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Growth and topological indices of `Eureka' lemon were measured after 6 months in well-watered and well-fertilized conditions and factorial combinations of moderate (29/21C day/night) or high (42/32C day/night) temperatures and ambient (350 to 380 μmol·mol) or elevated (constant 680 μmol·mol-1) CO2. In high temperatures, plants were smaller and had higher levels of leaf chlorophyll a than in moderate temperatures. Moreover, plants in high temperatures and elevated CO2 had about 15 % higher levels of leaf chlorophyll a than those in high temperatures and ambient CO2. In high temperatures, plant growth in elevated CO2 was about 87% more than in ambient CO2. Thus, high CO2 reduced the negative effect of high temperature on shoot growth. In moderate temperatures, plant growth in elevated CO2 was only about 21% more than in ambient CO2. Irrespective of temperature treatments, shoot branch architecture in elevated CO2 was more hierarchical than those in ambient CO2. Specific shoot extension, a topological measure of branch frequency, was not affected by elevated CO2 in moderate temperatures, but was increased by elevated CO2 enrichment in high temperatures-an indication of decreased branch frequency and increased apical dominance. In moderate temperatures, plants in elevated CO2 had fibrous root branch patterns that were less hierarchical than at ambient CO2. The lengths of exterior and interior fibrous roots between branch points and the length of second-degree adventitious lateral branches were increased >50% by high temperatures compared with moderate temperatures. Root length between branch points was not affected by CO2 levels.
Abstract
Leaves of cold-acclimated lemon [Citrus limon (L.) Burm. f.], grapefruit (C. paradisi Macf.), orange [C. sinensis (L.) Osbeck], and mandarin (C. unshiu Marc.) trees ranged in cold hardiness from −4 to −11°C. No significant differences in water content (g H2O/g dry weight) or melting point depression were observed. Plots of liquid water content during freezing (g H2O/g dry weight) vs. temperature were similar for the 4 citrus species. The tissues apparently deviated from ideal freezing behavior because less ice was formed. The reduced ice formation could not be accounted for by osmotic effects. Negative pressure potential developed during freezing is hypothesized to play a role in tissue water potential in frozen systems. It was concluded that hardier Citrus leaves survive freezing of a larger fraction of their tissue water.
Protoplasts isolated from an embryogenic callus line of `Femminello siracusano' lemon [Citrus limon (L.) Burm. f.] were incubated with 0.5 μm toxin of Phoma tracheiphila (Petri) Kanc. et Ghik., the pathogen of the mal secco disease, which seriously damages most commercial lemon cultivars. Two toxin-tolerant cell lines were obtained, and plants were regenerated from each line. The selected protoclones were tested for their tolerance by exposing callus and protoplasts to the toxin and detecting chitinase (a pathogenesis-related protein) among the intra- and extracellular proteins extracted from leaves of regenerated plants and suspension culture, respectively. The tolerance of the protoclones in these tests was equivalent to the tolerant lemon cultivar Monachello, and they were substantially more tolerant than their mother cultivar Femminello siracusano.
Abstract
Conventional degreening of fruits of lemon [Citrus limon (L.) Burm f.] by ethylene gas or treating with the ethylene-releasing agents (2-chloroethyl) phosphonic acid (ethephon) or 2-chloroethyl-tris(2-methoxyethoxy)silane, aggravates the development of various blemishes resulting, at times, in a loss of more than half of the fruit. Seal-packaging of lemons in 10 μm-thick film of high-density polyethylene (HDPE) markedly inhibited the development of blemishes. After 3 weeks’ storage, fruit commercially degreened with ethylene was 19.8 % blemished when unpackaged and 6.3% blemished when sealed in HDPE. Furthermore, this treatment delayed deterioration of fruit for a period longer than 6 months, much beyond that required for marketing. Spoilage resulting from blemishes, decay, softening, or overripe-coloration was much lower in sealed than in the non-sealed fruit. The combination of treatment with ethylene-releasing agents and HDPE seal-packaging permits degreening of lemons.
Abstract
Three auxins (4-amino-3,5,6-trichloropyridine-2-carboxylic acid; 3,5,6-trichloropyridine-2-oxyacetic acid; and 4-chlorophenoxyacetic acid) and 2 inhibitors of ethylene biosynthesis (i.e., aminoethoxyvinylglycine and aminoxyacetic acid) have been shown to inhibit abscission of stem parts (buttons) from fruit of lemon (Citrus limon Burm. f.) stored in controlled ethylene (about 5 ppm) atmosheres. Freshly picked lemons were treated by dipping them in aqueous solutions containing 500 ppm Triton X-100 plus-or-minus additions and then were stored at a packing house for 13 days; the fruit then were color-stored and analyzed for evidence of button abscission. When the abscission inhibitors were tested in concentrations equal to or greater than commercial concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) (2|0 ppm) and its isopropyl ester (250 ppm), only 4-amino-3,5,6-trichloropyridine-2-carboxylic acid (picloram) was found to be as effective in inhibiting button abscission. As little as 50 ppm picloram gave inhibition of abscission comparable to 250 ppm isopropyl ester of 2,4-D. All of the auxin inhibitors of button abscission including the free acid and isopropyl ester of 2,4-D delayed the degreening of fruit in the packing house. Triclopyr (3,5,6-trichloropyridine-2-oxyacetic acid) had the severest effect, picloram had a moderate effect, and the free base and isopropyl ester of 2,4-D had mild delaying effects on degreening. Aminoethoxyvinylglycine (200 ppm) and aminoxyacetic acid (1840 ppm) did not inhibit degreening.
Abstract
Seal packaging of orange [Citrus sinensis (L.) Osbeck cvs. Valencia and Shamouti], grapefruit (Citrus paradisi Macf. cv. Marsh) and lemons (Citrus limon Burnt, f. cv. Eureka) with high-density polyethylene (HOPE) film (0.01 mm in thickness) delayed softening and inhibited weight loss and deformation of the fruit more than cooling. Sealed fruit at 20°C and 85% relative humidity (RH) had better appearance and were firmer than non-sealed fruit at their lowest temperature possible without chilling injury and 85–90% RH. HOPE seal-packaging also inhibited chilling injury of grapefruit and lemons stored at 5° and 2°C, respectively. The C02 content of grapefruit was unaffected by seal-packaging, hut it was lower at cooler temperatures. Decay of citrus fruit depended more on the storage temperature than on the type of packaging. However, in storage up to 1 month, no significant difference was found in most experiments in decay percentage between orange, grapefruit, and lemon sealed with HOPE and stored in a packing house (13 to 25°C), and non-sealed fruits, at the lowest temperatures possible without chilling injury of 2, 10 and 14°C, respectively.
Abstract
The respiration, ethylene production and ethylene, ethyl alcohol, and acetaldehyde content of the internal atmosphere of citrus fruit increased at 20°C following exposures to chilling temperatures (0° and 5°) compared with fruit placed directly at 20°C. The increases were greater the longer the exposure and greater following exposure to 0° than following exposure to 5°. Exposure to 12.8°, a nonchilling temperature, did not elicit a stimulation of these attributes when transferred to 20°. Ethylene, ethyl alcohol, and acetaldehyde in the internal atmosphere of fruit remained at the same levels during the chilling exposures. During storage at 12.8° the acetaldehyde content in the internal atmosphere increased, but the ethylene and ethyl alcohol content did not. The chilling injury sustained by citrus fruit during storage could be evaluated by transferring samples to 20° and determining the respiratory rate, ethylene production or the volatile content in the internal atmosphere 24 hours after transfer to 20°.
Abstract
Seal-packaging of individual fruits of ‘Shamouti’ and ‘Valencia’ oranges (Citrus sinensis L. Osbeck), grapefruit (C. paradisi Macf cv. Marsh) and lemons (C. limon Burm. f. cv. Eureka) with a film of high-density polyethylene (0.01 mm) markedly delayed their deterioration as measured by peel shrinkage, softening, deformation and loss of flavor. This film was applied to fruit that had received conventional treatments of disinfection with sodium orthophenylphenate and waxing. Sealed fruit maintained their fresh appearance more than twice as long as conventionally handled fruit. Weight loss of fruit was reduced about five-fold. Sealed fruit at 20° were firmer and lost less weight than non-sealed fruit at the lowest optimal temperature. Sealing various citrus fruits in high density polyethylene reduced both their respiratory activity and ethylene production. CO2 and O2 content in the internal atmosphere of the sealed and control fruit were similar but ethylene content was lower in the sealed fruit.
Tree growth, yield, and fruit quality of eight lemon cultivars [Citrus limon (L.) Burro. f.] on macrophylla (Alemow) (C. macrophylla Wester) rootstock were compared when grown in sandy soil in the arid climate of south-western Arizona. `Foothill Lisbon' had higher cumulative yield and titratable acids than `Monroe Lisbon', `Prior Lisbon', `Eureka', and `Villafranca', and had larger fruit than other `Lisbon' cultivars. `Prior Lisbon' produced a larger tree canopy with lower yield efficiency than all other cultivars and did not show any decline due to sieve tube necrosis 12 years after planting. Overall, `Eureka' cultivars and `Villafranca' had lower relative cumulative yields, canopy volumes, total soluble solids content, titratable acids, and seed content, but higher tree decline than `Lisbon' cultivars. Overall, `Foothill Lisbon', in spite of carrying exocortis viroid, produced good yields and fruit quality and `Prior Lisbon' had a satisfactory growth-performance.
`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.