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  • Author or Editor: Eric A. Curry x
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Within red cultivars, highly colored apples are often preferred. In addition to being esthetically more appealing. better color often indicates riper, better tasting fruit. Anthocyanin synthesis in apples is influenced by many external factors including light, temperature, nutrition, pruning, thinning, growth regulators, and bagging. Bagging is the practice of enclosing young fruitlets in several layers of paper to promote color development after the bag is removed in the fall before harvest. In experiments related to the temperature optimum of color development in various cultivars, bagging was used to produce fruit void of anthocyanins. Double layer paper bags (black-lined outer bag, red inner bag) were placed on `Akafu-1 Fuji', `Oregon-Spur Delicious', and the early coloring `Scarlet Spur Delicious' on June 21, 1993. Bags were not removed until fruit was taken to the lab on September 22 for both `Delicious' and `Fuji'. Whereas bagged `Fuji' apples were without red pigment, bagged `Delicious' sports showed considerable red pigment development, completely covering the apple in the case of the blush-type `Scarlet Spur' and showing streaks without pigment in the snipe-type `Oregon-Spur'.

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Present dietary recommendations for fruits and vegetables should be based on the bioavailability of essential nutrients at the time of optimum harvest. Few people, however, are fortunate enough to have available freshly harvested produce all year. With the development of improved postharvest technology, shelf life has increased dramatically in many parts of the world. How does the nutritional quality of fruits and vegetables change with increasing storage time, changes in storage atmosphere, different postharvest processes? Do these changes have an impact on dietary recommendations? Apples are capable of being stored for up to 12 months with properly managed temperature and storage atmosphere. Because information regarding this subject is lacking for apple (and many other fruits and vegetables), perhaps a model can be developed based on work with other commodities to help us understand the nutritional changes associated with different postharvest treatments.

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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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Warm daytime and cool nighttime temperatures during fruit maturation are conducive to anthocyanin synthesis and starch degradation in many apple cultivars. In parts of the world, high temperatures during fruit maturation result in sunburn of varying degrees of severity ranging from slight bleaching of the pigments in the epidermal layer to cracked and desiccated skin. This experiment assessed the effects of sunburn on fruit quality and mineral nutrition at harvest. In September 1990, about 2000 `Granny Smith' or `Delicious' apples were examined for sunburn and sorted into the following categories: none, light, bleached, bronzed, buckskin, and cracked. Twenty fruit were collected for each category. Each fruit was subdivided into exposed and shaded halves. Each half of each fruit was evaluated for firmness, soluble solids, and acidity. Tissue samples were analyzed for sugars, total nitrogen, and mineral content. Data suggest that excessive heat due to solar radiation creates a gradient of sugars and minerals within the fruit resulting in increased disorders in certain areas of the fruit.

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Abstract

The use of chemicals to control vegetative growth of fruit trees at the Tree Fruit Research Laboratory in Wenatchee, Wash, began 25 years ago. Vegetative growth of apple seedlings in greenhouse trials was first controlled with foliar applications of butanedioic acid mono (2,2-dimethylhydrazide) (daminozide) (B-9, Alar). Field trials then were conducted on both apple and young cherry trees (3, 4). Daminozide also has been used to improve annual return blooming and fruit set, promote red skin color development, delay maturity, and improve storability of apple cultivars. Often, the high rates needed to control vegetative growth have reduced fruit size and fruit length, resulting in flat fruit shape (4, 13, 28). The latter phenomenon is important, for ‘Delicious’ apple for which “typiness” is a strong marketing characteristic and therefore an economic benefit. This paper presents results of continuing research on the control of excessive vegetative growth of deciduous fruit trees.

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CPPU was applied to whole spur `Delicious' apple (Malus domestica Borkh.) trees in central Washington at 0,6.25,12.5,25, or 50 mg·liter-1 at full bloom (FB) or FB plus 2 weeks. At both application times, the flesh firmness of treated fruit linearly increased with increasing concentration. CPPU applied at 0,5,10,15, or 20 mg·liter-1 to spur `Delicious' trees in Massachusetts at king bloom resulted in a linear increase in flesh firmness at harvest and following 28 weeks in air storage at 0C. CPPU did not affect the incidence of senescent breakdown, decay, or cork spot. Fruit length: diameter (L/D) ratios generally increased at all doses. Fruit weight was not influenced at either location. All CPPU concentrations reduced return bloom on `Delicious' apples in Massachusetts in 1989. Of the 10, 20, or 40 mg·liter-1 treatments for `Empire' apples, only CPPU at 40 mg·liter-1 reduced return bloom. CPPU applied to `Empire' apples in Massachusetts did not effect fruit set, soluble solids concentration, L/D, or firmness; however, fruit weight increased linearly with concentration. CPPU applied at 100 mg·liter-1 retarded preharvest fruit drop of `Early McIntosh' in Massachusetts for ≈7 days but was not as effective as NAA at 20 mg·liter-1. In a larger semicommercial trial, `Delicious' fruit treated with CPPU at 5,10, or 15 mg·liter-1 at FB, petal fall (PF), or PF plus 1 week, respectively, were harvested and graded over a commercial packing line. Malformities caused by CPPU at the highest doses reduced packout, although all CPPU application rates reduced the percent fruit culled due to poor color. CPPU increased packed fruit size, since the size of fruit (64 mm in diameter) in the >150-fruit/box size decreased, while the size of fruit (72 mm in diameter) in the 100- and 130-fruit/box sizes increased. Treated fruit stored for 7 months at 1C were firmer than nontreated controls. Chemical names used: N-(2-chloro-4-pyridyl)- N' -phenylurea (CPPU); 1 naphthalene-acetic acid (NAA).

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`Granny Smith' apples (Malus × domestica Borkh) and `d'Anjou' pears (Pyrus communis L.) were dipped in a 2.5%, 5%, or 10% stripped corn oil (α-tocopherol <3 mg·kg-1) emulsions, 2000 mg·L-1 diphenylamine (DPA), respectively, at harvest and stored in air at 0 °C for 8 months. Untreated fruit served as controls. In oil-treated apples and pears, ethylene and α-farnesene production rates were lower in early storage and higher in late storage than in control. Control fruit developed 34% scald in `Granny Smith' apples and 23% scald in `d'Anjou' pears after 6 months storage, whereas fruit treated with oil at 5% or 10%, or with DPA at 2000 mg·L-1 were free from scald. After 8 months storage, oil at 10% was as effective as DPA in controlling scald in pears, whereas in apples, fruit treated with 10% oil developed 18% scald and DPA-treated fruit were scald-free. DPA-treated apples developed 32% senescent scald, while 5% or 10% oil-treated fruit had none. Oil-treated fruit were greener, firmer, and contained more titratable acidity after 8 months of storage than control or DPA-treated apples and pears. In `Granny Smith', 100% of the controls and 79% of the DPA-treated fruit developed coreflush after 8 months of storage, but both 5% and 10% oil-treated fruit were free from coreflush. In `d'Anjou', 34% of the controls and 27% of the DPA-treated fruit showed decay after 8 months of storage, compared with 5% decay in 5% oiltreated fruit, and no decay in 10% oil-treated fruit.

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Effects of Lovastatin treatment on ethylene production, α-farnesene biosynthesis, and scald development were studied using `Delicious' and `Granny Smith' apples and `d'Anjou' pears stored in air at 0 °C. During 6 months of 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 of storage, the inhibition of scald in both apples and pears by Lovastatin was concentration-dependent, but none of the concentrations eliminated scald. Compared with 11.8 mmol·L-1 diphenylamine (DPA), 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. Compared to the controls, Lovastatin did not affect fruit color, firmness, soluble solid contents, or titratable acidity during storage in either apple or pear.

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