorders.

Repeated preharvest applications of methyl jasmonate (MJ) to 'Fuji' apple [Malus sylvestris var. domestica (Borkh.) Mansf.] fruit were evaluated for impacts on peel color, size, fruit finish, and maturation. MJ treatments at 2 week intervals began 48 days after full bloom (DAFB) (early season) or 119 DAFB (late season) and fruit were harvested 172 DAFB. MJ treatment stimulated significant increases in peel red color following the initial application and thereafter. Early season MJ treatment reduced fruit diameter and length to diameter ratio but slowed softening and starch hydrolysis. Fruit receiving late season MJ treatments had increased incidence of bitter pit and splitting, shorter green life, and slower softening. Results suggest preharvest application of MJ impacts apple color development and other aspects of fruit quality. Chemical name used: methyl 3-oxo-2-(2-pentenyl)cyclopentane-1-acetate (methyl jasmonate).

‘Royal Gala’ apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] fruit can be susceptible to the development of postharvest disorders such as flesh breakdown and cracking (splitting) during and after cold storage. The objective of this research was to investigate fruit size and 1-methylcyclopropene (1-MCP) treatment effects on fruit physiological attributes and incidence and severity of storage disorders in ‘Royal Gala’ apples held in cold storage. In 2011, fruit segregated at harvest into two groups based on size (120 to 175, 250 to 350 g/fruit) were stored in air at 0.5 °C for 6 months and then at 20 °C for 7 days. In 2012, fruit were sorted into four groups (less than 200, 200 to 240, 241 to 280, and greater than 280 g/fruit), treated with 0 or 1 μL·L⁻¹ 1-MCP for 12 hours, and then stored in air at 0.5 °C for 3 or 6 months. Storage disorders were only detected at 6 months, regardless of 1-MCP treatment. In both control and 1-MCP-treated fruit, flesh breakdown incidence increased with fruit size, whereas severity was less associated with size. The progression of flesh breakdown developed in overall cortex tissue of control fruit but only detected in the stem-end tissue of 1-MCP-treated fruit. Internal ethylene concentration (IEC) decreased and CO₂ production increased with increased fruit weight; however, 1-MCP-treated fruit had low IEC regardless of weight. Cortex tissue lightness (L*) increased with fruit size irrespective of tissue localization (stem end, equatorial, calyx end) at harvest. During 6 months’ storage, L* decreased with increased fruit size in controls but not 1-MCP-treated fruit. Fruit fresh weight loss increased with fruit size and storage duration, more so in controls when compared with 1-MCP-treated fruit. Furthermore, fruit circumference increased during storage with fruit size only for control fruit. These physical changes are associated with susceptibility of large fruit to flesh breakdown more so than small fruit. Reduced flesh breakdown incidence, progression of symptoms from the stem end into the cortex, and symptom severity in 1-MCP-treated fruit may indicate flesh breakdown is related to fruit ripening and senescence.

‘Royal Gala’ apples can be susceptible to the incidence of fruit cracking and senescent flesh breakdown during cold storage. Because the development of these physiological disorders in other cultivars can be influenced by humidity during storage, the objective of this study was to evaluate the effect of high storage humidity on fruit quality attributes and incidence of physiological disorders in cold-stored ‘Royal Gala’ apples. Fruit obtained from a commercial orchard were kept in cardboard boxes with or without a perforated polyethylene liner during and after cold storage. High storage humidity induced by the perforated polyethylene liner reduced fresh weight loss but enhanced the change of fruit circumference after cold storage. High storage humidity contributed the most reduction of cortex lightness (L*) and hue angle (h ^o) in stem-end cortex tissues during shelf life. Fruit stored with liners had reduced internal ethylene concentration (IEC) and outer cortex firmness after removal from storage compared with control fruit. Furthermore, high storage humidity prevented shriveling but provoked fruit cracking. The incidence and severity of flesh breakdown were further aggravated during shelf life, compared with cold storage, regardless of a liner application. Overall, maintaining high storage humidity by applying a perforated polyethylene liner can contribute to delaying fresh weight loss, reducing IEC, and preventing fruit shriveling but can enhance cortex tissue browning, loss of flesh firmness, and incidence of fruit cracking during cold storage and shelf life.

A distinct type of postharvest skin browning on apple (Malus domestica Borkh.) fruit called “stain” is a frequent disorder in ‘Fuji’ grown under high light and elevated temperatures. Symptoms typically develop only on sun-exposed sections of the fruit regardless of the presence of sunburn symptoms, and sometimes only in the margins of this area. The role of different antioxidant systems in tissue exposed to different levels of sunlight and having different degrees of sun injury were investigated during cold storage [1 °C, >90% (relative humidity) RH]. Ascorbic acid (AsA) and glutathione (GSH) concentrations, AsA–GSH recycling enzyme activities and gene expression, and flavonoids and carotenoid concentrations were determined every 30 days. “Stain” incidence increased with sun exposure and sunburn level. Both shaded and exposed fruit peel without sunburn symptoms had the highest AsA content. The AsA–GSH recycling enzyme activities and gene expression levels had no clear relationship with sun exposure during cold storage. Chlorophyll a (chl a) and chlorophyll b (chl b) levels diminished over time and were higher in tissue without any type of sun injury. In contrast, carotenoid levels increased as sun injury incidence increased and remained relatively stable during storage. Total phenolics and quercetin glycoside levels changed coincidently during storage. Results indicate that the AsA–GSH cycle does not have a clear role in “stain” development. Nevertheless, reduced ascorbate levels may reduce the capacity to prevent oxidative stress–provoked damage which may, in turn, result in oxidation of quercetin glycosides, which would then lead to skin browning.

The stigmatic secretions of pomaceous flowers serve as a natural medium not only for pollen, but also for the pathogen Erwinia amylovora (Burr.) Winslow et al. and other microorganisms. To understand the microecology on the stigma, exudates from cultivars of pear (Pyrus communis L.), apple (Malus pumila P. Mill.), and crab apple [Malus mandshurica (Maxim.) Kom.] were analyzed for free sugars and free amino acids as available carbon and nitrogen sources. Extracts were obtained at different stages of anthesis by submerging and sonicating stigmas in water. Certain free sugars (glucose and fructose) and free amino acids (proline, asparagine, glutamic acid, and glutamine) were consistently predominant and increased during anthesis. Apple stigma extracts were also analyzed for polysaccharides and proteins. Of major components identified for apple, free sugars made up 4.5% by mass; polysaccharides (composed of arabinose and galactose), 49.6%; and proteins, 45.9%. The two largest components are likely present as glycoproteins. This may be the first report on characteristics of rosaceous stigma exudates that includes the identity of specific free sugars, free amino acids, and polysaccharide subcomponents. Discussion includes the comparison of pomaceous stigma exudates to those of other plants and the microecological implications.