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Christopher B. Watkins, William J. Bramlage, and Belinda A. Cregoe

To examine the hypothesis that superficial scald of apple (Malus domestics Borkh.) is a chilling injury, `Granny Smith' apples were stored at temperatures ranging from 0 to 20C, temperature-conditioned before storage, and warmed during storage. Fruit stored at 0 or 4C developed supeficial scald. At 10C, surface defects occurred but they were not typical symptoms of scald, and at 15 or 20C no symptoms developed. Accumulation of α-1 faroesene and conjugated trienes in fruit peel correlated with increasing ethylene production, which was greater at higher temperatures. However, concentrations of conjugated trienes were highest at 0 and 4C. When fruit were kept at 10C for 5 or 10 days before storage, scald development after storage was not reduced. An interruption of 0C storage with a single warming period at 10 or 20C reduced scald development after 25 weeks of storage, maximum reduction occurring when fruit were warmed for 3 to 5 days at 20C after 1 to 4 weeks at 0C. Amelioration of scald declined as time at 0C before warming increased. Diphenylamine application after the same intervals at 0C, instead of warming, also was less beneficial as time before treatment increased. α-Farnesene and conjugated trienes increased during warming, but at the end of storage (when scald was developing) the conjugated triene concentrations in peel were reduced in fruit that had been warmed. Warming slightly increased yellowing, softening, and greasiness of fruit after storage, We conclude that chilling induced superficial scald on `Granny Smith' apples.

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C. Chervin, J. Raynal, N. André, A. Bonneau, and P. Westercamp

The effects of ethanol vapors, controlled atmosphere (CA) storage, and a combination of both on superficial scald development on `Granny Smith' apples (Malus ×domestica Borkh.) are reported. The major result was that ethanol vapors, applied in cold storage, prevented scald development over a week at 20 °C in apples that had been CA-stored for 4 months, then left for 1 month in cold air storage. Interrupting CA storage aimed to reproduce industry practices when fruit in part of storage rooms has to be sold and the remaining fruit is held in air for later sale. The estimated cost and further development of this method are discussed.

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H.P.V. Rupasinghe, G. Paliyath, and D.P. Murr

α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the volatile components and the surface wax of apples (Malus ×domestica Borkh.). Although oxidation products of α-farnesene have been implicated in the development of superficial scald in apples, the relation between α-farnesene biosynthesis and scald development is not well understood. In vivo labeling studies using isolated tissue segments showed that α-farnesene is derived from trans,trans-[1,2-14Cor 1-3H]-farnesyl pyrophosphate (FPP) mostly in the skin rather than cortex tissue. Among other labeled products, farnesol was >100-fold higher compared to α-farnesene. However, HPLC analysis of hexane-extractable components from apple skin revealed farnesol is not a predominant natural constituent of apple skin tissue. In addition, trans,trans-[1-3H]-farnesol was not converted to α-farnesene by apple skin tissue. Our results indicate that biosynthesis of α-farnesene in apple tissue occurs through the isoprenoid pathway, and the conversion of FPP to α-farnesene is catalyzed by a single sesquiterpene synthase enzyme, trans,trans-α-farnesene synthase, rather than via farnesol as an intermediate. A comparison of α-farnesene biosynthesis between scald-developing and scald-free regions of the same apple showed that incorporation of radiolabel into α-farnesene from trans,trans-[1-3H]-FPP was nearly 3-fold lower in scald-developing skin tissue than in scald-free skin tissue.

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Eric A. Curry

Superficial scald is a physiological skin disorder of apples and pears that develops in cold storage and that often increases in severity after the fruit is removed. It is thought to be associated with the accumulation of farnesene in the epithelial tissue. Currently used methods of controlling scald are diphenylamine (DPA) drenches, and controlled atmosphere (CA) to a limited extent. In order to expand the methods available to control scald, we have been investigating the potential of a number of naturally occurring compounds applied to the fruit surface by drenching or by topical application. Fruit were treated either by wiping the fruit surface with technical-grade material and then removing the excess, drenching whole fruit in aqueous emulsions, or drenching fruit in combinations of heat plus emulsion. After treatment, the fruit was air-dried for 30 min and then placed either in regular or CA storage for 6 months, after which time they were placed in a dark room at 68F for 7 days. Scald was evaluated and fruit condition assessed. Results from 3 years indicate farnesene and squalene reduce scald in apples and pears.

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Jennifer R. DeEll, H.P. Vasantha Rupasinghe, and Dennis P. Murr

`Cortland' is an apple cultivar with inherent poor storeability because of excessive vulnerability to the development of superficial scald in long-term storage. The objectives of this investigation were to evaluate the potential of the potent ethylene action inhibitor 1-methylcyclopropene (1-MCP; EthylBloc®) to counteract this constraint and to develop some basic procedures for its exposure. Eight hours after harvest, fruit were exposed to 1.0 mL·L–1 1-MCP for 0, 3, 6, 9, 12, 16, 24, or 48 h at 3, 13, or 23 °C. Following exposure, fruit were placed at 0 to 1 °C in air for 120 days, after which time they were removed to 20 °C and held 7 days for post-storage assessment of ripening and to allow development of physiological disorders. In general, and within our experimental limits, the higher the temperature of 1-MCP exposure the shorter the required exposure time to obtain similar effects. The desired effectiveness of 1-MCP could be achieved by exposing fruit for at least 3 h at 23 °C, for 6 h at 13 °C, or for 9 h at 3 °C. 1-MCP-treated apples were consistently 2 kg firmer than untreated apples. Scald incidence in untreated fruit after 120 days at 0 to 1 °C and 7 days at 20 °C was 100%, whereas 1-MCP reduced scald by 95% in treatments of long enough duration at any particular temperature.

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Mulpuri V. Rao, Christopher B. Watkins, Susan K. Brown, and Norman F. Weeden

Fruit from seedlings selected from a population obtained by crossing superficial scald-resistant `White Angel' and superficial scald-susceptible `Rome Beauty' apple (Malus ×domestica Borkh.) were used to investigate the role of oxidative processes in the development of superficial scald. Selections were identified for study based on fruit coloration and scald susceptibility. Plant material had one of the following three physiognomies: 1) red-skinned fruit resistant to scald; 2) red-skinned fruit susceptible to scald; and 3) yellow-skinned fruit susceptible to scald. The concentrations of α-farnesene, conjugated triene (CT) species, hydrogen peroxide (H2O2), thiobarbituric acid-reactive substances, carbonyl groups, and the activities of superoxide dismutase, guaiacol-peroxidase, and catalase were measured at harvest and during 0.5 °C storage. Relationships were poor between scald susceptibility and α-farnesene and its oxidation products, CT258, CT281, and the CT258/CT281 ratio. Tissue concentrations of H2O2 were lower in scald-resistant than in scald-susceptible fruit at harvest and after storage, and these lower concentrations were associated with less damage to cellular membranes (lipid peroxidation) and proteins (carbonyl group content). Higher activities of the H2O2-degrading enzymes, guaiacol-peroxidases, and catalases, were related to lower H2O2 content and lower scald susceptibility. Activities of superoxide dismutase, a H2O2-generating enzyme, were not related to scald susceptibility or storage period. We hypothesize that fruit susceptibility to scald is strongly influenced by cellular efficiency in metabolizing active oxygen species such as H2O2.

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Paul M. Chen and Diane M. Varga

`D'Anjou' pears (Pyrus communis, L.) growing in 3 locations with the elevation at 150 meters, 380 meters, and 610 meters respectively in Hood River valley, Oregon were harvested at the commercial maturity with the flesh firmness of 62.3 Newton (±2.2 N) and stored in air at -1°C. Regardless of different growing elevations, the incidence of superficial scald became noticeable after 2.5 months of storage and became substantial after 3 months. The rate of scald development was higher on the fruit from 150 meters elevation than those from higher elevations. Alpha-farnesene and conjugated trienes in the peel tissue accumulated at faster and higher rates in the fruit from 380 meters and 610 meters elevations than those from 150 meter elevation. The threshold level of conjugated trienes which causes superficial scald disorder was different from the fruit grown at different elevations.

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Sunita Kochhar, Christopher B. Watkins, Patricia L. Conklin, and Susan K. Brown

The activities and isoenzyme patterns of guaiacol-dependent peroxidase (POX), ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase (CAT) were studied in yellow- and red-fruited crab apple [Malus (L.) Mill.] selections from a `White Angel' × `Rome Beauty' cross that show differential susceptibility to the physiological storage disorder, superficial scald. There were no consistent relationships between total enzyme activities and scald incidence, high activities of the enzymes being detected in selections with both high and low susceptibilities to scald. However, additional individual isoforms of some antioxidant enzymes were detected in the scald-resistant selections when compared with scald-susceptible selections. In a native gel system, four guaiacol-dependent POX isoenzymes were detected in both yellow and red scald-resistant selections compared with only two in scald-susceptible selections. Similarly, for anodic acidic POX assayed using benzidine, six isoenzymes were detected in both yellow and red scald-resistant selections compared with five in yellow and four in red susceptible selections. Ten SOD isozymes were detected in scald-resistant yellow-fruited selections compared with only five faint bands in scald-susceptible selections, but similar patterns were not detectable for red-fruited selections. Differences in the presence of various isoenzymes for CAT and APX were also detected among the selections, but associations with scald susceptibility were also affected by fruit color or were inconsistent. The presence or absence of individual isoenzymes may be a better indication of scald resistance or susceptibility than the total enzyme activities. Isoenzyme analyses, especially of POX, could be useful to breeders for the early detection of scald resistance/susceptibility in apples.

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Jinhe Bai

Superficial scald of `d'Anjou' pears usually develops after storage of 2 months or longer. MCP application controls scald; however, fruit lose their ripening capacity if the dosage is >30 ppb, but lower dosages cannot control scald substantially. In this study, fruit treated with or without 25 ppb MCP within 2 d after harvest were stored at –1 °C for up to 5 months. After 1, 7, 30, or 70 d of storage, part of the fruit were pulled from storage and treated with 1000 ppm ethoxyquin line spray and immediately returned to the storage, left untreated as non-ethoxyquin control. Incidence of superficial scald along with the concentrations of α-farnesene and conjugated trienes (CTs), and the ripening capacity of fruit were investigated after 3, 4, and 5 months storage. All fruit ripened properly within 7 d of conditioning at room temperature regardless of treatments. Both of MCP or ethoxyquin-1d (ethoxyquin was applied after 1 day storage at –1 °C) alone controlled scald for only 3 months; however, MCP + ethoxyquin controlled scald for 5 months, whenever ethoxyquin was applied between 1 to 70 d after storage. Thus, with 25 ppb MCP treatment, which is simple, with rapid and mass treatment available, a delayed application (up to 70 d) of ethoxyquin becomes effective to control scald. Furthermore, the later application of ethoxyquin within 70 d after MCP treatment, the less incidence of scald was observed. Scald is caused by the CTs oxidation products of α-farnesene. MCP and ethoxyquin inhibited accumulation of CTs of fruit peel by different mechanisms. MCP inhibited the production by influencing ethylene production through control of α-farnesene synthesis; however, ethoxyquin worked by inhibiting the oxidation of α-farnesene to the CTs.

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A.D. Bauchot, P. John, Y. Soria, and I. Recasens

Treatments were applied in Italy, United Kingdom, and Spain to test their effectiveness in controlling superficial scald in apples (Malus domestica Borkh.) after cold storage. In Italy where mature `Red Chief' and `Golden Delicious' were stored at 3-4C for 4 months, scald incidence was reduced by postharvest dipping in a sucrose-ester based coating, Semperfresh, formulated with the antioxidants, ascorbyl palmitate, and n-propyl gallate. In the United Kingdom and Spain, early harvested `Granny Smith' were stored at 0C for 4 and 6 months. In the United Kingdom, ascorbyl palmitate applied with Semperfresh significantly reduced scald upon withdrawal from 4 months of storage near 0C, but not after 10 days at room temperature. Bringing the apples to ambient temperature for 20 hours 1 month into cold storage reduced scald almost as much as diphenylamine application, but the beneficial effects seen after 4 months of cold storage did not persist after 6 months of storage. In Spain, controlled atmosphere storage (3% O2 + 3% CO2) was as effective as diphenylamine treatment, even after 6 months of storage; CaCl2 was slightly effective after 4 months of storage, but none of the coating treatments significantly reduced scald. Treatments applied after 6 weeks were ineffective.