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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
Authors: and

Abstract

Sour orange leaves (Citrus aurantium L.) from cold-hardened and unhardened plants were sectioned and prepared for light and electronmicroscopy examination after freezing at -3.3°C and -6.7°. Severe membrane destruction was visible in both hardened and unhardened cells after freezing. These membranes included the tonoplast, outer chloroplast membrane, and the cristae membrane in the mitochrondria. The thylakoids of the grana, the intergrana lamella, and the outer mitochrondrial membranes remained intact. Membrane destruction resulted in gross disorganization of cell contents. Disruption of cells was evident and included palisade and mesophyll cells, the lower epidermal layer, and xylem, fiber, and pith cells in the vascular system.

Open Access
Authors: and

Abstract

Preharvest applications of (2-chloroethyl)phosphonic acid (ethephon) on ‘Bearss’ lemons were relatively ineffective for inducing degreening or abscission. This was not due to lack of absorption or ethylene production. Similar rates of application as a postharvest dip induced degreening, suggesting that a factor from the tree inhibited the response to ethylene. This possibility was supported by data from further tests on ‘Bearss’ lemons and on ‘Robinson’, ‘Lee’, and ‘Dancy’ tangerines and ‘Hamlin’ oranges. Degreening and abscission responses to ethephon in detached fruit or fruit on which the stem was girdled were greater than in fruit on the tree. Applications of gibberellic acid retarded these responses. The results varied among cultivars and between the degreening and abscission responses. However, the general response pattern suggests that the tree provides a factor (or factors) which, on translocation to the fruit, inhibits degreening and abscission. This inhibitory factor may be a growth promoter such as auxin, gibberellin, or cytokinin.

Open Access

Abstract

The flesh of ‘Redblush’ grapefruit exposed to 41.8°C day/36.1°C night temperatures in environmental growth chambers for 60 days did not increase in lycopene content, while fruit exposed to natural conditions in sunlight and under shade did. Lowering the temperature from 41.8°C/36.1°C to 32.2°C/21.1°C produce a high level of lycopene. Carotene concns. of fruit exposed to 41.8°C/36.1°C and natural conditions remained the same. Exposure to 32.2°C/21.1°C caused a small increase in carotene, while exposure to natural conditions, at lower temperatures, caused a larger increase in carotene.

Open Access

Abstract

14C-Ethylene was the major breakdown product of 1,214C-(2-chloroethyl)phosphonic acid (ethephon)-treated fruit and leaves of several Citrus taxons. Neither 14CO2 nor other by-products were detected. Most of the nonethylene radioactivity recovered was from tissue surfaces. Radioactivity was not readily translocated from leaves or fruit.

Open Access

Abstract

Sweet orange cultivars, Citrus sinensis (L.) Osbeck, in several stages of blight (young tree decline) were studied for characteristics of waterflow or uptake. Many small and major roots and the trunk on moderately blighted trees had restricted waterflow or uptake capabilities. Some small and major roots on the blighted side of early-stage or sectored trees also had restricted waterflow or uptake capabilities, but the healthy side roots functioned similarly to those on healthy trees. Dye uptake patterns confirmed that the waterflow or uptake was restricted in the diseased portions of the trees. On moderately blighted trees, young xylem appeared to be more functional for water movement than older xylem. Necrotic roots were found on the blighted side of early-stage sectored trees and moderately blighted trees, but not on the healthy side of sectored trees or on healthy trees. The sectoring type of early blight expression affords a model system for study whereby both blighted and apparently healthy tissues occur on the same tree.

Open Access

Abstract

‘Redblush’ grapefruit borne on young fruiting trees and grafted on sour orange seedlings were exposed to natural and artificial climates. Fruit exposed to artificially controlled and naturally occurring minimum night temperatures above 70°F, combined with high day temperatures, had high Brix contents, low acid, and thin but green peels. Fruit exposed to minimum night temperatures below 60°, combined with moderate to cool day temperatures had both high Brix and acid and thicker but better colored peels. Cool temperatures in the late fall after hot summer and early fall conditions aided in thickening and coloring of peels of fruit which had already attained high Brix and early maturity.

Open Access

Abstract

In an assessment of natural hazards on world crop production, an average of more than $ 100 million per year is lost in the continental United States due to freeze damage to 22 major crops. The greatest loss is in citrus production and amounts to about one-third of the national average. A severe freeze occurred in 1962 which cost Florida more than one-third of its total production, in excess of 10 million boxes (41 kg.) of fruit and onefourth of its 52 million trees. Similar losses occurred again in 1977 and, most recently, in 1981 and 1982. These losses impact negatively not only on the present and future economic stability of an industry, but also in meeting the dietary needs (supply and nutrition) of an expanding world population, which is facing ever-increasing uncertainties in adequate nutrition and subsistence levels.

Open Access

Abstract

2-Chloroethylphosphonic acid (Ethrel) applied at 50 to 200 ppm as a preharvest spray, showed considerable promise in degreening ‘Robinson’ and ‘Lee’ tangerine fruit. The preharvest degreening resulted in less postharvest degreening time required for acceptable color and less fruit decay during storage. Ethrel concn between 100 and 200 ppm caused abscission of some old leaves, but had no apparent effect on external appearance other than color.

Open Access