`Potomac' has been released as a new pear cultivar which combines a high level of resistance to fire blight with excellent fruit quality. Selected from a cross of `Moonglow' × `Beurre d'Anjou', it was tested under the seedling number, US 62537-048. Fruit are ovate-pyriform in shape, and average 73mm in diameter. Skin color is light green and the finish is glossy at harvest maturity, which occurs about 2 weeks after `Bartlett'. Flesh texture is moderately fine, buttery, and juicy; grit cells are small and limited to a thin layer under the skin. Flavor is subacid, with mild aroma, and similar in character to `Beurre d'Anjou'. Fruit may be ripened after harvest without cold storage, but `Potomac' is more susceptible to superficial scald than Beurre d'Anjou if stored for more than eight weeks. The tree is moderately vigorous. Yield and precocity are moderate. Fire blight resistance is greater than that of `Seckel', with a high degree of resistance in both shoots and blossoms. The cultivar is recommended for home orchards and limited commercial trial.
Richard L. Bell, T. van der Zwet, C.K. Chandler, and J.C. Scheerens
Xuetong Fan, Luiz Argenta, and James Mattheis
`Bartlett' and `d'Anjou' pear fruit were treated after harvest with MCP at 0, 0.01, 0.1 or 1 mL•L-1 and then stored at 1 °C. After storage, half of the fruit was continuously exposed to 10 mL•L-1 ethylene for 7 days in a flow-through system at 20 °C. A treatment concentration effect was evident for both respiration and ethylene production, all MCP concentrations reduced respiration and ethylene production by `d'Anjou' and `Bartlett' fruit compared to controls. Fruit quality changes in `d'Anjou' and `Bartlett' fruit were delayed by MCP treatment. Firmness and titratable acidity were higher through 4 months storage for `Bartlett' fruit treated at the two higher MCP rates. After 2 months, `Bartlett' fruit treated at the two higher MCP rates remained green, but, after 4 months, all fruit were yellow. Loss of firmness and titratable acidity was also reduced following MCP treatment of `d'Anjou' fruit. Yellowing of `d'Anjou' fruit was prevented by MCP treatment, even when fruit were exposed to ethylene after removal from storage. Poststorage ethylene exposure did not overcome the effects of MCP. Development of superficial and senescent scald was prevented by MCP treatment.
J.P. Mattheis, D.A. Buchanan, and J.K. Fellman
Quantitative and qualitative changes in net production of volatile compounds by apples occurs during fruit development with a major transition to ester production occurring as fruit ripening begins. Ester production during fruit ripening is an ethylene-mediated response; however, differences in maturation patterns among apple cultivars led us to examine the relationship between ester production and onset of the ethylene climacteric in several commercial apple cultivars. Emission of volatile esters as a function of apple fruit development was evaluated for `Royal Gala', `Bisbee Delicious', `Granny Smith', and `Fuji' apple fruit during two harvest seasons. Apples were harvested weekly and analyses of harvest maturity were performed the day after harvest. Non-ethylene volatiles were collected from intact fruit using dynamic headspace sampling onto Tenax traps. Fruit from each harvest was stored at 1°C in air for 5 months (3 months for `Royal Gala') plus 7 days ripening at 20°C, then apples were evaluated for the development of disorders. The transition to ester production occurred after internal ethylene exceeded 0.1 μL for `Royal Gala', `Bisbee Delicious', and `Fuji'. Ester emission by `Granny Smith' apples remained low throughout the harvest period. Increased ester emission occurred after the optimum harvest date (as determined by the starch index and internal ethylene concentration) for controlled-atmosphere storage of `Bisbee Delicious' and prior to optimum maturity for `Royal Gala' and `Fuji'. A relationship between the potential for development of superficial scald and ester production at harvest was evident only for `Bisbee Delicious' apples.
Terence L. Robinson* and Christopher B. Watkins
In 2001 and 2002, we imposed a wide range of croploads (0-15 fruits/cm2 of TCA) on 4- and 5-year-old Honeycrisp/M.9 trees by manual hand thinning soon after bloom to define appropriate croploads that give adequate repeat bloom and also the best fruit quality. At harvest each year we evaluated fruit ripening and quality. Samples were stored for 5 months in air at 38 °F and 33 °F and evaluated for fruit firmness and storage disorders. Cropload was negatively correlated with tree growth, return bloom, fruit size, fruit red color, fruit sugar content, fruit starch content, fruit firmness, fruit acidity, fruit bitter pit, fruit senescent breakdown, fruit rot and fruit superficial scald, but was positively correlated with leaf blotch symptoms, fruit internal ethylene concentration at harvest, and fruit soggy breakdown. There was a strong effect of cropload on fruit size up to a cropload 7, beyond which there was only a small additional effect. Although there was considerable variation in return bloom, a relatively low cropload was required to obtain adequate return bloom. Fruit red color was reduced only slightly up to a cropload of 8 beyond which it was reduced dramatically. The reduced fruit color and sugar content at high croploads could indicate a delay in maturity of but, fruits from high croploads were also softer, had less starch and greater internal ethylene. It that excessive croploads advance maturity. Overall, croploads greater than 10 resulted in no bloom the next year, and poor fruit size, color and flavor, but these fruits tended to have the least storage disorders. Moderate croploads (7-8) resulted in disappointing return bloom and mediocre fruit quality. For optimum quality and annual cropping, relatively low croploads of 4-5 were necessary.
Richard L. Bell*, Tom van der Zwet, and Diane D. Miller
`Shenandoah' is a new European pear (Pyrus communis L.) cultivar which combines resistance to fire blight with fruit of excellent quality. The original seedling tree was selected in 1985 from a cross of `Max Red Bartlett'× US 56112-146, and was tested under the original seedling number, US 78304-057. The fruit of `Shenandoah' is pyriform in shape, and moderately large in size, averaging 72 mm in diameter and 92 mm in height. Skin color at harvest is light green, turning yellow-green when ripe. The skin finish is glossy, and 10% to 20% of the fruit surface is blushed red. There is light tan russet at the calyx. Lenticles are slightly conspicuous, and are surrounded by small, light brown russet. The stem is medium to long (≈25 mm), of medium thickness, and slightly curved. Harvest maturity occurs about four weeks after `Bartlett', and the fruit will store in refrigerated (-1 °C) air storage for at least four months without core breakdown or superficial scald. The flesh texture is moderately fine, juicy, and buttery. Grit cells are moderately small and occur primarily around the core and in a thin layer under the skin. The flavor is aromatic, similar to `Bartlett', and is moderately acidic during the first two months of storage, becoming subacid after longer storage. The tree is moderate in vigor on `Bartlett' seedling and `OHxF 97' rootstocks, and upright-spreading in habit. Shenandoah' blooms in mid-season, similar to `Bartlett'. Yield has been moderately high and precocious, and with no pronounced biennial pattern. Fire blight resistance is similar to `Seckel', with infections extending no further than 1-year-old branches. Artificial blossom inoculations indicate a moderate degree of blossom resistance to fire blight infection.
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.
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.
Richard L. Bell, T. van der Zwet, and R.C. Blake
`Blake's Pride' has been released jointly by USDA and The Ohio State Univ. as a new fire blight-resistant cultivar. The original seedling tree was selected in 1977 at the Ohio Agricultural Research and Development Center in Wooster by R.C. Blake and T. van der Zwet from a cross of US 446 × US 505, performed in 1965 by H.J. Brooks, and was tested under the original seedling number, OHUS 66131-021. The fruit of `Blake's Pride' is pyriform to round-pyriform in shape, and is moderate in size, averaging ≈2.75″ to 3″ in diameter, and 3.25″ in height. The stem is short, medium in thickness, and upright. Skin undercolor is yellow, the finish is glossy, and 20% to 30% of the fruit surface is covered with a smooth, light tan russet. Harvest maturity occurs about 3 weeks after `Bartlett', and the fruit will store in air storage for at least 3 months without core breakdown or superficial scald. The flesh texture is moderately fine, juicy, and buttery. Grit cells are moderately small and occur primarily around the core and in a thin layer under the skin, similar to `Bartlett'. The flavor is subacid and aromatic. The tree is moderate in vigor on `Bartlett' seedling rootstock, and upright-spreading in habit. Yield has been moderate to moderately high. Fire blight infections are rare, and extend no further than 1-year-old growth. Artificial blossom inoculations indicate a moderate degree of resistance of blossoms to fire blight infection. Resistance of `Blake's Pride' to both shoot and blossom infection is much greater than that of `Bartlett'.
John M. DeLong, Robert K. Prange, and Peter A. Harrison
`Redcort Cortland' and `Redmax' and `Summerland McIntosh' apples (Malus ×domestica Borkh.) were treated with 900 nL·L-1 of 1-methylcyclopropene (1-MCP) for 24 hours at 20 °C before storage and were kept at 3 °C in either a controlled atmosphere (CA) of 2 kPa O2 and <2.5 kPa CO2 or in an air (RA) environment for up to 9 months. After 4.5 months, half of the fruit were treated with a second 900 nL·L-1 1-MCP application in air at 3 °C for 24 hours and then returned to RA or CA storage. At harvest and following removal at 3, 6, and 9 months and a 7-day shelf life at 20 °C, fruit firmness, titratable acidity (TA) and soluble solids content (SSC) were measured, while internal ethylene concentrations (IEC) in the apple core were quantified after 1 day at 20 °C. Upon storage removal and following a 21-day shelf life at 20 °C, disorder incidence was evaluated. 1-MCP-treated apples, particularly those held in CA-storage, were more firm and had lower IEC than untreated fruit. Higher TA levels were maintained with 1-MCP in all three strains from both storages, while SSC was not affected. Following the 6- and/or 9-month removals, 1-MCP suppressed superficial scald development in all strains and reduced core browning and senescent breakdown in RA-stored `Redmax' and `Summerland' and senescent breakdown in RA-stored `Redcort'. 1-MCP generally maintained the quality of `Cortland' and `McIntosh' fruit held in CA and RA environments (particularly the former) to a higher degree than untreated apples over the 9-month storage period. A second midstorage application of 1-MCP at 3 °C did not improve poststorage fruit quality above a single, prestorage treatment.
James Mattheis and David Rudell
Metabolism of peel constituents was assessed during ripening of `Delicious' and `Golden Delicious' apples. The ethylene action inhibitor 1-methylcyclopropene (1-MCP) and/or controlled atmosphere storage (CA) were used to limit ethylene activity during and after storage at 1 °C. `Delicious' apples not exposed to 1-MCP developed a brownish discoloration (not superficial scald) during the initial 2 months of storage in air. LC/MS analyses of peel components indicated 1-MCP and/or CA inhibited the degradation of compounds responsible for red peel color (i.e., idaein) as well as other flavonoids. Ethylene regulation of metabolism of other phenolic and related constituents including (-)epicatechin and chlorogenic acid appears to be compound specific. The (-)epicatechin content is not impacted by 1-MCP or CA, while chlorogenic acid accumulation is reduced in fruit exposed to 1-MCP and/or stored in CA. β-carotene and lutein content in peel of `Delicious' fruit stored in air was lower compared with untreated controls. Chlorophyll degradation was enhanced in air-stored fruit previously exposed to 1-MCP; however, this result was not observed in 1-MCP exposed fruit from CA. Results for `Golden Delicious' apples also indicated that exposure to 1-MCP and CA, as well as storage duration, impacts metabolism of peel constituents. Chlorophyll degradation was delayed in fruit previously exposed to 1-MCP and then stored in CA. Impacts of 1-MCP and storage environment on concentrations of other `Golden Delicious' peel constituents increased with storage duration. The results indicate metabolism of apple fruit peel constituents during fruit ripening is differentially regulated by ethylene.