citrus, fruit are picked and placed into picking sacks; the fruit are dumped from the picking sacks into 10-box (40 kg per box) field tubs, which are mechanically hoisted and dumped into a field transport vehicle commonly referred to as a “goat.” The goat
Permeability to the postharvest fumigants ethylene dibromide (EDB) and methyl bromide (MB) varied among 10 plastic films tested on grapefruit (EDB) and oranges (MB). Permeability was determined by comparing fumigant residue levels in fumigated film-wrapped citrus fruit and fumigated nonwrapped fruit. Some films restricted passage of the fumigants to the fruit, and residue levels in fruit wrapped with these films were lower than in fumigated, nonwrapped fruit. Residue levels in fruit wrapped with other films were equal to those in fumigated, nonwrapped fruit and these films were judged to be highly permeable to the fumigants. EDB and MB residues were slightly higher in fruit wrapped with three of the films than those in nonwrapped fruit, indicating that these films were slightly less permeable to EDB and MB than to other films tested, and also that desorption of the fumigants from the fruit during post-fumigation aeration was slowed by these three films. The permeability of flexible polymer films to fumigants such as EDB and MB should be a prime consideration when selecting films for wrapping citrus fruit in quarantine situations.
Permeability to the postharvest fumigant hydrogen cyanide (HCN) varied markedly among 13 plastic film-wrapping materials. Permeability was determined by comparing California red scale [Aonidiella aurantii (Maskell)] (CRS) surviving fumigation on film-wrapped and nonwrapped, insect-infested, fruit. HCN transmission rates for several films also were determined by a permeation cell technique. Some films partially restricted passage of the fumigant to the fruit and CRS survival was high, while permeability of other films differed little from unrestricted exposure on nonwrapped fruit and CRS survival was low. For films with low permeability to HCN, increasing the HCN concentration or the length of fumigation time are possible methods of increasing the amount of HCN that penetrates to the fruit for control of quarantined insects. The permeability of film wrapping materials to fumigants should be a prime consideration when selecting films for wrapping citrus fruit in quarantine situations.
Arsenic compounds generate diverse effects in all living organisms. In citrus (Citrus L. sp.), they reduce acidity and improve fruit quality by unknown mechanisms. The major organic acid in citrus fruit is citric acid, which begins accumulating early in fruit development, reaches a peak in middle-sized fruit and then, in most species, declines as the fruit matures. In an attempt to understand the basis of the effect of arsenite, it was applied to `Minneola' tangelo (Citrus paradisi Macf. × C. reticulata Blanco) ≈6 weeks postanthesis, and a detailed analysis of total titratable acidity and citric acid concentration was performed throughout fruit growth. Within 35 days after arsenite application, total acid content and citrate concentration were slightly lower compared with the controls, and this difference persisted throughout fruit development. The concentrations of other organic acids were not reduced by the treatment. Sodium arsenite reduced the citrate concentration in `Eurieka' lemon callus [Citrus limon (L.) Burm.] also, without affecting tissue growth. Extractable activity of citrate synthase in treated fruit was inhibited within 1 day following arsenite spray, but recovered to a normal level a few days later. In contrast, gene expression was remarkably induced 1 day following treatment, which might explain the recovery in enzyme activity. Data suggest that reduction in acid accumulation may not be related to the initial inhibition of citrate synthase activity.
Methyl jasmonate (MJ) was tested as a potential abscission chemical to enhance mechanical harvest of `Hamlin' and `Valenica' orange [Citrus sinensis (L.) Osb.]. In field experiments, a solution of 1, 5, 10, 20, or 100 mm MJ was applied either as a stem wrap to individual fruit or as a spray to entire trees or canopy sectors. Solutions of 10, 20, and 100 mm MJ resulted in significant and consistent reduction of fruit detachment force and caused fruit drop within 7 to 10 days. Fruit loosening was preceded by an increase in the internal ethylene concentration of fruit similar to that of other experimental abscission compounds. While concentrations of 10 mm and less caused no or negligible phytotoxicity, solutions exceeding 10 mm MJ induced unacceptable levels of leaf abscission.
Grapefruit is weighed in air and water using the suspended weighing hook on the bottom of a top loading balance. Weight and volume of a fruit of any shape can be accurately determined in less than a minute.
Postharvest application of 500 ppm (2-chloroethyl)phosphonic acid (ethephon) induced degreening in ‘Bearss’ lemon at 15, 18 and 21°C, reducing the coloring time by 20 to 30%. Waxing delayed degreening slightly, but, on ethephon-treated fruit, degreening was as rapid or more rapid than on untreated, unwaxed fruit. Combination of thiabendazole (TBZ) with ethephon had little effect on the degreening rate. ‘Marsh’ grapefruit from an interior Florida grove was more responsive to ethephon than was fruit from an east coast grove. Waxing and TBZ treatments delayed degreening more in grapefruit than in lemon. Waxed east coast grapefruit did not satisfactorily degreen with or without the addition of ethephon. Degreening occurred in waxed ‘Hamlin’ orange and ‘Dancy’ tangerine, but color was not satisfactory, mainly because of poor carotenoid development.
Citrus trees were sprayed with ethephon when the fruit were mature but still green or partially degreened. Harvested fruit that were mature and partially or fully degreened were held in an atmosphere containing 10 ppm ethylene for 5 to 9 days. One preharvest ethephon spray hastened carotenoid accumulation in rinds of green ‘Nova’ tangerines, partially degreened ‘Robinson’ and ‘Dancy’ tangerines, and fully degreened ‘Robinson’ tangerines, but was not effective on green ‘Bearss’ lemons and partially degreened ‘Hamlin’ oranges. Effective concn varied between 50 and 500 ppm and with the cultivar evaluated. Two 500-ppm ethephon sprays, applied 2 weeks apart, hastened carotenoid accumulation in rinds of partially degreened ‘Hamlin’ oranges and ‘Robinson’ tangerines. Postharvest-ethylene treatment induced carotenoid accumulation in rinds of partially degreened ‘Bearss’ lemons and ‘Lee’ and ‘Dancy’ tangerines and degreened ‘Robinson’ and ‘Dancy’ tangerines. Tangerines showed greater ethylene-induced increases in rind carotenoids than did ‘Hamlin’ oranges and ‘Bearss’ lemons. Fruit which had higher rind carotenoid contents as a result of ethylene or ethephon application had better visible external color.
The acidless phenotype of the pummelo 2240 [Citrus maxima [Burro.] Merrill] is caused by a mutation affecting a key element of the citric acid accumulation pathway. To test the functionality of the tonoplast citrate transport mechanism, we obtained a tonoplast-enriched membrane fraction from juice tissues of acidless fruit by centrifugation through a discontinuous Ficoll gradient. The isolated tonoplast vesicles incorporated radioactively labeled citrate at a higher rate than vesicles from similarly fractionated high-acid fruit juice. Uptake of [14C]citrate occurred against a concentration gradient was stimulated by nitrate-sensitive ATP hydrolysis, but not by hydrolysis of PPi, and was not affected by the ionophore nigericin. Uptake was not inhibited by malate and only slightly by isocitrate. We did not find evidence of a defective citrate transport mechanism at the tonoplast of juice cells of acidless fruit. We propose that citric acid accumulation in the fruit of citrus is mediated by a carrier that uses energy produced during hydrolysis of ATP to transport citrate into the vacuole actively and specifically.
Moderate water stress applied to citrus trees can increase fruit °Brix. Florida citrus growers have been required to use less irrigation as competition for water increases. The goal of this study was to see if irrigation could be eliminated in the fall and winter with few negative consequences. Water stress was imposed over a 3-year period on `Hamlin' and `Valencia' oranges (an early and late variety, respectively) by stopping irrigation in late October and restarting it in March. `Hamlin' fruit was harvested after 2 months of stress and `Valencia' fruit was harvested after 4 to 5 months of stress. In most years, °Brix was increased by water stress. Over a 3-year period, `Hamlin' yield was not affected by the water stress, but `Valencia' yield decreased slightly in the 3rd year. The increase in °Brix is beneficial economically, and, over 3 cm of irrigation water per year can be saved.