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During the last two decades, per capita consumption of fresh fruit has increased markedly. Although many believe that this increase has been caused by a heightened concern in health and diet, economic analyses indicates that changes in retail prices and increasing per capita incomes adequately explain the increased consumption of fresh fruit. Also, with more single households and women entering the labor force, the convenience factor of focal preparation has likely caused an increase in the consumption of fresh fruit. Substantial substitution between fresh fruit products has occurred: grapes and strawberries have increasingly substituted for citrus fruit, particularly grapefruit. These results suggest that relative prices for fresh fruits, increasing disposable income, and the changing demographic composition of households have prompted observed increases in the per capita consumption of fresh fruit.

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peel disorders are key factors affecting external fruit quality for fresh consumption. Different postharvest peel disorders have been described in citrus fruit. However, the responsible causes for many of them are not well understood, their incidence

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Grapefruit ( Citrus paradisi ), like all citrus fruits, produce very low levels of ethylene throughout development and do not exhibit an ethylene climacteric during ripening ( Aharoni, 1968 ; Eaks, 1970 ). Citrus fruit do exhibit elevated levels

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Abstract

Bearing ‘Valencia’ orange trees growing in a commercial orchard adjacent to a known source of fluoride air pollution were sprayed periodically over a 3-year period with Ca(OH)2 and CaCl2 sprays. These materials in spray and dust forms have been used successfully in the Pacific Northwest to protect gladiolus and peaches from the harmful effects of fluoride-containing atmospheres. It has been postulated that calcium reacts with fluoride gases to produce insoluble and therefore nontoxic CaF2.

Results of these studies indicated that under conditions of high fluoride air pollution, application of lime sprays may improve citrus fruit production, but the mechanism of protection or improvement was not as simple as previously postulated. Immediately adjacent to the source where fluoride air pollution was at a maximum, applications of both Ca(OH)2 and CaCl2 were associated with increased internal fluoride accumulation by ‘Valencia’ orange foliage. With increased distance and therefore diminishing air pollution, an apparent reversal in effect was observed with the calcium sprays resulting in reduced internal accumulation of fluoride.

Although the effects of CaCl2 sprays on fluoride accumulation closely paralleled those obtained with Ca(OH)2, fruit production was not improved where CaCl2 sprays were applied, possibly as a result of induced chloride toxicity.

Open Access

Studies were conducted between November 1999 and April 2003 to evaluate the effectiveness of compounds applied preharvest for reducing postharvest decay on many types of fresh citrus (Citrus spp.) fruit. Commercially mature fruit were harvested two different times after the compounds were applied, degreened when necessary, washed, waxed (without fungicide), and then stored at 50 °F (10.0 °C) with 90% relative humidity. Compared to control (unsprayed) fruit, preharvest application of benomyl or thiophanate-methyl resulted in significantly (P < 0.05) less decay of citrus fruit after storage in nine out of ten experiments, often reducing decay by about half. In one experiment, pyraclostrobin and phosphorous acid also significantly decreased total decay by 29% and 36%, respectively, after storage compared to the control. Only benomyl and thiophanate-methyl significantly reduced stem-end rot (SER; primarily Diplodia natalensis or Phomopsis citri) after storage, with an average of 65% less decay compared to the control. Though benomyl significantly reduced anthracnose (Colletotrichum gloeosporioides) in two of four tests with substantial (>20%) infection and phosphorous acid significantly reduced it once, thiophanate-methyl did not significantly reduce the incidence of anthracnose postharvest. The data suggests that preharvest application of thiophanate-methyl may reduce postharvest SER and total decay similar to preharvest benomyl treatments.

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Fruit of 11 citrus cultivars were evaluated for their response to the experimental abscission material metsulfuron-methyl at 2 mg·L-1 (ppm) active ingredient as an aid to mechanical or hand harvest. Cultivars evaluated included `Ambersweet', `Glen Navel', `Hamlin', and `Valencia' oranges [Citrus sinensis (L.) Osb.], `Robinson' tangerine (Clementine × Orlando, C. reticulata Blanco), `Sunburst' tangerine [`Robinson' × `Osceola', C. reticulata × (C. paradisi Macf. × C. reticulata)], `Murcott' and `Temple' tangor (C. reticulata × C. sinensis), `Orlando' tangelo (C. reticulata × C. paradisi), `Ray Ruby', and `Marsh' grapefruit (C. paradisi). Six of the 11 cultivars were effectively loosened by sprays of metsulfuron-methyl (`Hamlin', `Valencia', `Orlando', `Murcott', `Temple', and `Ray Ruby'). Addition of an adjuvant (Kinetic, 0.125%) was necessary for abscission activity in fruit and leaves. Trees sprayed with metsulfuron-methyl in combination with an adjuvant had higher percent cumulative fruit drop, higher internal ethylene, and lower fruit detachment forces (FDF) than trees sprayed with metsulfuron-methyl alone. `Sunburst' tangerine responded poorly to the abscission material in the presence or absence of Kinetic. Leaf loss was greatest in trees sprayed with metsulfuron-methyl and adjuvant, intermediate in trees sprayed with metsulfuron-methyl alone, and least in control trees. Twig dieback was observed in trees of `Valencia' orange and `Marsh' grapefruit sprayed with metsulfuron-methyl. The peel of some cultivars had irregular coloration and developed pitted areas after harvest. Although metsulfuron-methyl is an effective abscission agent for mature citrus fruit, further work is needed to more accurately define conditions for its safe and dependable use.

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Abstract

The ultrastructure of leaf and fruit surface waxes of citrus developed similarly. The wax layers of immature leaves and fruits were initially amorphous. Small protrusions and isolated regions of upright platelets then developed. All surfaces eventually cracked and uplifted to form large flat irregular plates. Epicuticular wax concentrations (μg/cm2) of new spring flush leaves were initially high, declined rapidly in March-April, and increased to June maxima after which levels declined slightly. Fruit epicuticular wax concentration generally declined in May-June and then increased into November. Secondary alcohols dominated citrus leaf waxes in March-April but quickly decreased or were diluted to trace levels. Overall, the major citrus leaf wax fractions were primary alcohols, with paraffins 2nd in importance. Aldehydes and fatty acids were dominant in citrus fruit waxes. For each cultivar, the relative proportions of individual wax fractions changed during the year. The intracuticular waxes were mainly fatty acids. The relationships between wax ultrastructure and chemistry in developing leaves and fruits are discussed.

Open Access

Abstract

Seal packaging of orange [Citrus sinensis (L.) Osbeck cvs. Valencia and Shamouti], grapefruit (Citrus paradisi Macf. cv. Marsh) and lemons (Citrus limon Burnt, f. cv. Eureka) with high-density polyethylene (HOPE) film (0.01 mm in thickness) delayed softening and inhibited weight loss and deformation of the fruit more than cooling. Sealed fruit at 20°C and 85% relative humidity (RH) had better appearance and were firmer than non-sealed fruit at their lowest temperature possible without chilling injury and 85–90% RH. HOPE seal-packaging also inhibited chilling injury of grapefruit and lemons stored at 5° and 2°C, respectively. The C02 content of grapefruit was unaffected by seal-packaging, hut it was lower at cooler temperatures. Decay of citrus fruit depended more on the storage temperature than on the type of packaging. However, in storage up to 1 month, no significant difference was found in most experiments in decay percentage between orange, grapefruit, and lemon sealed with HOPE and stored in a packing house (13 to 25°C), and non-sealed fruits, at the lowest temperatures possible without chilling injury of 2, 10 and 14°C, respectively.

Open Access

Juice quality of `Valencia' sweet orange [Citrus sinensis (L.) Osb.] trees on Carrizo citrange [C. sinensis × Poncirus trifoliata (L.) Raf.] or rough lemon (C. jambhiri Lush.) rootstocks was determined for fruit harvested by canopy quadrant and separated into size categories to ascertain the direct role of rootstock selection on juice soluble solids concentration (SSC) and soluble solids (SS) production per tree of citrus fruit. SS production per fruit and per tree for each size category was calculated. Juice quality was dependent on rootstock selection and fruit size, but independent of canopy quadrant. Fruit from trees on Carrizo citrange had >20% higher SSCs than fruit from trees on rough lemon, even for fruit of the same size. Large fruit accumulated more SS per fruit than smaller fruit, despite lower juice content and SSC. Within rootstocks, SS content per fruit decreased with decreasing fruit size, even though SSC increased. Rootstock effect on juice quality was a direct rather than an indirect one mediated through differences in fruit size. The conventional interpretation of juice quality data that differences in SSC among treatments, e.g., rootstocks or irrigation levels, or fruit size, are due to “dilution” of SS as a result of differences in fruit size and, hence, juice volume, is only partly supported by these data. Rather, accumulation of SS was greater for fruit from trees on Carrizo citrange than rough lemon by 25% to 30%.

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Randomly amplified polymorphic DNA (RAPD) analysis was used to investigate the histogenic structure of leaf and fruit tissues in four graft chimeras, two intentional chimeras that were produced in combination with `Hamlin' orange [Citrus sinensis (L.) Osbeck] and `Satsuma' mandarin (C. unshiu Marc.), and two naturally occurring periclinal chimera cultivars, Kobayashi Mikan (a graft chimera of C. unshiu and C. natsudaidai Hayata), and Kinkoji Unshu (a graft chimera of C. unshiu and C. obovoidea hort. ex Takahashi). RAPD profiles of the lamina epidermis and the mesophyll cells of specific individuals indicated that the four graft chimeras were interspecific monekto chimeras, whose outermost layer (histogenic layer L-1) of the shoot apical meristem consisted of a species that was different from that in the inner layers (histogenic layers L-2 and L-3). Moreover, juice vesicles, which develop from the inside cells of the pericarp and become the main edible parts of Citrus fruit, were a mixture of the cells from both parental source cultivars. Therefore, the vesicles were at least composed of L-1 and subepidermal inner L-2 cells. This determination of interspecific chimeral construction (which was made possible by molecular techniques) is a valuable finding, in terms of improving Citrus through intentional use of periclinal chimerism.

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