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Ulrich Hartmond, Rongcai Yuan, Jacqueline K. Burns, Angela Grant, and Walter J. Kender

Methyl jasmonate (MJ) was tested as a potential abscission chemical to enhance mechanical harvest of `Hamlin' and `Valenica' orange [Citrus sinensis (L.) Osb.]. In field experiments, a solution of 1, 5, 10, 20, or 100 mm MJ was applied either as a stem wrap to individual fruit or as a spray to entire trees or canopy sectors. Solutions of 10, 20, and 100 mm MJ resulted in significant and consistent reduction of fruit detachment force and caused fruit drop within 7 to 10 days. Fruit loosening was preceded by an increase in the internal ethylene concentration of fruit similar to that of other experimental abscission compounds. While concentrations of 10 mm and less caused no or negligible phytotoxicity, solutions exceeding 10 mm MJ induced unacceptable levels of leaf abscission.

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Diego Barranco, Octavio Arquero, Carlos Navarro, and Hava F. Rapoport

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Lisa Tang, Shweta Chhajed, and Tripti Vashisth

orange ( C. sinensis ), exogenously applied ethylene and its precursor ACC induced abscission of mature fruit ( Malladi and Burns, 2008 ; Merelo et al., 2017 ; Yuan et al., 2005 ). In addition, at the calyx AZ (AZ-C), where mature fruit abscission

Open access

L. Rallo and R. Fernández-Escobar

Abstract

Experiments with heavily-flowering olive trees showed only one period of abscission of flowers and fruit in the 5-6 weeks following full bloom. This abscission of flowers and fruit is responsible for the small percentage of fruit retained to maturity. Most of the fruit drop was concomitant with initial fruit growth for all cultivars. There were no differences in the number of fruit per inflorescence among cultivars, but the percentage of inflorescences with fruit at harvest was related negatively to final fruit size for each cultivar. Thinning of perfect flowers within the inflorescence did not affect fruit set at the inflorescence level; thus, the inflorescence behaved as a unit of fruitfulness. Competition among fruits played a significant role in fruit set. Initial setting induced by pollination and fertilization is counteracted early by fruit abscission originated by competition among fruit. In light of this early abscission, the use of fruit set to indicate response to pollination in previous experiments is questioned.

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Fernando Alferez, Shila Singh, Igor Kostenyuk, and Jacqueline Burns

Abscission is a natural plant process that culminates in the removal of organs from the parent plant. Control of abscission remains an important goal of agriculture, but events that initiate and transduce abscission signals have not been well defined. An understanding of these events may reveal pathways that can be targeted to control abscission. The compound 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) is a pyrazole-derivative that induces abscission selectively in mature citrus (Citrus sinensis) fruit when applied to the canopy. Peel contact is essential for efficacy. Previous work identified CMNP as an uncoupler. Timing of CMNP-induced events in citrus flavedo indicated that increased reactive oxygen species and electrolyte leakage occurred within 30 minutes and 2 hours after application, whereas reduced ATP content was measured 3 hours after application. Phospholipase A2 (PLA2) and lipoxygenase (LOX) activities, and lipid hydroperoxide (LPO) levels increased in flavedo of citrus fruit peel treated with CMNP, indicating that the lipid signaling pathway was activated. A specific inhibitor of PLA2 activity, aristolochic acid (AT), reduced CMNP-induced increases in PLA2 and LOX activities and LPO levels in citrus flavedo and greatly reduced abscission, suggesting that production of phospholipid-derived signals influence abscission process. However, AT treatment failed to halt the reduction in ATP content, indicating that reduction in ATP preceded the increase in PLA2 activity and the biological response. The results demonstrate a link between lipid signaling and abscission in citrus.

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G.W. Stutte and J. Gage

Seed coats of developing fruit of peach [Prunus persica (L.) Batsch cvs. Redkist, Redskin, and Loring] were punctured at 31, 33, and 38 days after full bloom (DAFB), respectively. Injections of water, 390 mg GA3/liter, or 390 mg GA4+7/liter were made immediately following seed puncture. Seed puncture and water injection following puncture resulted in abscission of all fruit. Injection of GA3 and GA4+7 delayed abscission of `Redkist' and `Redskin' fruits of punctured seeds by 6 to 10 days. Both GA treatments resulted in normal growth into Stage II and increased fruit retention through Stage III in `Loring'. About 100 μl of 250, 500, or 1000 mg GA3/liter was injected into the locule of `Loring' fruits following seed puncture at 30, 40, or 50 DAFB. GA treatments at 30 DAFB resulted in≈ 75% fruit set in comparison to seeded control fruit, while fruit treated at 40 and 50 DAFB abscised by the end of Stage II. Increasing GA concentration from 250 to 1000 mg·liter-1 had no additional effect. Movement of the GA was examined by injecting 3H-GA1 into the locule following the puncture treatment. More than 97% remained in the fruit after 96 hours. The percentage of 3H recovered in the seed cavity decreased over time, whereas recovered label increased in both endocarp and mesocarp. The results suggest a potential regulatory role for seed-produced gibberellins during early Stage I of development. We have identified an apparent change in tissue sensitivity to gibberellin induction of seedless fruit development between 30 and 40 DAFB in `Loring' peach.

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Duane W. Greene

A range of concentrations and timings of CPPU application were evaluated in attempt to identify situations in which fruit size, flesh firmness, and soluble solids could be increased while minimizing increased incidence of fruit asymmetry and reductions in flower bud formation and fruit surface red color on 'McIntosh' apples (Malus×domestica Borkh.). The greatest response to CPPU for most attributes evaluated occurred when it was applied at fruit size between 6 mm and 16 mm. The conclusion from this series of experiments is that differential response to CPPU could not be established by altering the time of application. The response to CPPU is linear with increasing concentration. Results suggested that use of 4 to 6 mg·L-1 CPPU on apples to increase fruit size was the maximum and appropriate range to use without causing fruit asymmetry. Chemical name used: N-(2-chloro-4-pyridyl)-N′-phenyl urea (CPPU)

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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.

Open access

D. W. Greene, W. J. Lord, and W. J. Bramlage

Abstract

Applications of (2-chloroethyl)phosphonic acid (ethephon) on ‘McIntosh’ apple trees (Malus domestica Borkh.) in early August at concentrations of 125 to 500 ppm promoted the climacteric rise in respiration, increased soluble solids, fruit abscission, and red color, and also reduced flesh firmness. Results from ethephon applications in July were variable; in 1974 July applications were more effective, and in 1975 less effective, than treatments applied in early August. The effects of ethephon were reduced when 1000 ppm succinic acid-2,2-dimethylhydrazide (daminozide) was combined with the ethephon. No treatment influenced repeat bloom or set the year following application.

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Rongcai Yuan and David H. Carbaugh

between plant growth promoters and inhibitors controls fruit abscission and ripening ( Addicott, 1982 ; Brown, 1997 ; Yuan et al., 2002 , 2003 ). Auxin plays a very important role in the control of fruit abscission ( Osborne, 1989 ). Application of