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George C. Martin, Chic Nishijima, and Jack D. Early Jr.

Olive fruit persistence is a crucial component of yield and an important factor in estimating alternate bearing potential.

Unfortunately, measurement of fruit persistence exhibit considerable variation, with coefficients of variation greater than 100. Such a high degree of variation makes field studies on questions regarding flowering and fruiting unmanageable due to the large number of experimental units necessary. To determine the source of this variation and how it might be reduced, comparisons of flower and fruit number per node were made within branches and trees over the course of two seasons. Results show that while the largest population of flowers are most distal on the branch, the central portion of the branch contains the majority of the final fruit population and has the lowest coefficient of variation. Furthermore, variation in the number of flowers and fruits is greater between branches than between nodes or trees. The implications of these data on experimental design are discussed and a design is proposed for reducing variation and labor needs.

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Luis Pozo, Rongcai Yuan, Igor Kostenyuk, Fernando Alférez, Guang Yan Zhong, and Jacqueline K. Burns

1-MCP is a gaseous ethylene binding inhibitor that controls or delays ethylene-related postharvest problems in a range of horticultural commodities. Our previous work demonstrated that exposure of calamondin to 1-MCP 16 hours before canopy sprays of ethephon greatly reduced unwanted leaf drop while only partially inhibiting the ability of ethephon to cause fruit loosening. The objective of this work was to determine whether formulated 1-MCP (SmartFresh) could be used in the field to stop defoliation caused by abscission agent applications without significantly altering abscission agent-induced fruit loosening. Spray solutions containing 400 mg·L-1 ethephon with 0, 1, 2.5, and 5 mm 1-MCP were applied to canopies of `Hamlin' and `Valencia' (Citrus sinensis). Timing of 1-MCP applications was a) 24 hours before, b) in combination with, or c) 24 hours after ethephon. Ethephon at 400 mg·L-1 significantly reduced fruit detachment force (FDF) but caused >70% leaf drop within 15 days after application in both cultivars. Applications of 1-MCP reduced ethephon-associated leaf abscission but had little effect on the ability of ethephon to reduce FDF. Timing of 1-MCP applications did not affect the ability of ethephon to cause fruit loosening; however, the best consistent treatment for control of leaf drop was achieved with the combined application of 5 mm 1-MCP and 400 mg·L-1 ethephon. 1-MCP was used in combination with the abscission agents coronatine, methyl jasmonate (MeJa) and 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) to determine its effect on leaf drop and fruit loosening. Leaf drop in trees treated with ethephon, coronatine, and MeJa was reduced by addition of 1-MCP. However, fruit loosening was largely prevented when 1-MCP was used in combination with coronatine or MeJa. Like ethephon, CMNP-induced fruit loosening was not affected by 1-MCP. The results demonstrate the ability to control ethephon-induced leaf abscission without affecting mature fruit loosening by targeting ethylene binding in citrus.

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Duane W. Greene, Alan N. Lakso, Terence L. Robinson, and Phillip Schwallier

Attempts have been made to identify factors that can be easily quantified and serve as early harbingers of ultimate fruit abscission. Ward and Marini (1999) applied a high rate of ethephon plus carbaryl to ‘Golden Delicious’ and ‘Delicious’ apples

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Duane W. Greene

AVG was applied as the ReTain formulation over three harvest seasons to determine the influence of time of application on drop control efficacy and its influence on fruit maturity of 'McIntosh' apples. Effective drop control was achieved through the commercial harvest season with application of AVG made from 1 to 6 weeks before the anticipated start of harvest for untreated fruit. Drop control extended beyond the normal harvest period when application was made either 2 weeks or 1 week before anticipated harvest. Application made between 6 and 4 weeks before anticipated harvest generally delayed parameters associated with ripening, such as softening, degradation of starch, and development of red color, more than applications made on later dates. While AVG consistently and effectively retarded abscission, the length of time it controlled drop varied from year to year, even when used on similar trees in the same block. Once applied, it required 10 to 14 days before AVG started to retard fruit abscission. AVG controlled drop linearly with increasing concentration. AVG was a superior drop control compound than NAA. Chemical names used: aminoethoxyvinylglycine (AVG), naphthaleneacetic acid (NAA).

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Steven J. McArtney

Ethylene evolution from detached fruiting apple spurs was measured after application of various bloom and post-bloom thinning agents. Ethylene evolution from fresh detached spurs of `Splendor' apple trees increased one day after application of a bloom thinning spray of ethephon or NAA, and remained higher than rates of ethylene evolution by detached spurs from unsprayed control trees for 6 (NAA) or 10 (ethephon) days. Both ethylene evolution and fruit abscission during the initial drop period were higher on trees treated with ethephon compared to NAA, however final fruit set was similar for these two treatments. Ethylene evolution was significantly higher following NAA application onto `Fuji' trees compared with NAAm, but final fruit set was reduced by a similar amount (≈20%) for both of these materials. Application of BA to `Pacific Rose™' apple trees when the average diameter of spur fruit was either 4 mm (6 days after full bloom) or 7 mm (12 days after full bloom) resulted in a significant increase in the rate of ethylene evolution and also reduced final fruit set. When application of BA was delayed until the average diameter of spur fruit was 14 mm (24 days after full bloom) neither the rate of ethylene evolution or final fruit set was affected. Although an increase in the rate of ethylene evolution was a prerequisite for thinning in the present experiments, the magnitude of this increase was not related to the final thinning efficacy. Chemical names used: benzyladenine (BA); 2-chloroethyl phosphonic acid (ethephon); naphthaleneacetic acid (NAA); naphthalene acetamide (NAAm).

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Steven J. McArtney and John D. Obermiller

Chemical stimulation of young fruit abscission during the first 3 weeks after bloom is a key management consideration in modern apple ( Malus ×domestica Borkh.) production systems. Sequential applications of chemical thinners with different modes

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Steven J. McArtney, Suzanne R. Abrams, Derek D. Woolard, and Peter D. Petracek

that a transient limitation in carbohydrate supply can act as a strong trigger for abscission of apple fruit. Exogenously applied ABA during early fruit development stimulates fruit abscission in apples ( Edgerton, 1971 ; Greene et al., 2011

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Duane W. Greene

fewer thinners that are available for use on or are effective on pears than on apples. Recently there has been increased interest in understanding the way(s) chemical thinners cause fruit abscission ( Greene, 2010 ). It is reasoned that greater

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James R. Schupp, Thomas M. Kon, and H. Edwin Winzeler

carboxylic acid on the rate of ethylene release from detached fruiting spurs and on fruit abscission in apple J. Hort. Sci. Biotechnol. 86 640 644

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Duane W. Greene, James R. Schupp, and H. Edwin Winzeler

, and the combination of ABA plus BA resulted in significant thinning when expressed either as fruit per centimeter LCSA or as percent set ( Table 1 ). The interaction between ABA and BA for fruit abscission was significant. ABA, BA, and the combination