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Open access

William C. Olien and Martin J. Bukovac

Abstract

Five compounds were evaluated for consistent promotion of sour cherry (Prunus cerasus L. cv. Montmorency) fruit abscission under field conditions: (2-chloroethyl)phosphonic acid (ethephon); 2-chloroethyl-tris-(2-methoxyethoxy)-silane (CGA 13586); 2-chloroethyl-methylbis-(phenylmethoxy)-silane (CGA 15281); 1,1,5,5-tetra-methyl-3-dimethylaminodithiobiuret (ER 3952), and beta-hydroxyethylhydrazine (BOH). The compounds were applied to mature trees at equimolar concentrations, and rates of ethylene evolution, effects of temperature on rates of ethylene evolution, and fruit removal forces were measured. Ethephon generated ethylene at adequate rates and was a good promoter of fruit abscission, but its activity was markedly affected by temperature. CGA 15281 promoted fruit abscission with minimal effect of temperature on ethylene evolution. ER 3952 was also a good fruit loosener, although it did not release ethylene directly. CGA 13586 and BOH were not effective in promoting fruit abscission and were poor ethylene generators.

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Duane W. Greene, Aldo J. Crovetti, and Johan Pienaar

of researchers, McLaughlin and Greene (1984) reported that 6-BA had potential as a chemical thinner on apples in since it satisfied the primary characteristics of a chemical thinner: caused fruit abscission, increased fruit size, and promoted return

Open access

B. W. Poovaiah, H. P. Rasmussen, and M. J. Bukovac

Abstract

Dehydrogenase, acid phosphatase, and peroxidase activities were localized histochemically in the lower (pedicel-fruit) abscission zones of sour (Prunus cerasus L.) and sweet (Prunus avium L.) cherry fruits. Highest enzyme activity generally occurred at the juncture of the receptacle and fruit tissues; the region where separation occurred. Both species had a similar peroxidase isozyme pattern; however, 2 bands in sweet cherry had lower intensities than sour cherry. The implications of localized activities of these enzymes in cherry fruit abscission are discussed.

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Luis Rallo

), fruit removal force (FRF), and the FRF/FW ratio, natural fruit abscission before harvesting and homogeneous fruit ripening for the selected seedlings once the fruit have reached their oil content threshold are desirable for cultivar suitability in

Open access

R. E. Holm and W. C. Wilson

Abstract

Two and 3-way combinations of 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release), cycloheximide (Acti-Aid), and chlorothalonil (Sweep) were extensively evaluated for fruit abscission and ethylene production responses on ‘Hamlin’ and ‘Valencia’ oranges (Citrus sinensis (L.) Osbeck). The combinations interact synergistically resulting in far greater fruit loosening than would be expected from additive effects of the individual chemicals. The 3-way combinations of Release plus Acti-Aid plus Sweep consistently gave better fruit abscission than the 2-way combinations of Release plus Acti-Aid and required 25% to 50% less abscission chemical compared to individual abscission chemical usage. Increased fruit abscission activity of the chemical combinations resulted from greater peak fruit ethylene production and higher sustained ethylene levels during the treatment period. Distinct fruit loosening and retightening phases were characterized and shown to be correlated with internal fruit ethylene levels.

Free access

Kiyoshi Banno, George C. Martin, and Robert M. Carlson

Citrate-phosphate buffer induced olive (Olea europaea L.) leaf abscission at pH 3, 5, or 7. Of several sources of P-induced leaf abscission, NaH2PO4 was the most effective. Sensitivity to P was shown by leaf abscission, leaf desiccation, or both among 32 species representing 22 genera. Applied P accumulates in petioles, but its effect on abscission does not seem to depend on ethylene production. The low P content in the ethephon molecule may have an additive effect in ethephon-induced abscission. Stem-fed NaH2PO4 or ethephon resulted in total leaf and fruit abscission. Of the chemicals applied as a foliar treatment, only NaH2PO4 caused fruit abscission with minimal leaf loss. Adding Al2O3 to adsorb P in treatment solutions delayed the abscission effect of ethephon and NaH2PO4. Adding glycerol to NaH2PO4 increased fruit abscission from 50% to ≈80% and leaf abscission from ≈9% to 18%. The presumed effect of glycerol is from slowing the drying rate and thereby increasing P penetration into the fruit abscission zone. The pedicel-fruit cavity is a collection basin for spray accumulation that is not present in the leaf petiole attachment to the stem. This morphological difference probably leads to greater absorption of abscission-inducing materials by fruit. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

Open access

Gregory A. Lang and George C. Martin

Abstract

Fruit-bearing olive (Olea europaea L.) shoots were exposed to more than 100 ethylene (C2H4) treatments to determine if C2H4-induced abscission varied between leaves and fruits in response to manipulation of treatment concentration, duration, and total amount of exogenous C2H4. Nearly three-quarters of the treatments induced greater fruit abscission than leaf abscission on a percentage basis. The potential for optimization of C2H4-induced fruit abscission relative to leaf abscission was examined by calculating the fruit-to-Ieaf (F:L) abscission ratio. Of the treatments inducing at least 75% fruit abscission, the dose range of 150 to 370 μmol C2H4 gave ratios up to 13.3; however, results were highly variable and closely dependent on the interaction of concentration and duration. Response surfaces were created to depict this interaction. Desirable levels of fruit abscission occurred at durations > 30 hr and concentrations > 2 to 3 μl·liter−1. However, excessive leaf abscission occurred at durations of 24 to 48 hr, depending on concentration. Acceptable F:L ratios were found for about 30% of the surface, with the highest ratios occurring for treatments of 3 to 5 μl·liter−1 for 28 to 34 hr.

Open access

R.S. Conrad and F.J. Sundstrom

Abstract

All possible combinations of ethephon at 0, 5000, 10,000, and 15,000 ppm, and calcium as Ca(OH)2 at concentrations of 0, 0.01, 0.1, and 1 m were applied to Tabasco pepper (Capsicum frutescens L.). In the greenhouse, as ethephon rates increased, leaf retention percentages decreased. Over all ethephon rates, as Ca(OH)2 concentration increased, Tabasco leaf retention percentages increased. Ethephon-induced fruit abscission was greatest in less-mature fruit. Overall fruit retention percentages were greatest when ethephon was applied with either 0.1 or 1 m Ca(OH)2. In the field, when ethephon was applied without Ca(OH)2, leaf and fruit abscission was so great that data could not be recorded. When ethephon was applied with 0.1 m Ca(OH)2, percentages of orange and red fruit on the plant increased with an increase in ethephon rate. Chemical name used: (2-choloroethyI)phosphonic acid (ethephon).

Open access

S. A. Weinbaum and T. Muraoka

Abstract

Fruiting branches of French prune (Prunus domestica L.) were exposed to ethylene or the ethylenegenerating (2-chloroethyl)phosphonic acid (ethephon) and subsequently 14C-uptake and ion leakage patterns of excised mesocarp disks were determined. Ion leakage was increased by these treatments, and the magnitudes of variances associated with ethephon-treated samples indicated differences in sensitivity among treated fruit. Under laboratory conditions electrolyte loss was associated with senescence of mesocarp tissue but was not a prerequisite of fruit abscission.

Open access

Max W. Williams

Abstract

The growth retardants 2-chloroethylphosphonic acid (ethephon) and succinic acid-2-2-dimethylhydrazide (SADH) increase flower initiation in young apple trees. At comparable rates, ethephon is more effective than SADH. High rates of ethephon cause flower and fruit abscission. When ethephon was combined with SADH and applied 4 to 5 weeks after bloom, satisfactory promotion of flower bud formation was obtained with lower rates of each chemical with a min of undesirable side effects.