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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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Tripti Vashisth and Anish Malladi

that in the control treatment (data not shown). The leaf injury treatment did not alter the extent of fruit drop in comparison with the control treatment. Fig. 2. Fruit abscission in response to mechanical wounding in ‘Premier’. Four treatments were

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Hong Zhu, Eric P. Beers, and Rongcai Yuan

and Preston, 1971 ; Yuan and Greene, 2000b ). Shading or removal of spur and shoot leaves, which affects leaf photosynthesis and thereby reduces carbohydrates available to young fruit, causes extensive apple fruit abscission ( Byers, 2003 ; Ferree

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H.F. Rapoport and L. Rallo

The dramatic postanthesis flower and fruit abscission in olive was found to consist of two distinct but overlapping phases for ovaries following the abscission of imperfect flowers. Imperfect flower abscission peaked 8 days after full bloom (FB), while perfect flower and fruit abscission was greatest between 13 to 15 days after FB. Ovary abscission, expressed as percent ovaries abscising per day (relative abscission rate), peaked 15 and 21 days after FB. The first ovary abscission phase includes fertilized and unfertilized ovaries. The second phase occurs once early fruit growth is in progress, suggesting a possible role for substrate competition.

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Jianguo Li, Hong Zhu, and Rongcai Yuan

facilitate seed dispersal ( Addicott, 1982 ). Many apple cultivars such as Red Delicious and Golden Delicious have a serious preharvest fruit abscission problem, which occurs before fruit develop optimum color, maturity, or size ( Schupp and Greene, 2004

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Wei Hai Yang, Chao Zhong Lu, Wei Chen, and Huan Yu Xu

relationship between the carbohydrate availability to the developing fruitlets and their likelihood of abscission. The immature fruit abscission in macadamia was presumably caused by a shortage of available carbohydrates for rapid fruit development ( McFadyen

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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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Jeffrey K. Brecht and Kimberly M. Cordasco

Abscission of cluster tomatoes commonly limits product marketability in the retail environment. Ripening and exogenous ethylene exposure are assumed to play important roles in cluster tomato fruit abscission. `Clarance' and `DRW7229' fruit harvested at either mature green or partially ripened stages did not abscise during storage for 2 weeks at 20 °C and 95% to 100% relative humidity (RH), although respiration and ethylene production indicated that all fruit reached the postclimacteric stage. Exogenous ethylene (1 or 10 ppm) exposure for 8 days at 20 °C and 95% to 100% RH also did not induce fruit abscission for either cultivar, although pedicel and sepal yellowing were observed. Fruit from clusters stored at 20 °C and 20% or 50% RH abscised if sepal shrivel became noticeable before the fruit reached the full red ripeness stage, while no abscission occurred in fruit that reached the full red stage prior to the appearance of sepal shrivel; no fruit stored in 95% to 100% RH abscised. Fruit that ripened prior to the appearance of sepal shrivel were “plugged” (i.e., tissue underlying the stem scar was pulled out) if manual fruit detachment from the pedicel was attempted. These results indicate that there is an interaction of water loss and fruit ripening in promoting abscission zone development in cluster tomatoes.

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Rongcai Yuan and Jianguo Li

applications of NAA delay fruit abscission more than single applications ( Batjer and Moon, 1945 ; Marini et al., 1993 ). However, fruit softening is usually increased by two applications of NAA or warm weather after the first application ( Smock and Gross

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Richard P. Marini, Ross E. Byers, Donald L. Sowers, and Rodney W. Young

Five apple (Malus domestica Borkh.) cultivars were treated with dicamba at concentrations of 0 to 200 mg·liter-1 during 3 years. Although the response varied with cultivar, dose, and year, dicamba always delayed fruit abscission. At similar concentrations, dicamba usually reduced fruit drop more than NAA, but less than fenoprop. Dicamba at 10 mg·liter-1 effectively delayed drop of `Delicious', whereas 20 to 30 mg·liter-1 was required for `Red Yorking', `Rome', `Winesap', and `Stayman'. Dicamba did not influence flesh firmness, soluble solids content, water core, or starch content at harvest or after storage. Chemical names used: naphthaleneacetic acid (NAA); 2-(2,4,5-trichlorophenoxy)propionic acid (fenoprop); 3,6dichloro-2-methoxybenzoic acid (dicamba).