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- Author or Editor: R. Hilton Biggs x
The effect of wounding and abscission-accelerating compounds on ethylene production in ‘Valencia’ orange (Citrus sinesis (L.) Osb.) was studied using enclosed peel explants. Three peel disks, 10 mm in diameter, produced a maximum of about 5.5 nl hour ethylene during the second day after excision from the fruit. Higher rates of ethylene production were observed in albedo than in flavedo tissue from 30 to 72 hours after excision. Treatment with the abscission accelerant 5-chloro-3-methyl-4-nitro-l H-pyrazole (Release) more than doubled ethylene production, an effect which was prevented by cordycepin. Inhibition of ethylene production by rhizobitoxine and cycloheximide indicated that ethylene production induced by either physical or chemical wounding in citrus peel proceeds from methionine and has requirements similar to those of other tissues.
Temperature effects on glyoxal dioxime (Pik-Off) stimulation of ethylene production and fruit loosening and on uptake of 14C-glyoxal dioxime were investigated using ‘Hamlin’ oranges [Citrus sinensis (L.) Osb.] harvested with petioles attached. Oranges treated with 250 ppm glyoxal dioxime produced significantly more ethylene than untreated fruit at 20, 25, and 30°C but not at 10 or 15°. Fruit loosening was correlated with internal ethylene concentration, producing a significant loosening effect for glyoxal dioxime at 20, 25, and 30°. Lack of effectiveness of glyoxal dioxime for inducing fruit loosening at low temperatures (10 and 15°) cannot be explained by a reduced rate of uptake but may result from impairment of ethylene biogenesis by fruit tissue.
‘Valencia’ oranges (Citrus sinensis (L.) Osbeck) damaged with rust mite (Phyllocoptruta oleivora Ashmead) responded to the abscission-accelerating chemical glyoxal dioxime (ethanedial dioxime) with greater ethylene production and greater reduction in bonding force than undamaged fruit. More than 90% of the 14C-glyoxal dioxime taken up by the rind was absorbed during the first 24 hrs. Absorption of 14C-glyoxal dioxime by rind tissue of mite-damaged fruit was more rapid than that of undamaged fruit. The differences in uptake of 14C-glyoxal dioxime due to mite damage were greatest on the first day after treatment, which was also the time of maximum ethylene production in response to glyoxal dioxime. The increased uptake in mite-damaged fruit is partially responsible for the increased effectiveness of glyoxal dioxime. It is likely that mite-damaged fruit are more permeable to many agricultural chemicals than undamaged fruit.
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.