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Zhiguo Ju and Eric A. Curry

Effects of Lovastatin treatment on ethylene production, α-farnesene biosynthesis, and scald development were studied using `Delicious' and `Granny Smith' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] and `d'Anjou' pears (Pyrus communis L.) stored in air at 0 °C. During 6 months storage, Lovastatin did not affect internal ethylene concentration but reduced α-farnesene production in a concentration dependent manner in both apples and pears. Lovastatin reduced scald at 0.63 mmol·L-1 and inhibited scald completely at 1.25 or 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. In `d'Anjou' pears, Lovastatin at concentrations from 0.25 to 1.25 mmol·L-1 inhibited scald completely. After 8 months storage, inhibition of scald in both apples and pears by Lovastatin was concentration-dependent but none of the concentrations totally eliminated scald. Compared with 11.8 mmol·L-1 diphenylamine, Lovastatin treatment reduced scald to the same level at 1.25 mmol·L-1 in `d'Anjou' pear and 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. Lovastatin did not affect apple or pear fruit color, firmness, soluble solids content, or titratable acidity during storage in either apple or pear compared with the controls. Chemical name used: [1S-[1a (R °), 3α, 7β, 8β (2S °, 4S °), 8αβ]]-1,2,3,7,8,8α-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1-naphthaienyl 2-methylbutanoate (Lovastatin).

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Sylvia M. Blankenship, Michael Parker, and C. Richard Unrath

`Fuji' apples (Malus domestica Borkh.) were harvested at three maturities for three consecutive seasons. Fruit firmness, soluble solids concentration, starch—iodine index (SI), and internal ethylene concentration were measured at harvest. Fruit were stored in 0 °C air storage for 8 months. Fruit firmness and other maturity indices were measured monthly during storage. Using a stepwise regression procedure, harvest maturity indices were used to predict firmness after air storage. When all maturity indices measured were represented in the model, R 2 = 0.29, 0.34, and 0.26 at 4, 6, and 8 months, respectively. Use of only SI and fruit firmness in the model gave R 2 values of 0.25, 0.29, and 0.24 for 4, 6, and 8 months, respectively. Although R 2 values were low, they were highly significant. The model using fruit firmness and SI resulted in the best fit. Thus, an equation was developed using months of air storage, firmness, and SI at harvest. Actual firmness values correlated fairly well with predicted firmness values, usually within ≈5 N. On Washington apples, predicted values were 4.3 and 3.7 N too low compared to actual firmness values after 3 or 5 months' storage. In 1993, when predicted and actual firmness values were compared for Pennsylvania apples, predicted values ranged from 2.6 to 8.3 N too high after 3 months' storage, depending on harvest date. In 1994, Pennsylvania fruit stored 4 months had predicted values 0.5 N too high to 6.3 N too low, depending on harvest date. It may be possible to develop and refine models for an apple variety that would be applicable to several regions.

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S.R. Drake, T.A. Eisele, M.A. Drake, D.C. Elfving, S.L. Drake, and D.B. Visser

This study was conducted over three crop seasons using 'Delicious' (Scarletspur strain) apple trees on MM.111 rootstock. The bioregulators aminoethoxyvinylglycine (AVG) and ethephon (ETH) were applied alone or in combinations at various time intervals before harvest. Fruit response to bioregulators was evaluated at harvest and after storage. AVG applied 4 weeks before first harvest retarded starch loss at harvest, retained greater firmness, and reduced internal ethylene concentration and watercore of fruit at harvest and after both regular and controlled atmosphere storage. AVG did not influence peel color (hue values), but the flesh color of treated apples was more green. AVG in all instances tended to reduce the sensory scores for apples and apple juice. In contrast, ETH enhanced starch hydrolysis, flesh color development (green to more yellow), and soluble solids concentration while reducing titratable acidity levels. ETH had no influence on fruit firmness at harvest, but reduced firmness levels after storage in an inverse relationship to the concentration applied. Sensory values for whole apples were not influenced by ETH treatment, but ETH improved sensory preference for apple juice, particularly at early harvest. Applying AVG before ETH enhanced soluble solids and sensory scores for both fruit and juice. Treating with AVG followed by ETH at 150 mg·L–1 permitted the maintenance of satisfactory firmness values (>53.4 N) after long-term storage along with better quality and sensory perceptions. Using specific combinations of both AVG and ETH permitted ETH-mediated improvements in objective and perceived fruit quality to be obtained without the losses in flesh firmness and storability due to uncontrolled ethylene evolution and ripening typically observed when ETH is applied alone preharvest.

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Valeria Sigal-Escalada and Douglas D. Archbold

Our goal was to determine how aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (MCP) interact to influence postharvest storability and volatile production of `Gala' apple. In 2004 and 2005, AVG was applied to `Gala' apple trees 4 weeks before harvest. After harvest, control and AVG-treated fruit were treated for 20 h at 30 °C with MCP, and fruit were ripened at ambient temperature immediately after harvest, after MCP treatment, or after storage at 4 °C for 6 and 12 weeks. For both seasons, control fruit reached the highest internal ethylene concentration (IEC) during ripening at ambient temperature immediately after harvest. After storage, control fruit had very low IEC in 2004, but the highest in 2005. In general, the combined treatment repressed ethylene production the most for all harvest dates and lengths of storage. AVG plus MCP-treated fruit consistently had the highest flesh firmness (FF) but also had the lowest total volatile production (TVP) by flesh or peel after 6 and 12 weeks in cold storage following both harvest dates. The activity of alcohol acyltransferase was affected by the treatments, but could not explain all the variation found in TVP. TVP was lower for flesh than peel of control and treated fruit, but feeding alcohol substrates to the fruit resulted in a significant increase in TVP, regardless of tissue type or treatment. The results indicate that the combination of AVG plus MCP maintained apple fruit FF in cold storage better than the treatments used alone, but also substantially reduced TVP. Substrate availability seemed to be the most limiting factor affecting TVP by flesh and peel of `Gala' apples treated with AVG plus MCP.

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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.

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Jennifer De Ell and Dennis Murr

A sprayable formulation of 250 μL·L-1 1-MCP and 1% oil adjuvant was applied to mature `McIntosh', `Empire', and `Delicious' apple trees 1 week prior to anticipated optimum harvest. Other spray treatments included: none, 1% oil adjuvant alone, and a formulation of 125 μL·L-1 1-MCP and adjuvant (`Empire' only). Unsprayed fruit were treated postharvest with or without gaseous 1-MCP (1 μL·L-1). At harvest, internal ethylene concentration (IEC), starch index, firmness, and soluble solids concentration were measured, as well as CO2, ethylene, and total volatile production of fruit samples over a 14-day period at 22 °C. Additional fruit samples for all preharvest and postharvest 1-MCP treatments were held 14 days at 22 °C and IEC and firmness measured for treatment efficacy. Fruit quality was assessed at 3 and 6 month storage intervals and over a 2-week ripening period at 22 °C. For all cultivars, the production rates of CO2, ethylene, and volatiles, as well as increases of IEC and decreases in firmness were inhibited or delayed by sprayable 1-MCP treatment. These effects were comparable to the postharvest 1-MCP treatment and were maintained during storage. The results of these experiments suggest that sprayable 1-MCP could be an additionaal tool for maintaining apple fruit quality. However, the sprayable formulation used in this study caused 100% incidence of skin damage to `McIntosh' and a slight amount to `Empire' (<5%). Lesions were halo-like, centered around lenticels, and tended to be more severe near the calyx. No skin damage was observed in `Delicious' or in fruit treated with the adjuvant only or postharvest 1-MCP.

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Suparna Whale*, Zora Singh, and John Janes

The effects of preharvest application of AVG and ethephon alone, or in combinations, on color development, fruit quality and shelf life were tested in `Pink Lady' apples (Malus domestica Borkh.) in Western Australia during 2002.The experiment aimed at improving color without adversely affecting fruit quality at harvest and after long term cold storage. Treatments included 124.5 g·ha-1 AVG only [148 Days after full bloom (DAFB)]; 280 g·ha-1 ethephon only (148 DAFB); AVG (148 DAFB) followed by ethephon (166 DAFB); and control. Fruit were evaluated for color development, internal ethylene concentration (IEC) and quality at commercial harvest(181DAFB) and 45, 90, and135 days after cold storage (1 °C ± 0.5 °C). At harvest, ethephon with or without AVG significantly (P ≤ 0.05) improved red blush and total anthocyanin in fruit skin. AVG+ethephon treated-fruit had higher total anthocyanin and TSS compared to AVG alone and control fruit. There were no significant differences among different AVG and ethephon treatments for fruit firmness and IEC. During different storage periods, fruit treated with AVG alone and AVG+ethephon had significantly lower IEC compared to fruit treated with ethephon only and the control, however the interactions between treatments and storage periods were not significant for fruit firmness. AVG + ethephon and ethephon alone did not significantly affect fruit color during different storage periods, which showed that the subsequent ethephon spray on AVG-treated fruit had overcome the inhibitory effect of AVG. Our experimental results showed that application of AVG followed by ethephon improved color in `Pink Lady' apples without compromising fruit quality including firmness during extended cold storage.

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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.

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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.

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Morris Ingle, Mervyn C. D'Souza, and E.C. Townsend

Firmness, soluble solids concentration (SSC), starch index (SI), internal ethylene concentration (IE), and titratable acid concentration (TA) of `York Imperial' apple (Malus ×domestica Borkh.) fruit changed linearly with harvest date between 152 and 173 days after full bloom (DAFB). Firmness was positively correlated with TA, SSC was correlated with SI, and SI was negatively correlated with TA. After 150 days of refrigerated-air (RA) storage, there was no relationship between DAFB at harvest and firmness or superficial scald, but the malic acid concentration declined linearly and storage decay increased linearly with DAFB. Firmness had declined to a plateau and was not correlated with any variable at harvest. Malic acid concentration after CA storage was correlated with DAFB, firmness, SSC, and SI; scald was correlated with firmness and SI; and decay was correlated with DAFB, firmness, SSC, and SI. During 150 days of controlled-atmosphere (CA) storage (2.5% O2, 1.0% CO2), firmness and TA decreased as a linear function of DAFB. Percentage of fruit with scald and scald rating changed quadratically with DAFB, and decay increased linearly with DAFB. After 150 days of CA, firmness was correlated with DAFB, SI, and IE at harvest; TA was correlated with DAFB, firmness, SSC, TA, and SI; scald was correlated with firmness and SI; and decay was correlated with DAFB, SSC, and scald index at harvest. During 250 days of CA storage, firmness, TA, scald, and decay changed linearly with DAFB in only 1 or 2 years out of 3. Formulas were created to predict firmness after CA within 10 to 12 N (2.0–2.5 lb-f) and TA to within 25%.