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Open access

G. K. Rasmussen

Abstract

Ethylene production, hydrolytic enzyme activity, and fruit removal force (FRF) were more uniform and consistent when abscission chemicals were applied as dilute as compared to concentrated sprays to ‘Valencia’ orange (Citrus sinensis (L.) Osbeck). Cycloheximide (Acti-Aid), glyoxal-dioxime (Pik-Off), 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release), and Acti-Aid plus chlorothalonil (Sweep) were applied to ‘Valencia’ orange branches, each holding 100 to 120 fruit. The FRF's resulting from commercial concentrate and dilute sprays of Acti-Aid and Acti-Aid plus Sweep were similar to those in the branch tests. Equal amounts of chemical were applied in the dilute and concentrate sprays. Likely, the variation in coverage from concentrate sprays caused ethylene levels to vary greatly in the fruit (0 to 5.7 ppm). In turn, levels of hydrolytic enzyme activity varied as much as 10×, and fruit loosening was inconsistent (0 to 9.7 kg FRF). Release and Acti-Aid plus Sweep were more consistent than Pik-Off and Acti-Aid in dilute spray applications.

Open access

T. Adair Wheaton, W. C. Wilson, and R. E. Holm

Abstract

Mature Florida ‘Valencia’ oranges [Citrus sinensis (L.) Osbeck] go through a period of reduced response to abscission chemicals. This nonresponsive period is characterized by both a reduction in the amount of ethylene induced by abscission chemicals and by decreased sensitivity of the abscission process to exogenous ethylene. During the nonresponsive period, application of the abscission chemical 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release) induced less ethylene formation and less reduction in fruit removal force than at times either prior to, or following, the nonresponsive period. Experiments with radioactive Release showed that uptake was not a factor in the reduced effectiveness of this material during the nonresponsive period. Abscission of explants induced by exogenous ethylene was slower during the nonresponsive period. Mature ‘Valencias’ also go through a period of regreening. Regreening and the nonresponsive period may begin at about the same time, but regreening continues after the nonresponsive period is over. In addition, color changes induced by exogenous ethylene remain similar throughout the regreening and nonresponsive periods, but abscission of explants induced by exogenous ethylene is reduced only during the nonresponsive period. These differences in time-course and ethylene sensitivity between regreening and the nonresponsive period allow differentiation of these two processes.

Free access

Jacqueline K. Burns, Louise Ferguson, Kitren Glozer, William H. Krueger, and Richard C. Rosecrance

mg·L −1 dikegulac (Atrimmec; PBI/Gordon Corp, Kansas City, MO); or 1000 or 2000 mg·L −1 5-chloro-3-methyl-4-nitro-1 H -pyrazole (CMNP; previously formulated by Abbott Laboratories, Libertyville, IL). Maximum, minimum, and average temperatures on the

Full access

Jacqueline K. Burns, Richard S. Buker III, and Fritz M. Roka

An abscission agent [5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP)] was applied to `Hamlin' and `Valencia' orange (Citrus sinensis) trees at concentrations ranging from 0 to 500 ppm in a volume of 300 gal/acre. Four days after application, fruit were mechanically harvested with either a trunk shake-and-catch or a continuous canopy shake-and-catch system commercially used in Florida. Harvesting conditions were varied by limiting the actual trunk shake time of the trunk shaker to 2, 4, or 7 seconds, or by altering the ground speed of the canopy shaker (1.0, 1.5, or 2.0 mph). In general, increasing duration of shake and the application of CMNP increased percent mature fruit removal and decreased the amount of fruit remaining in the tree. Increasing CMNP concentration decreased fruit detachment force but increased post-spray fruit drop. Comparison of short duration shake times in CMNP-applied trees with trees harvested at longer durations either sprayed or not sprayed with CMNP indicated no significant difference in percent mature fruit removal. The results demonstrate that CMNP application increases harvesting capacity of trunk and canopy shakers by reducing time necessary to harvest each tree while maintaining high percent mature fruit removal.

Free access

Jacqueline K. Burns, Fritz M. Roka, Kuo-Tan Li, Luis Pozo, and Richard S. Buker

An abscission agent (5-chloro-3-methyl-4-nitro-1H-pyrazole [CMNP]) at 300 mg·L–1 in a volume of 2810 L·ha–1 was applied to Valencia orange trees [Citrus sinensis (L.) Osb.] on 22 May 2004. At this time, immature and mature fruit were present on the tree simultaneously. Three days after application, fruit were mechanically harvested using a trunk-shake-and-catch system. The power to the shaker head was operated at full- or half-throttle (FT or HT, respectively), and the duration of trunk shaking was 2 seconds at FT or 4 seconds at FT and HT. Mature fruit removal percentage and number of immature fruit removed, and fruitlet weight and diameter were determined. Mature fruit removal percentage with 2 seconds at FT or 4 seconds at FT harvesting ±CMNP, or 4 seconds at HT + CMNP was not significantly different and ranged between 89% to 97%. Harvesting at 4 seconds HT without CMNP removed significantly less mature fruit than any treatment. CMNP did not affect immature fruit removal by the trunk shaker. Harvesting at 4 seconds at HT removed significantly less immature fruit than 2 seconds at FT or 4 seconds at FT. No significant difference in fruitlet weight or diameter was measured between any trunk shaker harvest operation and CMNP treatment. Trunk shaking frequency was estimated to be 4.8 and 8.0 Hz at HT and FT, respectively. Yield in 2005 was determined on the same trees used for harvest treatments in 2004. CMNP did not impact yield. No significant difference in yield was seen between the hand-picked control and 4 seconds at HT, whereas yield in the remaining treatments was lower. The results demonstrate that CMNP application combined with low frequency trunk shaker harvesting can achieve high percentage of mature fruit removal with no significant impact on return yield of the following crop.

Free access

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.

Open access

F. S. Davies, W. C. Cooper, and R. E. Holm

Abstract

Four abscission materials were evaluated to determine their effects on ethylene production and abscission of fruit and leaves of orange (Citrus sinensis (L.) Osbeck cvs. Hamlin and Valencia): 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release) glyoxal dioxime (Pik-Off), cycloheximide (3-[2-(3,5-dimethyl-2-oxocyclohexyl-2-hydroxyethyl]-glutarimide or Acti-Aid) and cycloheximide in combination with chlorothalonil (DS-27914). All chemicals enhanced internal fruit ethylene levels and subsequent fruit loosening. However, the magnitude and timing of the fruit ethylene response varied with each chemical and correlated with fruit loosening and subsequent retightening. The pattern of ethylene production may indicate the optimum fruit harvest period and the degree of leaf abscission for each chemical.

Open access

Kathleen B. Evensen, Michael G. Bausher, and R. Hilton Biggs

Abstract

Ethylene production in peel explants of ‘Valencia’ oranges [Citrus sinensis (L.) Osbeck] treated with 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release) was similar in pattern to ethylene production by whole fruits treated with the chemical. Smaller amounts of ethylene were produced by untreated peel explants. Explants from fruit harvested in October and March showed similar patterns of ethylene evolution when untreated and when Release was applied. The response to this chemical was localized in the flavedo. Ethylene production was dependent on temperature in both untreated and Release-treated peel explants, but the ethylene response to the chemical was particularly temperature-dependent. The temperature optimum in both cases was approximately 25°C. Peel disks from regreening fruit generally produced less ethylene than disks from nongreening fruit when Release or glyoxal dioxime (ethanedial dioxime, Pik-Off) was applied. The magnitude of the difference between regreening and nonregreening disks depended on the concentrations of Pik-Off or Release applied.

Free access

U. Hartmond, J.D. Whitney, J.K. Burns, and W.J. Kender

Two field studies were conducted to evaluate the effect of metsulfuron-methyl and 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMN-pyrazole) on abscission of `Valencia' orange [Citrus sinensis (L.) Osbeck] during the 3-month harvest season. Solutions of metsulfuron-methyl at 0.5, 1, and 2 mg·L-1 active ingredient (a.i.) were applied at 10-day intervals beginning on 13 Feb. and ending 18 May 1998. Early in the harvest season, 1 or 2 mg·L-1 metsulfuron-methyl significantly reduced fruit detachment force (FDF) 14 days after application. Metsulfuron-methyl was less effective during a 4- to 6-week period following bloom (“less-responsive period”). After this period, metsulfuron-methyl regained the ability to loosen fruit. Applications of 2 mg·L-1 a.i. were more effective than 1 mg·L-1 in reducing FDF and causing leaf drop, but 0.5 mg·L-1 a.i. had little or no effect on FDF. Flowers and leaflets on developing shoots and young fruit completely abscised with 1 and 2 mg·L-1 a.i. Defoliation and twig dieback was extensive at all concentrations and spray dates, eliminating metsulfuron-methyl as a commercially viable abscission agent for citrus. In a separate experiment CMN-pyrazole at 50 and 100 mg·L-1 a.i. and metsulfuronmethyl at 0.5 mg·L-1 a.i. were applied to `Valencia' trees to determine fruit removal with a trunk shake and catch harvesting system. Application of both abscission materials before and after the “less-responsive period” resulted in a 10% to 12% increase in fruit removal when compared to control trees. Less than a 35% reduction in FDF was sufficient to significantly increase fruit removal. Only 100 mg·L-1 a.i. CMN-pyrazole significantly increased fruit removal when applied during the “less-responsive period.” Chemical names used: Methyl-2-(((((4-Methoxy-6-Methyl-1,3,5-Triazin-2-yl)-Amino)Carbonyl) Amino)Sulfonyl)Benzene (Metsulfuron-methyl); 5-Chloro-3-methyl-4-nitro-1-H-pyrazole (CMN-pyrazole).

Free access

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.