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William C. Kazokas and Jacqueline K. Burns

Mature and immature `Valencia' orange [Citrus sinensis (L.) Osbeck] and immature `Valencia' orange and `Tahiti' lime (Citrus latifolia Tan.) fruit with attached pedicels were treated with 8 μL·L-1 ethylene for periods up to 24 hours. Endo-β-1,4-glucanase (cellulase) activity and gene expression were determined in fruit abscission zones during and after ethylene exposure. Cellulase activities were not detected in mature `Valencia' orange and immature `Tahiti' lime fruit abscission zones immediately following harvest and after 6 hours of ethylene treatment. After 12 hours of ethylene treatment, cellulase activity increased and was highest after 24 hours. Cellulase gene expression preceded the rise in cellulase activity and was detectable after 6 hours of ethylene treatment, but then declined after 12 hours. Following transfer to air storage, abscission zone cellulase activity in mature `Valencia' fruit remained high, whereas activity in immature `Tahiti' fruit declined. After 168 hours air storage, activity in abscission zones of mature `Valencia' fruit decreased slightly, but activity in abscission zones of immature `Tahiti' lime fruit increased to the highest level. Expression of abscission zone cellulase gene Cel-a1 in abscission zones of mature `Valencia' fruit markedly increased after transfer to air and was highest after 48 hours air storage. Cel-a1 expression returned to low levels after 168 hours of air storage, but expression of cellulase gene Cel-b1 remained at low levels throughout the air storage period. Expression of Cel-a1 and Cel-b1 declined in fruit abscission zones of immature `Valencia' and `Tahiti' lime fruit upon transfer to air. After 168 hours of air storage, expression of Cel-a1 again rose to high levels but Cel-b1 remained low. The results suggest that differences in cellulase activity and gene expression measured in mature and immature fruit abscission zones during ethylene treatment and subsequent air storage may, in part, explain the differential response of mature and immature fruit to abscission agents.

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Rongcai Yuan, Walter J. Kender, and Jacqueline K. Burns

The effects of removal of young fruit and application of auxin transport inhibitors on endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) concentrations were examined in relation to the response of mature `Valencia' orange [Citrus sinensis (L.) Osb.] fruit to abscission materials. ABA concentrations were increased in the fruit abscission zone and pulp but not in the pedicel, peel, or seed of mature fruit by removal of young fruit during the period of reduced response of mature fruit to abscission materials in early May. However, removal of young fruit slightly decreased IAA concentrations in leaves and the abscission zone and pedicel of mature fruit but had no effect on the IAA concentrations in the peel, pulp, or seed of mature fruit. Young fruit had higher IAA concentrations in the abscission zone and pedicel than mature fruit. Application of 2,3,5-triiodobenzoic acid (TIBA), an IAA transport inhibitor, reduced IAA concentrations in the abscission zone of mature fruit but did not influence the IAA concentrations in the pedicel and peel when applied directly to an absorbent collar tied around the pedicel 2 cm above the fruit abscission zone during the less responsive period in early May. ABA concentrations were increased drastically in the fruit abscission zone and pedicel but not in peel by TIBA application. Applications of ABA, or IAA transport inhibitors such as naringenin, quercetin, or TIBA comparably increased the response of mature fruit to the abscission material 5-chloro-3-methyl-4-nitro-1 H-pyrazole (CMN-pyrazole) in early May. These data suggest that young fruit reduce the response of mature `Valencia' oranges to abscission materials through increasing IAA concentrations and decreasing ABA concentrations in the abscission zone of mature `Valencia' orangees.

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Tripti Vashisth and Anish Malladi

( Austin and Williamson, 1977 ; Howell et al., 1976 ; Mainland et al., 1975 ; Takeda et al., 2008 ). Fruit detachment may occur either through the physiological process of abscission or through tearing and physical separation of the fruit from the parent

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Matthew W. Fidelibus, Kimberley A. Cathline, and Jacqueline K. Burns

grape berries are desired by the food service industry for use in salads, and better quality wine may be made from fruits with less mechanical damage after machine harvest ( Meyer, 1969 ). Despite the potential advantages provided by an abscission

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Andrea E. Fiebig, J.T.A. Proctor, D.P. Murr, and R.D. Reeleder

Field experiments over 2 years were used to determine the effect of ethephon on: plant growth, weight of berries, proportion of red, green and immature berries, and root weight (economic yield) of 3-year-old north american ginseng plants (Panax quinquefolius L.). Ethephon sprays applied during bloom that thoroughly wetted the foliage and inflorescences immediately induced crop canopy descent (epinasty) exposing inflorescences and subsequently reducing plant height. Within a week the desired inflorescence and peduncle browning and flower drop took place. In each of four experiments ethephon, over the range 500 to 4000 mg·L-1, reduced berry weight and percent red berries, and increased the percent immature berries linearly. However, the responses to ethephon were variable. The highest concentration of 4000 mg·L-1 ethephon caused similar results in both years to the traditional practice of hand removal of inflorescences, but foliar reddening and some defoliation were observed. Buffering ethephon sprays at pH 2.6, 4.0, 5.0, and 6.0 gave similar results. The surfactant Tween 20 did not increase the effectiveness of the sprays. Generally, multiple applications of ethephon at lower concentrations were no more effective than comparable single higher concentration sprays. Carry-over effect of ethephon in the second year included crop stunting, an increase in root weight, and berry weights and berry color proportions similar to those plants on which hand removal was carried out in the first year. Chemical names used: 2-chloroethyl phosphonic acid (ethephon).

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Lauren C. Garner and Carol J. Lovatt

increased flower and fruit abscission can occur as a result of numerous factors, including temperature extremes, nutritional deficiencies, and genetic factors. Even with optimal conditions, avocado flower and fruit abscission is still excessive. Avocado

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Polyxeni M. Filios and William B. Miller

exogenous or endogenous in nature. In many floriculture crops, ethylene results in flower, bud, or leaf abscission, epinasty, and hastening of senescence ( Gibson et al., 2000 ; Reid and Jiang, 2012 ). Skog et al. (2001) measured ethylene levels in midsize

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Naveen Kumar and Robert C. Ebel

Abscission is an active process by which plants shed vegetative and reproductive parts during various developmental stages of their life cycle though a narrow zone of anatomically distinct cells that constitute AZ ( Estornell et al., 2013 ). Besides

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Tripti Vashisth and Anish Malladi

Abscission is a physiological process involving the detachment of an organ from the plant at specific regions termed abscission zones (AZs; Roberts et al., 2002 ). Organ detachment through abscission may be the result of an intricately controlled

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Luis Pozo and Jacqueline K. Burns

The use of the abscission agent 5-chloro-3-methyl-4-nitro-1 H -pyrazole (CMNP) in combination with mechanical harvesting increases mature sweet orange fruit removal without causing phytotoxicity to leaves and young developing fruit through most of