A 2-year study was conducted in a ‘Golden Delicious’ (Malus ×domestica Borkh.) orchard with a high incidence of physiological fruit russeting to examine the effect of gibberellin A4+7 (GA4+7) on apple epidermal cell size. Beginning at petal fall, four sequential applications of GA4+7 (0, 15, or 30 mg·L−1) were applied to whole trees every 7–10 days with an orchard air-blast sprayer at a volume of ≈1000 L·ha−1. Fruit epidermal tissue samples were taken approximately monthly beginning 1 week after the fourth application. Tissue was treated in the laboratory with an enzyme mixture to remove cellular debris in preparation for examination using either light or scanning electron microscopy (SEM). In 2007, because russeting was insignificant, treatment differences could not be established. Moreover, transillumination microscopy did not permit accurate measurement of ‘Golden Delicious’ fruit epidermal planar cell area beyond midseason because the isolated cuticle became thick and multilayered. In 2008, however, respective treatments of 15 and 30 mg·L−1 reduced calyx end russeting by 40% and 83% and increased epidermal planar cell density by 14% and 27% as measured using SEM.
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.
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.
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'.
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.
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.
The cuticle is a complex organ. As the first line of defense for apple fruit, its main function is to protect cells from desiccation. It begins developing within several weeks of anthesis and continues responding to environmental conditions until the underlying tissue becomes necrotic. The physicochemical properties of the cuticle differ with cultivar and stage of development but are thought to be composed of carbohydrate fibers extending from the cell wall or the aqueous apoplast. If the latter is true, these fibers could allow contact or exchange with the environment through the lipoidal cuticle matrix. This visual report is the result of an examination of the substructure of the apple cuticle using scanning electron microscopy. These high-resolution micrographs suggest a transcuticular continuum exist in the form of tubular fibers.
In `Delicious' and `Granny Smith' apples, fruit did not produce α-farnesene until internal ethylene reached about 1 μL•L-1. The correlation between internal ethylene and α-farnesene production was highly significant (r2 = 0.71 and 0.76, respectively) and fitted the exponential growth equation. Aminoethoxyvinylglycine (AVG) inhibited both internal ethylene and α-farnesene production, while ethephon stimulated them. When applied to discs from preclimacteric fruit peel, cycloheximide and actinomycin D inhibited ethylene and α-farnesene production. In discs from AVG-treated fruit, ethephon induced α-farnesene synthesis. Cycloheximide, actinomycin D, and silver ion counteracted the stimulation effect of ethephon. When added to discs from preclimacteric fruit peel or AVG-treated fruit peel, hydroxymethylglutarc acid, mevalonic acid lactone, and farnesyl pyrophosphate induced α-farnesene synthesis, which was not affected by cycloheximide or actinomycin D.