Search Results
Abstract
Instrumental methods evaluated for effectiveness in following color changes in ripening tomato fruit (Lxcopersicon esculentum Mill.) included a light-reflectance and 2 light-transmittance sample systems. Each system was tested with wavelength pairs of 500–595, 540–595, and 595–650 nm. Instrument methods, with appropriate photomultipliers, generally were more sensitive to color changes than were visual observations. The light-transmittance systems were also more sensitive to small changes than the light-reflectance system. However, with all systems, measurements at 595 650 nm were highly correlated with visual color ratings during ripening. Light-transmittance measurements at 540–595 nm were effective in detecting changes at an earlier ripening stage than either reflective or visual observations. Because of complex pigment changes, this measurement increased rapidly during initial ripening stages, and then decreased during later stages, making it more difficult to relate to visual color.
Abstract
Citrus trees were defoliated to obtain measurements of radiation penetration at various canopy densities. Tree size measurements were used to calculate the leaf-area index (LAI) and leaf-area to canopy-area ratio (LAC) of trees. Penetration of photosynthetically active radiation (PAR) increased curvilinearly as defoliation increased and LAC decreased. Observed relationships between PAR penetration and LAC were used to estimate LAC values from PAR penetration measurements. Correlations between PAR penetration and LAC were slightly higher than with LAI. LAI and LAC appeared to vary independently from tree size as measured by tree diameter or leaf area.
Abstract
Young ‘Dancy’ tangerine (Citrus reticulata Blanco) fruit were thinned with 200 to 250 ppm (2-chloroethyl)phosphonic acid (ethephon) sprays. Ethephon treatments that thinned fruit to an average of about 1 per twig generally increased fruit size and crop value and reduced alternate bearing. Thinning was less effective under water stress conditions. Little or no leaf abscission was observed, even under dry grove conditions. Ethephon was most effective when it was applied near the end of the natural drop period in May, but before many of the fruit became larger than 15 mm in diameter. Gibberellin (GA3 or GA4,7) and/or 6-benzylamino purine (BA) did not reduce flowering or fruiting.
Abstract
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.
Abstract
‘Hamlin’ oranges were washed by hand or with various mechanical-washer procedures. The latter included variations in washing and brushing time and brush-bristle size. Washing procedures had little effect on subsequent chlorophyll loss during degreening. Carotenoid synthesis was significantly reduced by washing before degreening. These reductions in carotenoid levels were not appreciably affected by changes in washing time or brush-bristle size. Hand-washing oranges with a sponge reduced carotenoid synthesis less than mechanical washing. Carotenoid synthesis was reduced by less brushing than was required to clean the fruit, but “over” brushing had little further effect.
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.
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.
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.
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.
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.