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- Author or Editor: S. P. Monselise x
Abstract
GLC analysis of organic acids of different fruit components (flavedo, albedo, and juice) was carried out by a modified method. ‘Shamouti’ orange fruits (Citrus sinensis (L.) Osbeck) were of different viability because of progressive aging during postharvest storage (3 months at 17°C). Wide quantitative and qualitative differences in acid composition of tissues were detected. Citric was the main acid in juice, malonic and malic in peel tissues. Additional acids included succinic, adipic, isocitric, oxalic, lactic, aconitic, α-ketoglutaric and benzoic. With tissue aging, malonic, succinic and adipic acids concentration increased in peel and juice, but citric and malic acids concn decreased in juice. Malonic acid, the competitive inhibitor of acid respiration, can serve as an indicator of fruit tissue senescence, because its accumulation in the peel begins at fruit maturity, and increases threefold during 3 months post harvest. Moreover, it is the acid component most closely linked with aging of fruit tissues as determined by softness and deformation parameters.
Abstract
One early treatment (late May) with 25 ppm gibberellic acid (GA3) strongly depressed summer and fall bloom and resulting off-season fruits of ‘Temple’ orange (Citrus reticulata Blanco × C. sinensis (L.) osbeck). A late June treatment failed to repress and even tended to increase the number of off-season fruits. A repeated treatment at both dates, had a smaller effect than a single early treatment. A possible effect of a late GA application on the persistence of off-season fruitlets is suggested. Girdling of a part of scaffold branches gave a response similar to that of the early GA treatment.
Abstract
(2-Chloroethyl)phosphonic acid (ethephon), 200 ppm, and naphthaleneacetic acid (NAA), 350 ppm, sprayed on fruitlets 1 cm in diameter, caused satisfactory thinning of heavily loaded ‘Wilking’ mandarin trees (Citrus reticulata Blanco) without significant decrease of yield in kg per tree. Individual fruit size was increased 64% with ethephon and by 48% with NAA, increasing profit by about 30% in both cases as compared with hand thinned controls. A summer pruning treatment had similar effects but the increase in fruit size was smaller. Ethephon reduced alternation of bearing and resulted in satisfactory yields the following year on 57% of the treated trees.
Abstract
External peel color and the content of chlorophyll, total carotenoids, carotenes and xanthophylls in the flavedo of ‘Shamouti’ orange fruits were studied during their development from the young to the overripe fruit stages.
In the early stage, the main change consisted of a decrease in chlorophyll content, resulting in the initial yellowing of the peel. Later, concomitant with the appearance of the typical orange color (color break), total carotenoid content of flavedo, as well as its carotene/xanthophyll ratio increased rapidly. Such increase, however, continued after full color had been attained and until the fruit was decidedly overripe. The advantage of relating the pigment content to the flavedo layer rather than to the whole peel and the suitability of expressing the pigment concentration on a per cm2 basis are discussed briefly.
Abstract
Girdling followed by reopening of the girdle (late in June and July) increased fruit size on mature trees of grapefruit (Citrus paradisi Macf.) while effects of 1 or 2 applications of 2,4-dichlorophenoxyacetic acid (2,4-D) superimposed in a factorial layout were marginal. Girdling caused some delay in fruit maturation as did the 2,4-D applications. Girdling caused no apparent damage to trees the following year.
Abstract
Studies of pollen germination, stigmatic treatments and a field experiment were conducted in an attempt to decrease seed number of mandarin-type fruits (Citrus reticulata Blanco cv. Dancy and C. reticulata Blanco cv. Temple). Gibberellin (GA3) in the medium inhibited germination only above 250 ppm; cycloheximide inhibited it at 0.1 ppm. Treatments of the above and other compounds applied to stigmatic surfaces decreased either set or yield. Field treatments with 20 ppm GA at early- or mid-bloom or 150 ppm naphthaleneacetic acid (NAA) applied when fruitlets were 5 or 10 mm in diameter alone or in combinations, decreased seed number to 72% for ‘Dancy’ and 82% for ‘Temple’. Effects of NAA were greater than for GA. Neither treatment caused thinning. Instead, fruit number and yields increased, while fruit size decreased slightly. Bioassays of NAA-treated fruitlets showed residual active NAA 25 days after spraying as well as an increase in native gibberellin-like activity which was highest in NAA + GA-treated fruitlets.
Abstract
Excessive rough and thick peel, linked with large fruit sizes is found in ‘Shamouti’ oranges (Citrus sinensis (L.) Osbeck) grown under marginal soil and climatic conditions. This condition was overcome by early (April-May) sprays of succinic acid-2,2-dimethylhydrazide (SADH) and 2-chloroethyltrimethylammonium chloride (CCC, chlormequat), probably counteracting high endogenous promotors found in rough tissues. While SADH is too expensive to be profitable and it usually decreases fruit size, CCC can be used without this effect and is commercially rewarding.
Abstract
A previous report that girdling at the beginning of bloom increases yield of orange trees by increasing fruit number but not fruit size has been confirmed. Girdling caused the abortion of some flowers which were in the early differentiation stages at girdling time, and decreased the drop of ovaries during the first portion of the shedding season. Thus fewer flowers produced more fruits. Since it has been shown that girdling increases gibberellin activity in the aerial parts, the dual effect of gibberellin on flower formation and fruit setting may explain these influences of girdling.
Abstract
Corky (silvery) spots of ‘Marsh’ grapefruit (Citrus paradisi Macf.) were substantially reduced by application of 16-22 ppm 2,4-dichlorophenoxy acetic isopropyl ester on developing fruitlets (May to July) or of 20 ppm gibberellin A3 in June. Success is probably due to enhanced growth potential of external fruit layers, preventing their splitting due to internal pressure.
Abstract
Paclobutrazol (PP333) [(2RS,3RS)-l-(4-chlorophenyl)-4, 4-dimethyl-2-(l,2,4-triazol-l-yl-)pentan-3-ol] sprays applied to ‘Minneola’ tangelo trees, at 500 or 1000 ppm, before the onset of summer flush, markedly reduced total growth, number of shoots, and internode length. Soil treatments (0.4 and 0.8 g per square meter) had only a small effect, probably because of the short time from application to flush inception. Sprays of Morphactin (an auxin transport inhibitor), at 250 and 500 ppm did not reduce growth, but rather enhanced it by increasing the number of emerging shoots. The spring flush of the same trees also showed effects of paclobutrazol soil treatments, whereas other treatments were not different from control. Paclobutrazol sprays on comparable ‘Minneola’ trees just before the spring flush also reduced this growth. Paclobutrazol may become a tool for the control of vegetative growth of mature citrus trees.