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Mohamed El-Otmani, Charles W. Coggins Jr., and Andrew Duymovic

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Mohamed El-Otmani and Charles W. Coggins Jr.

Abstract

Changes in ‘Washington’ navel orange [Citrus sinensis (L.). Osbeck] fruit epicuticular wax quantity and structure were followed during fruit development, maturation, and senescence. Whole-tree sprays of 10 ppm GA3, 16 ppm 2,4-D, and a combination of GA3 (10 ppm) plus 2,4-D (16 ppm) were made at fruit color-break, and effects on wax were examined at 4-week intervals. The total epicuticular wax produced per fruit and per unit of fruit surface area increased with time on control and on treated fruit. GA3-treated fruit produced significantly lower amounts of wax per unit of surface area than did control or fruit treated with 2,4-D alone. Total epicuticular wax per unit of fruit surface area of the control was similar to that of the 2,4-D-treated fruit until late in the season, when that of the control significantly exceeded that of the 2,4-D treatment. Wax per unit of fruit area of the GA3-treated fruit was not significantly different from that of the GA3 plus 2,4-D-treated fruit until late in the season, when GA3 plus 2,4-D treatment resulted in significantly higher values. Scanning electron microscopy revealed significant changes in surface morphology and ultrastructure of the epicuticular wax during fruit development, maturation, and senescence. Control fruit and 2,4-D-treated fruit were similar, but GA3 delayed ultrastructural changes that were seen in the control fruit. The incidence of ‘sticky’ rinds was reduced significantly by GA3 treatment, and ‘sticky’ rind surface wax had a structure similar to that of senescing surfaces. Chemical names used: (2,4-dichlorophenoxy)acetic acid (2,4-D); gibberellic acid (GA3).

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Elisabetta Nicolosi, Stefano La Malfa, Mohamed El-Otmani, Moshe Negbi, and Eliezer E. Goldschmidt

Open access

Mohamed El-Otmani, Charles W. Coggins Jr., and Irving L. Eaks

Abstract

Relationships among fruit age, epicuticular wax, weight loss, internal atmosphere composition, and respiration were investigated in mature ‘Washington’ navel orange fruit [Citrus sinensis (L.) Osbeck]. Fruit epicuticular wax, internal CO2, and internal C2H4 increased, whereas as the season advanced, weight loss during storage and respiration decreased. Concomitantly, fruit conductance to CO2 was reduced. GA3 (10 ppm) application prior to fruit color break reduced the increase in epicuticular wax and thereby delayed the decrease of CO2 conductance, resulting in less of an increase in internal CO2. GA3-treated fruit were not consistently different for other parameters evaluated. Chemical name used: lα,2β,4aα,4bβ,10β)-2,4a,7-trihydroxy-l-methyl-8-methylenegibb-3-ene-l,10-dicarboxylic acid l,4a-lactone (gibberellic acid).