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Galen K. Brown

Hand picking, by snapping each fruit from its stem, has been the traditional method of harvesting Florida oranges (Citrus sinensis) and grapefruit (C. paradisi) for processing. A harvest mechanization program was active from about 1960 to 1985, but mechanical methods were not adopted. In July 1994, a new harvesting research and development program was initiated by the Florida Department of Citrus. The growers are taxed about $0.01/field box of production to fund the program. An industry Advisory Council oversees the program, and recommends projects and funding. The new program has provided training videos to improve hand harvest management/productivity, developed several methods for mechanical harvesting, and discovered/evaluated several fruit abscission agents. Mechanical harvesting use is increasing, and about 6880 of the 237,498 ha (17,000 of the 586,859 acres) of oranges were mechanically harvested during the 2002-03 season. Two mechanical systems can increase labor productivity by 5 to 15 times and reduce unit harvesting cost by 50% or more. Such savings are essential for effective competition in free-trade markets and for operation with resident labor. Many old-style plantings will need to be replaced over the next 10 years. The harvesting program accomplishments are discussed.

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Larry R. Parsons, T. Adair Wheaton, Nick D. Faryna, and John L. Jackson

The severe advective freeze of 23-26 Dec. 1989 killed most nonprotected trees in Florida's northern citrus region. Minimum temperatures reached - 8.3C with >43 hours below freezing. Microsprinklers elevated to a height of 0.6 or 0.9 m and placed inside the canopy of young `Hamlin' and navel orange trees [Citrus sinensis (L.) Osb.] provided excellent protection to heights well above 1 m. Initial survival height of trees with emitters elevated to 0.9 m was higher than has been reported for microsprinklers at a conventional 0.2-m height in earlier severe freezes. Trees rapidly approached prefreeze canopy size from regrowth of the protected scaffold branches. Six months after the freeze, trees protected by microsprinklers elevated to 0.6 m and delivering 26 or 47 liters·hour-1 had regrown to a height of 1.4 or 1.7 m, respectively. Trees with microsprinklers at a height of 0.9 m and delivering 101 liters·hour -1 had regrown to a height of 2.5 m. Trees with no microsprinkler irrigation were killed to the ground. Twelve months after the freeze, trees with elevated microsprinklers were still significantly taller and showed greater recovery than those with microsprinklers near the ground.

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Victor Rodov, Shimshon Ben-Yehoshua, Jong Jin Kim, Boris Shapiro, and Yitzhak Ittah

Ultraviolet (UV) illumination (254 nm) induced production of the phytoalexin scoparone in flavedo of kumquat (Fortunella margarita Lour. Swingle cv. Nagami) and orange [Citrus sinensis (L.) Osbeck cvs. Shamouti and Valencia]. Trace amounts of scoparone (<2.0 μg·g-1 fresh weight of flavedo) were detected in nontreated fruits. Phytoalexin accumulation in kumquat reached a peak of 530 μg·g-1 11 days after illumination, hut the amount declined rapidly, returning to a trace level 1 month after treatment.. Production of scoparone in illuminated fruits was enhanced by increasing the UV dose from 1.5 × 103 to 9.0 × 103 J·m-2 for orange and from 0.2 × 103 to 1.5 × 103 J·m-2 for kumquat and by raising the storage temperature from 2 to 17C. Phytoalexin accumulation correlated with an increase in antifungal activity of flavedo extracts. UV-illuminated kumquat fruit inoculated with Penicillium digitatum Sacc. 2 days after treatment had a lower incidence of decay than the control. Illumination of previously inoculated fruit failed to prevent decay. Kumquat fruit stored at 17C showed signs of UV-induced peel damage. Chemical name used: 6,7-dimethoxycoumarin (scoparone).

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Rongcai Yuan, Fernando Alferez, Igor Kostenyuk, Shila Singh, James P. Syvertsen, and Jacqueline K. Burns

The effects of 2 consecutive years of annual defoliation during the harvest season on fruit size, yield, juice quality, leaf size and number were examined in trees of the midseason cultivar `Hamlin' and the late-season cultivar `Valencia' orange [Citrus sinensis (L.) Osb.]. In `Hamlin', removal of up to 50% of the leaves in late November had no effect on fruit yield, fruit number, fruit size, soluble solids yield, juice °Brix, and °Brix to acid ratio of juice the following year. In `Valencia', removal of 50% of the leaves in late March decreased fruit yield and soluble solids yield but did not affect Brix or the Brix to acid ratio of the juice. Leaf size of new flush was reduced by removal of 50% of the leaves in both cultivars but there was little effect on total canopy size. There were no measured effects of removing 25% of leaves from tree canopies. Thus, canopy growth, fruit yield, fruit quality, and leaf size were not negatively impacted when annual defoliations did not exceed 25% of the total canopy leaf area in `Valencia' and `Hamlin' orange trees for two consecutive years. Overall, fruit weight increased linearly with increasing ratio of leaf area to fruit number, suggesting that fruit enlargement can be limited by leaf area.

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Thomas A. Obreza and Robert E. Rouse

The growth response of young `Hamlin' orange (Citrus sinensis L. Osbeck) on Carrizo citrange (C. sinensis × Poncirus trifoliatu L. Raf.) trees to N-P-K fertilizer rates under field conditions in southwestern Florida was studied to determine the minimum fertilizer required to bring trees into maximum early production. The highest 8N-1.8P-6.6K fertilizer rate was 2.72,5.45, and 8.17 kg/tree in 1989,1990, and 1991, respectively. Additional fertilizer treatments equaled 50%, 25%, or 13% of the maximum rate. Fertilizer sources contained either all water-soluble N (applied more frequently) or 40% to 50% controlled-release N (applied less frequently), and they did not affect fruit yield or quality. The response of trunk cross-sectional area, tree canopy volume, and fruit yield to fertilizer rate was described by a linear plateau model. The model predicted a fruit yield of 22.6 kg/tree at the estimated critical fertilizer rate of 48% of maximum. Fruit yield at the 50% maximum rate averaged 21.2 kg/tree. As fertilizer rate increased, total soluble solids concentration (TSS) in juice and the TSS: acid ratio decreased, but weight per fruit and TSS per tree increased. A fruit yield >21 kg/31-month-old tree indicated vigorous growth.

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Kenneth Marsh, Pedro Gonzalez, and Ed Echeverría

Tonoplast vesicles isolated from juice cells of mature `Valencia' oranges [Citrus sinensis (L.) Osbeck] showed similar tonoplast-bound vacuolar ATPase (V-ATPase) and inorganic pyrophosphatase (V-PPiase) activity as measured by product formation. Both proton pumps were able to generate a similar pH gradient, although steady-state was reached faster with ATP as substrate. When a ΔpH of 3 units was imposed (vesicle lumen pH of 4.5 and incubation medium of 7.5), tonoplast-bound PPiase was not able to significantly amplify the existing ΔpH. Although not able to function as a H+ pump, V-PPiase effectively synthesized PPi in the presence of inorganic phosphate (Pi). Formation of PPi by V-PPiase was enhanced by ATP but inhibited by NaF, gramicidin, and by antibodies raised against V-PPiase from mung bean [Vigna radiata (L.) R. Wilcz. (Syn. Phaseolus aureus Roxb.)]. Immunological analysis demonstrated an increase in V-PPiase protein with fruit maturity. Data indicate that under in vivo conditions, the V-PPiase of mature orange juice cells acts as a source of inorganic pyrophosphate (PPi) but not as a H+ pump. We propose that synthesis of PPi provides a mechanism for recovery of stored energy in the form of the pH gradient across the vacuole during later stages of development and postharvest storage.

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Anwar G. Ali and Carol J. Lovatt

The ability of arginine (50 mM), putrescine (10 and 20 mM), and spermidine (10 and 20 mM) to enhance low temperature stressed-induced flowering of 5-year-old container-grown `Washington' navel orange trees was evaluated. The metabolites were applied to the foliage at the end of the 4-week low-temperature treatment of 8-h days at 10°C and 16-h nights at 7°C; the trees were then moved to warmer conditions.

All treatments had a positive effect on floral intensity. Putrescine (20 mM) and spermidine (10 mM) significantly increased (P = 0.05) total flower number and both the number and proportion of leafless inflorescences per tree. However, the number of floral shoots per tree, as well as the number of leafy inflorescences and number of vegetative shoots were not significantly influenced by the metabolites.

The results suggest that polyamines are important to the development of flowers, but not leaves, along the axis of the inflorescence.

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Frederick S. Davies and Glenn Zalman

Our objectives were to determine if gibberellic acid (GA3) application at color break in the fall affected the juice content, soluble solids content (SSC), titratable acid (TA), and ratio of SSC: TA of `Hamlin' orange (Citrus sinensis) fruit following moderate to severe freezes. We also wanted to know if GA3 affected the post-freeze rate of decrease in juice content, fruit and tree cold hardiness, and the amount of fruit drop following a freeze. GA3 (18 floz/acre) was applied at color break in the fall of 2002, 2003, and 2004 to `Hamlin' orange trees on Swingle citrumelo (C. sinensis × Poncirus trifoliata) rootstock planted in 1995 at Gainesville, Fla. Moderate to severe freezes occurred in all three seasons. Fruit were harvested at about 2-week intervals following freezes in each season and the internal fruit quality was determined. GA3-treated fruit generally had higher juice content compared with nontreated fruit for 8 weeks after moderate to severe freezes in all three seasons, which may be economically important to citrus processors and growers since Florida growers are paid based on fruit pounds-solids (juice content × SSC). The rate of decrease in juice content over time was similar for both treatments in seasons one and two, but was less for GA3-treated fruit than nontreated fruit in season three. In addition, SSC was equal to or slightly greater for fruit treated with GA3 than for nontreated fruit. Fruit drop rate and magnitude were also significantly less for the GA-treated compared with nontreated trees in two of three seasons. GA3 did not affect fruit, leaf, or tree cold hardiness in any season.

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Krista C. Shellie and Robert L. Mangan

`Valencia' oranges [Citrus sinensis (L.) Osbeck] were exposed to moist, forced air (MFA) at 46, 47, or 50C for 1, 2, 3, or 4 hours to identify the maximum temperature and duration of exposure for which there was no detectable reduction in fruit quality. The flavor of oranges exposed to MFA at 47 or 50C was rated significantly inferior to that of oranges exposed to 46C. The degree minutes that accumulated in the center of the fruit between 2 and 4 hours and the maximum fruit center temperature during the heat treatment were associated with inferior fruit flavor. Oranges exposed to MFA at 46C for up to 4 hours could not be distinguished from the nonheated fruit. MFA at 46C is a promising quarantine treatment for `Valencia' oranges.

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Raphael Goren, Moshe Huberman, and George C. Martin

Previous studies have demonstrated that phosphorus, which stimulates ethylene biosynthesis, induces abscission of olive leaves directly without the involvement of ethylene. In the present study this possibility was further explored by comparing the effects of an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), and an ethylene action inhibitor, 2,5-norbornadiene (NBD), in olive [Olea europaea (L.) `Manzanillo'] and citrus [Citrus sinensis (L.) Osbeck `Shamouti']. In olive, leaf abscission was always induced in the presence of KH2PO4 with or without AVG and NBD (alone or in combination), but it was much more pronounced when KH2PO4 was applied alone. In citrus, KH2PO4 did not induce leaf abscission in the presence of NBD during the first 48 (detached shoots) or 60 hours (leaf explants) despite the high levels of ethylene production by the tissues. Our results demonstrate that phosphorus can, at least partly, act independently of ethylene action in inducing leaf abscission in olive but not in citrus.