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  • Author or Editor: Roger Young x
  • Journal of the American Society for Horticultural Science x
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Abstract

Seedlings of 18 citrus types were exposed to artificial hardening conditions. ‘Nagami’ kumquat, false hybrid satsuma and ‘Cleopatra’ mandarins were the most cold hardy and ‘Lisbon’ lemon, ‘Mexican’ lime, Rangpur’ lime, and ‘Calamondin’ hybrid kumquat the least cold hardy. Three mandarins, 1 tangelo, 3 oranges, and 4 grapefruit types were intermediate in hardiness. Generally, the most hardy types hardened some at 70° day and 50°F night temperatures, and 60°/40° as well as at lower temperatures while the least hardy types hardened primarily at 50°/30° and 45°/26°. Sugar accumulation was associated with hardening.

Open Access
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Abstract

‘Redblush’ grapefruit seedlings were exposed to hardening temperatures in the presence and absence of light. Both reducing and non-reducing sugars increased in leaves and wood of hardened plants and non-reducing sugars increased in roots of hardened plants. The primary sugars involved were glucose, fructose, and sucrose. Plants exposed to hardening temperatures in the dark did not harden, and water soluble proteins did not materially change in the leaves during hardening in the light.

Lower temperatures were required to kill leaves without ice on the surface than with ice, and lower temperatures were required to kill hardened leaves. Hardened leaves developed a small capacity to recover from cell dehydration due to ice nucleation indicating changes in protoplasm stability and membranes during hardening

Open Access
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Abstract

Citrus seedlings sprayed with chemicals which influence the cold hardiness of other plants were hardened in controlled conditions. Maleic hydrazide (MH-30) increased cold hardiness; however, growth retardants (2-chloroethyl)trimethylammoniumchloride (chlormequat) and succinic acid-2,2-dimethylhydrazide (SADH), and growth inhibitor abscisic acid (ABA) did not. ABA at high concns decreased cold hardiness as did gibberellic acid (GA3). Benzyladenine (BA), kinetin (KN), decenylsuccinic acid (DSA), and (2-chloroethyl)phosphonic acid (ethephon) had little or no effect on cold hardiness. These results are consistent with tests on citrus conducted under field conditions.

Open Access
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Abstract

Freeze-injured citrus fruit produced above-normal amounts of ethylene 1 to 4 days after injury. Elevated ethylene levels were often found in fruit 3 weeks after injury. Cellulase activity in the abscission zone increased 4 to 8 days after injury and preceded abscission. Some severely injured fruit that did not abscise were responsive to abscission-inducing chemicals. High internal ethylene content did not correlate as well with abscission as did high rates of abscission-zone cellulase activity.

Open Access
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Abstract

Early in the season, postharvest applications of 2-(4-chlorophenylthio)-triethylamine (CPTA) had little effect on carotenoid synthesis in ‘Bearss’ lemon (Citrus limon Burm. f.), ‘Robinson’ tangerine (C. reticulata Blanco × (C. paradisi Macf. × C. reticulata)), ‘Marsh’ grapefruit (C. paradisi Macf.), and ‘Hamlin’ orange [C. sinensis (L.) Osbeck]. The responses increased as the fruit matured, but greater CPTA responses were induced by storage of the fruit at 16°C before treatment or by exposing treated fruit to ethylene. Observations suggested that cultivars with low natural carotenoid levels (lemon and grapefruit) are more responsive to CPTA applications than are those with higher levels (tangerine). Improved color of ‘Hamlin’ orange was obtained with CPTA applications made before or after a 3-day degreening treatment. This response did not appear to be prevented by waxing. However, the practical use of CPTA to improve the color of oranges appears limited, although it may be useful in research on carotenoid synthesis.

Open Access
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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

‘Redblush’ grapefruit seedlings, with and without leaves, were sprayed 1 to 5 times with 100 to 1000 ppm abscisic acid or 500 to 3000 ppm cycocel. Plants were subsequently exposed to several day/night temperature regimes which included 70°/50°, 90°/70°, and 95°/95°F. Both abscisic acid and cycocel delayed bud growth of leafy and defoliated seedlings. Abscisic acid was more effective than cycocel, and both compounds were most effective in delaying bud growth at lower temperatures, higher concentrations, and with more than one application. Abscisic acid was more toxic than cycocel, and both compounds were more toxic to defoliated plants than to leafy plants. Gibberellic acid overcame a correlative bud inhibition by the leaves, and abscisic acid decreased the effect of gibberellic acid.

Open Access
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Abstract

(2-chloroethyl)phosphonic acid (ethephon) applied as a preharvest spray at rates of 200, 300, and 500 ppm induced significant on-the-tree degreening of fruit of ‘Robinson’, ‘Lee’ ‘Nova’, and ‘Dancy’ tangerines and ‘Hamlin’ oranges. Greatest degreening occurred 2 to 6 days following application and subsequent to peak-ethylene evolution. Fruit which were partially or totally degreened on the tree required less postharvest degreening and showed less decay in storage than untreated fruit. Ethephon applied at 200 to 500 ppm induced varying degrees of fruit loosening and, often, fruit drop. Generally, less than 10% ofthe leaves abscised on all cultivars with rates under 200 ppm and on ‘Nova’ and ‘Dancy’ tangerines and ‘Hamlin’ oranges with rates under 500 ppm. Considerable leaf abscission occurred on ‘Robinson’ and ‘Lee’ tangerines treated with 300 and 500 ppm ethephon.

Open Access
Authors: and

Abstract

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.

Open Access

Abstract

Tests of citrus seedlings exposed to a series of hardening temperatures showed that kumquat, Fortunella hindsii (Champ.) Swing., acquired more hardiness at 21°/10°C than did ‘Redblush’ grapefruit, Citrus paradisi Macf., or citron, C. medica L. After 8 weeks’ hardening kumquat was the most cold hardy; citron, the least. Leaf photosynthetic CO2 uptake decreased, and leaf diffusion resistance (sec/cm) increased with hardening in all cultivars, but did not reflect the degree of hardening attained. Stomatal closure during hardening was not caused by moisture stress. Ethylene evolution from leaves did not change during hardening of kumquat, mandarin, C. reticulata Blanco, or grapefruit, but did increase from hardened citron leaves.

Open Access