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The effects of genotype and growth additives on the induction of embryogenesis from undeveloped ovules from mature fruit of Citrus were examined. Embryos were produced in cultures of 15 of the 17 representative polyembryonic cultivars examined. Cultured ovules of 5 monoembryonic cultivars did not become embryogenic. Percentages of ovules producing embryos in the responsive polyembryonic cultivars ranged from 5 to 20 after 56 days in culture. Mean numbers of embryos per responsive ovule ranged from 1.9 to 13.2. Effects of growth additives on the production of embryos from undeveloped ovules from mature fruit of ‘Marsh’ grapefruit were tested. A low concentration (0.01 mg/liter) of butanedioic acid mono (2, 2-dimethylhydrazide) (daminozide) was most effective at increasing the induction of somatic embryogenesis over the control treatment of 500 mg/liter malt extract. The presence of abscisic acid or a higher concentration of malt extract (100 mg/liter) in the medium also increased embryo induction, but germination of embryos obtained on the malt extract medium was poor. The use of undeveloped ovules from mature fruits allows the initiation of embryogenic cultures from a wide range of Citrus species.

Open Access
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Abstract

Ethephon was applied as a postharvest fruit dip to ‘Bearss’ lemons, ‘Robinson’ and ‘Dancy’ tangerines, ‘Hamlin’ oranges, and ‘Marsh’ grapefruit. Concentration as high as 8,000 ppm were used, and samples were held at 16, 21, and 27°C. Responses differed among cultivars, but were greater and more rapid as the temperature increased. Untreated fruit degreened more completely at 16° than at higher temperatures. At 21 and 27°, degreening usually was maximum with concentrations of 500 to 1,000 ppm. ‘Robinson’ tangerines responded to lower concentrations and showed increasing inhibition at levels from 2,000 to 8,000 ppm ethephon. In tangerines and grapefruit, degreening with ethephon approached that obtained with ethylene. Stem-end rot was increased by ethephon applications. These losses were greatest at the higher concentrations and temperatures, but they were lower and later than from ethylene degreening.

Open Access

Water loss was found to be a nondestructive indicator before visible symptoms of chilling injury (CI) in cold-stored grapefruit (Citrus paradisi Macf.) and lemon (C. limon L. Burm. f.). The water-loss rate increased significantly after removing the fruit from cold storage and holding at 20C. Scanning electron microscopy revealed large cracks around the stomata. Changes in electrical conductivity of the flavedo tissues, total electrolyte leakage, and K+ or Ca2+ leakage were all inadequate predictors of CI, appearing only after CI was evident.

Free access

`Eureka' lemons [Citrus limon (L.) Burro. f.] treated for commercial storage were held for 6 months at 13C. One-half of the fruits were individually sealed in high-density polyethylene (HDPE) plastic film and half not sealed. The HDPE-seaIed lemons showed little change in the water relations characteristics, while unsealed lemons lost weight and decreased in water potential throughout the storage period. The maturity indices in the two treatments were generally similar during the first 3 months of storage, after which maturation of wrapped fruit was slower than that of the control. The overall marketable quality of the fruit was higher in HDPE-sealed lemons than in unsealed. From these results, it appears feasible to introduce seal packaging in packing lines where lemons will be placed in extended storage.

Free access

Vacuolar acidification was investigated in `Palestine' sweet (Citrus limmetioides Tanaka) and `Persian' acid lime [(Citrus aurantifolia (Christm.) Swingle] (vacuolar pHs of 5.0 and 2.1, respectively) using tonoplast vesicles isolated from juice cells. The ATPase activity of tonoplast-enriched vesicles from sweet limes was strongly inhibited by bafilomycin A1 and NO3 -, but was unaffected by vanadate. In contrast, the ATPase activity in acid lime membranes was only slightly inhibited by bafilomycin A1 and NO3 - and was strongly inhibited by high concentrations of vanadate. The vacuolar origin of the acid lime vesicles was confirmed by immunoblotting. After solubilization and partial purification of the two enzymes by gel filtration, their inhibitor profiles were largely unchanged. Based on equal ATPase activities, vesicles from sweet and acid limes were able to generate similar pH gradients. However, in tonoplast vesicles from sweet limes, the maximum ΔpH was reached four times faster than in those from acid limes. Addition of ethylenediamine tetraacetic acid (EDTA) to chelate Mg+2 after the maximal ΔpH was attained resulted in collapse of the pH gradient in vesicles from sweet limes, whereas no change in ΔpH was observed in vesicles from acid limes, indicating a less H+ permeable membrane. Vacuolar ATPases from both cultivars exhibited identical pH optima and showed similar Mg+2 dependence, but only the acid lime ATPase activity was inhibited by Ca+2. These data confirm that the vanadate-sensitive form of the V-ATPase found in lemon and acid limes is specific to hyperacidifying tissues rather than to citrus juice cells. Sweet lime vacuoles bear the classical V-ATPase also found in vegetative plant tissues.

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`Oroblanco' is an early-maturing pummelo-grapefruit hybrid (Citrus grandis × C. paradisi). The fruit of this cultivar are usually picked in October and are marketed while their peel color is still green. However, during long-term storage, the fruit turns yellow, and loses much of their commercial value. In a previous study, we found that application of gibberellic acid and low storage temperatures of 2 °C (35.6 °F) markedly reduced the rate of degreening. However, `Oroblanco' fruit are sensitive to chilling injuries, and thus could not be stored at 2 °C for long periods. In the present study, we examined the possible application of intermittent warming (IW) and temperature conditioning (TC) treatments, in order to retain the green fruit color during long-term cold storage but without enhancing the development of chilling injuries. It was found, that following storage at 2 °C, either with or without IW and TC, the fruit retained green color up to 16 weeks, whereas at 11 °C (51.8 °F) fruit turned yellow after 8 weeks. However, untreated fruit held continuously at 2 °C developed 40, 51, and 68% chilling injuries after 8, 12, and 16 weeks, respectively. IW (storage at cycles of 3 weeks at 2 °C + 1 week at 11 °C) reduced the amount of chilling injuries to only 5, 7 and 11% after the same periods of time, respectively. TC [a pre-storage treatment for 7 days at 16 °C (60.8 °F) before continuous storage at 2 °C] effectively reduced the development of chilling injuries to only 5% after 8 weeks of storage, but was ineffective in reducing chilling damage after longer storage periods. Because chilling damaged fruit is prone to decay, the IW and TC treatments also reduced the incidence of decay development during storage. The IW and TC treatments did not affect juice total soluble solids and acid percentages, but did affect fruit taste and the amounts of off-flavor volatiles emitted from the juice. Taste panels indicated that the taste score of untreated control fruit stored at 11 °C gradually decreased during long-term storage, and that this decrease was more severe in chilling damaged fruit stored continuously at 2 °C. The taste of IW-treated fruit remained acceptable even after 16 weeks of storage, and TC-treated fruit remained acceptable for up to 12 weeks. Fruit taste scores were inversely correlated with the concentrations of ethanol and acetaldehyde detected in the juice headspace.

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Abstract

‘Hamlin,’ ‘Pineapple,’ and ‘Valencia’ oranges and ‘Marsh’ grapefruit were harvested by hand and with either the limb clamp shaker, foliage (coil) shaker, or vacuum tube picker's aid. Harvesting trials were combined with tests of abscission sprays, pre- and postharvest fungicides, and simulated fresh fruit marketing. All mechanical shaker harvesting increased losses from cuts and punctures, but “plugging” was so reduced that percentage of sound fruit sometimes did not differ significantly from that in the hand picked controls. When mechanical harvesting was followed by the fungicide thiabendazole (TBZ) decay in ‘Hamlin’ oranges during simulated fresh fruit marketing was not significantly higher than in the hand harvested controls treated with diphenyl only. Mechanically harvested fruit from trees sprayed with benomyl (Benlate) always had less decay than hand harvested fruit without the benomyl spray, differences usually being significant. Abscission sprays were helpful only for crops intended for cannery use. Long stems on mechanically harvested fruit remain a problem.

Open Access
Authors: and

Abstract

Light-reflectance measurements at 648-740 and 674-740 nm decreased as chlorophyll was lost during the maturation and degreening of citrus fruits. The difference between these measurements changed as the chlorophyll level declined. This change was shown as an initial decrease followed by an increase in 648-674 nm measurements. Analyses of rind samples revealed changes in the relative concentration of chlorophyll a and b and consequent decreases in the a/b ratio as total chlorophyll levels decreased. Formulas were developed to convert light-reflectance readings at 674-740 and 648-740 nm to concentration of chlorophyll a and b in the tissue. The greater resistance of chlorophyll b to degradation during color development may explain the difficulty of satisfactorily degreening some fruit and may serve as a basis in selecting for improved coloring characteristics.

Open Access
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Abstract

Abscisic acid (ABA) introduced through the stem of ‘Pineapple’ and ‘Valencia’ oranges stimulated cellulase activity in the separation zones. ‘Pineapple’ orange was affected more than ‘Valencia’. Cellulase activity was greatest under normal atmospheres in which ethylene accumulated in the treated fruit. Under one-fifth atmosphere with little ethylene accumulation, cellulase was 2 to 2.5 times greater in separation zones of treated fruit than in non-treated fruit. ABA introduced through the stem was more effective than spray applications. ABA sprayed on the fruit was partly absorbed but did not increase ethylene production or cellulase activity, or decrease fruit removal force.

Open Access
Authors: and

Abstract

Healing of minor injuries to ‘Valencia’ orange (Citrus sinensis (L) osbeck) occurs rapidly at 30°C and 96-98% relative humidity. It is manifested by a marked increase in the activity of phenylalanine ammonia-lyase (PAL) and deposition of lignin. PAL activity is confined mainly to injured flavedo while uninjured peel and albedo tissues exhibit very little activity. Inoculation of injured flavedo, immediately after injury, with P. digitatum sacc. disrupts the increase in PAL activity. When acetone powder from decayed peel was mixed with that of healed injured fruit and enzyme preparation was made from the mixture, there was no apparent reduction in phenylalanine ammonia-lyase activity, except that cuased by dilution. The synthesis of both PAL and lignin in mature fruit is strongly inhibited by cycloheximide, but not by actinomycin D.

Open Access