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Chris B. Watkins* and Jacqueline F. Nock

Most information about the effects of 1-methylcyclopropene (1-MCP) on apple fruit that is available in the literature involves its application immediately after harvest. However, depending on the storage facility, fruit may be treated within a few days of harvest, especially if destined for rapid CA storage, or after longer time periods. We have investigated the effects of: 1) 1, 2, 3, 4, 6, and 8 d delays before 1-MCP treatment on `McIntosh', `Cortland', `Jonagold', `Empire' and `Delicious' apple quality stored in air for 2 and 4 months, and in CA for 4 and 8 months; and 2) 1, 7, 14, and 21 d delays on `Cortland', `Jonagold', `Empire' and `Delicious' apple quality stored in CA for 5 months. `McIntosh' and `Empire' apples were harvested at two maturities. Our data show that responses of apple cultivars to 1-MCP can be affected by delay treatments, but that within each cultivar, these effects vary according to harvest maturity, storage type, and length of storage.

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Christopher B. Watkins and Jacqueline F. Nock

The effects of temperature during 1-MCP treatment, and the effects of delays of up to 8 d after harvest before treatment, have been investigated using `Cortland', `Delicious', `Jonagold', and `Empire' (normal and late harvest) apple [(Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] cultivars stored in air for 2 and 4 months and in controlled atmosphere (CA) storage for 4 and 8 months. Fruit were treated with 1 μL·L–1 1-MCP for 24 hours on the day of harvest (warm) or after 1, 2, 3, 4, 6, or 8 days at cold storage temperatures. CA storage was established by day 10. Little effect of temperature during treatment (warm fruit on the day of harvest compared with cold fruit after 24 hours of cooling) was detected. Major interactions among cultivars, handling protocols before 1-MCP treatment, storage type and length of storage were observed. Delays of up to 8 days before 1-MCP treatment either did not affect efficacy of treatment, or markedly reduced it, depending on cultivar, storage type and length of storage. The results indicate that, depending on cultivar, the importance of minimizing the treatment delay increases as storage periods increase.

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Christopher B. Watkins and Jacqueline F. Nock

‘Honeycrisp’ is an apple [Malus xsylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] that can be stored in air for several months, but the flavor becomes bland with prolonged storage. Controlled-atmosphere (CA) storage recommendations have not been made in some growing regions, however, because of the susceptibility of fruit to physiological disorders. In the first year of this study, we stored fruit from six orchards in O2 partial pressures (pO2) of 1.5, 3.0, and 4.5 kPa with 1.5 and 3.0 kPa pCO2. In the second year, we stored fruit from three orchards in three storage regimes (2.0/2.0, 3.0/1.5, 3.0/0.5 kPa O2/kPa CO2) with and without treatment of fruit with 1-methylcyclopropene (1-MCP) at the beginning and end of the conditioning regime (10 °C for 7 days) that is commercially used for ‘Honeycrisp’. CA storage had little effect on flesh firmness, soluble solids concentration (SSC), and titratable acidity (TA) over the range of pO2 and pCO2 tested. Greasiness was generally lower in fruit stored in lower pO2 and higher pCO2. Susceptibility of fruit to core browning and senescent breakdown varied between years, but a high incidence of internal CO2 injury in fruit from some orchards occurred in both years. 1-MCP treatment decreased internal ethylene concentration (IEC) and sometimes maintained TA but had little effect on firmness and SSC. Senescent breakdown and core browning incidence were reduced by 1-MCP treatment where orchard susceptibility to these disorders was high. However, 1-MCP treatment sometimes increased internal CO2 injury, especially if treatment occurred at the beginning of the conditioning period. CA storage cannot be recommended for storage of New York-grown ‘Honeycrisp’ apples until management of CO2 injury can be assured.

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Fanjaniaina Razafimbelo, Jacqueline F. Nock and Chris B. Watkins

The ethylene inhibitor, 1 methylcyclopropene (1-MCP), is used extensively in New York to maintain quality of the `Empire' apple cultivar through the marketing chain. However, the cultivar is susceptible to external CO2 injury, a physiological disorder that develops predominantly on the unblushed area of the apple skin. Injury is expressed as tan colored, smooth, water-soaked areas that become irregularly shaped, rough, depressed and wrinkled. The disorder usually occurs during controlled atmosphere (CA) storage. 1-MCP may increase susceptibility of fruit to external CO2 injury. Three experiments have been carried out to investigate postharvest manipulations that may attenuate the effects of 1-MCP on external CO2 injury of `Empire' apple. 1) The effect of CO2 concentration (1%, 2.5%, and 5%) and time of exposure to 2.5% and 5% CO2 during CA storage. 2) Delaying exposure of fruit to 5% CO2 after harvest to up to 14 d. 3) Using lower concentrations of diphenylamine (DPA), an antioxidant that is known to eliminate susceptibility at normal rates. The results show that higher external CO2 injury levels are associated with higher CO2 concentrations, but that 1-MCP does not increase the exposure period of susceptibility to injury during CA storage. Susceptibility to CO2injury is decreased markedly by delaying application of CA storage in untreated fruit. In contrast, high susceptibility to injury is maintained in 1-MCP-treated fruit as long as 14 days after harvest. DPA eliminated injury in 1-MCP-treated fruit, even at 250 ppm, 25% of commercial rates used for superficial scald control. Our data show that 1-MCP increases susceptibility of `Empire' apples to external CO2 injury and special care is therefore required to avoid fruit losses. Nonchemical means may reduce losses, but the only technology that has been shown to eliminate risk of injury is DPA treatment.

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Chris B. Watkins, Juan-Pablo Fernández-Trujillo and Jacqueline F. Nock

Susceptibility of apple fruit to CO2 can be affected by cultivar and postharvest treatment with diphenylamine (DPA). To study possible metabolic reasons for CO2 injury development, `Cortland' and `Law Rome' apple fruit were either untreated or treated with DPA at harvest, and then exposed to air or 45 kPa CO2 for up to 12 days. Fruit were sampled at 3-day intervals during treatment, and peel and flesh samples were taken for organic acid and fermentation product analysis. Additional fruit were removed to air and stored for 25 weeks for evaluation of injury. `Cortland' apple fruit had more external CO2 injury, but less internal CO2 injury than `Law Rome'. DPA treatment markedly reduced incidence of both external and internal injury. Fermentation products increased in peel and flesh of both cultivars with increasing exposure to CO2. However, acetaldehyde concentrations were ≈10 times higher in peel and flesh of `Law Rome' than `Cortland' apples. Ethanol concentrations in the flesh were similar in both cultivars, but were about twice as high in `Cortland' than `Law Rome' peel. Neither acetaldehyde nor ethanol concentrations were affected consistently by DPA treatment. Cultivar or DPA treatment did not affect accumulation of succinate, often regarded as the compound responsible for CO2 injury. These results do not indicate that acetaldehyde, ethanol, or succinate accumulation is responsible for CO2 injury in apple fruit.

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J. Pablo Fernández-Trujillo, Jacqueline F. Nock and Christopher B. Watkins

`Cortland' and `Law Rome' apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] were either nontreated or treated with the inhibitor of superficial scald development, DPA, and exposed to air or CO2 (40 or 45 kPa) in air at 2 °C for up to 12 days. Fruit exposed to air or 45 kPa CO2 were sampled during treatment, and peel and flesh samples taken for fermentation product and organic acid analyses. After treatment, fruit were air stored for up to 6 months at 0.5 °C for evaluation of disorder incidence. `Cortland' apples were most susceptible to external CO2 injury and `Law Rome' to internal CO2 injury. DPA treatment markedly reduced incidence of both external and internal injury. Fermentation products increased in peel and flesh of both cultivars with increasing exposure to CO2, but the extent of the increase was cultivar dependant. Acetaldehyde concentrations were about 10 times higher in peel and flesh of `Law Rome' than that of `Cortland' apples. Ethanol concentrations in the flesh were similar in both cultivars, but were about twice as high in `Cortland' than in `Law Rome' peels. Neither acetaldehyde nor ethanol concentrations were affected consistently by DPA treatment. Succinate concentrations, often regarded as the compound responsible for CO2 injury, increased with CO2 treatment, but were not affected by DPA application. Citramalate concentrations were reduced by CO2 treatment in `Law Rome' peel, but other acids were not consistently affected by CO2. Results indicate that acetaldehyde, ethanol or succinic acid accumulation are not directly responsible for CO2 injury in apples. Chemical name used: diphenylamine (DPA).

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J. Pablo Fernández-Trujillo, Jacqueline F. Nock and Christopher B. Watkins

Effects of 20 kPa CO2 treatments on concentrations of fermentation products, organic acids, and activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH), were measured in fruit of selected strawberry cultivars (Fragaria ×ananassa Duch. `Annapolis', `Cavendish', `Honeoye', `Kent', `Jewell', `Lateglow', and `NorthEast'). Acetaldehyde, ethanol, and ethyl acetate concentrations accumulated in CO2-treated fruit of `Honeoye' and `Kent', but not in `Cavendish' or `Annapolis'. The former two cultivars were classified as intolerant to high CO2 and the latter two as tolerant to high CO2. Activities of PDC and ADH were higher in CO2-treated than in air-treated fruit of the tolerant cultivars but not in the intolerant cultivars. Succinate accumulated in fruit of all cultivars, but concentrations were higher in the tolerant than in the intolerant cultivars. Results are discussed in relation to tolerance of fruit to CO2.

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Seok-Kyu Jung, Jacqueline F. Nock and Chris B. Watkins

Late-harvested apple fruit generally are less responsive to 1-MCP than early harvested fruit, but the effect of harvest date on these responses can vary greatly by cultivar. Little is known about the relationships between internal ethylene concentration (IEC) and responses of fruit to 1-MCP. We have investigated the effects of 1-MCP on `McIntosh', `Cortland', and `Empire' apples in two experiments. In the first, fruit of each cultivar were picked three to five times during the normal harvest season, untreated or treated with 1 μL·L-1 1-MCP, and stored in air. Fruit IEC and firmness were then measured at monthly intervals for 4 months. In the second experiment, fruit were harvested several times during maturation, and, at each harvest, fruit were categorized into groups based on their IEC (<0.5, 0.5–1.0, 1–10, 10–50, 50–100; and >100 μL·L-1), treated with 1 μL·L-1 1-MCP for 24 hours at room temperature, and stored in air. The IEC and firmness of each fruit was then measured at set intervals during storage. Increasing IECs were associated with declining effectiveness of 1-MCP, but the individual fruit study showed that, even in high-IEC fruit, there was an initial inhibition of IEC values during storage before the IECs increased. A Lower IEC at harvest indicated a longer delay before the IEC ultimately increased. Collectively, the data show that it should be possible to determine the response of fruit to 1-MCP based on their IEC.

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Fanjaniaina Razafimbelo, Jacqueline F. Nock and Chris B. Watkins

The `Empire' apple cultivar is susceptible to external CO2 injury, a physiological disorder that is expressed as tan-colored, smooth, watersoaked areas that become irregularly shaped, rough, depressed, and wrinkled. 1-Methylcyclopropene (1-MCP) may increase susceptibility of fruit to external CO2 injury during controlled atmosphere (CA) storage. We have investigated the effects of 1-MCP on external CO2 injury of `Empire' apple using several approaches. 1) Fruit were treated with 1%, 2.5%, and 5% CO2 during storage. Higher injury levels were associated with exposure to higher CO2 concentrations. 2) Fruit were exposed to 2.5% or 5% CO2 for 3-week periods throughout storage, otherwise being kept at 1% CO2. Most injury occurred in fruit treated with elevated CO2 during the first 3 weeks of storage, and 1-MCP did not extend the period of susceptibility to injury. 3) Exposure of fruit to CA with 5% CO2 after harvest was delayed for up to 14 days. Susceptibility to injury remained high during the delay in 1-MCP-treated fruit in contrast to untreated fruit. 4) Fruit were treated with 250, 500, and 1000 μL·L-1 diphenylamine (DPA), an antioxidant applied for control of superficial scald that is known to prevent susceptibility of fruit to CO2 injury at 1000 μL·L-1. The DPA eliminated injury in 1-MCP treated fruit, even at 250 μL·L-1. Our data show that 1-MCP increases susceptibility of `Empire' apples to external CO2 injury and extra care is therefore required to avoid fruit losses. Nonchemical means may reduce losses, but only DPA application has been shown to eliminate risk of injury.

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Chris B. Watkins, Jacqueline F. Nock and Tarek Wardeh

A sprayable formulation of 1-MCP (250 μL·L-1) and 1% oil adjuvant was applied to `McIntosh' and `Empire' apple trees 24, 14, and 7 days prior to anticipated optimum harvest dates (early, mid-, and late-spray timings, respectively), and fruit harvested sequentially over 2 to 3 weeks from this date. At harvest, internal ethylene concentrations (IEC), percentage of blush, starch indices, firmness, and soluble solids concentration (SSC) were measured, as well as ethylene production of fruit maintained for 7 days at 20 °C. Additional fruit were stored in air (0.5 °C) with or without postharvest 1-MCP treatment. Preharvest drop of `McIntosh' apples was also measured. Quality of these fruit was assessed at intervals for up to 4.5 months (`McIntosh') or 6 months (`Empire'). All spray timing resulted in marked delays of preharvest drop. For both cultivars, increases of IEC were inhibited or delayed by sprayable 1-MCP treatment, but effects on other maturity and quality factors were small. Ethylene production of treated fruit was lower than that of untreated fruit. The effects of sprayable 1-MCP on IEC and firmness were maintained during storage, but the longetivity of these effects was affected by cultivar, spray timing, and storage period. Postharvest application of 1-MCP further inhibited IEC and maintained firmness of the fruit during storage. These experiments show that sprayable 1-MCP may be a valuable tool to manipulate both pre- and postharvest responses of apple fruit. However, with the formulation used in these experiments, phytotoxicity, primarily as damage around lenticel areas, was observed at harvest indicating that further development of the formulation is necessary for industry use.