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.
Leaf chambers were placed on 6 leaves each of 3 trees of orange [Citrus sinensis (L.) Osbeck cv. Valencia] budded on rough lemon [Citrus limon (Lush) Burm. f.] rootstock, of which one tree was healthy and one in an early stage and one in an advanced stage of citrus blight, a decline disease of unknown etiology. Carbon dioxide exchange rates (CER) and leaf transpiration were measured every 7.5 minutes, continuously over a 2-week period. No difference in average leaf CER was observed among the 3 trees, but the decrease in leaf area associated with blight was confirmed. Leaf area index appeared not to have decreased sufficiently, even in the advanced-blight tree, to reduce light interception and thereby to reduce overall tree CER significantly.
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.
Studies with adenylate kinase (IUBN 184.108.40.206) activity in soluble and mitochondrial fractions from sweet lemon, Citrus limettioides, Tanaka, and sour lemon Citrus limon, L., were conducted. These species differ greatly in organic acid contents of fruits. These studies involved distribution, pH optimum, Mg++ requirement, inhibition of NaF, and equilibrium constant determination. The total adenylate kinase activity for the soluble and mitochondrial fractions was about 34% higher in extracts from sour lemons than in those from sweet lemons. The enzyme preparations from sweet lemons were more sensitive to inhibition by NaF than those from sour lemon. In both lemons, mitochondrial adenylate kinase activity was only 6–8% of the total adenylate kinase activity. Enzymatic breakdown of AMP to adenosine was higher in the soluble fraction than in the mitochondrial fraction.
These studies involved the development of a method to measure the endogenous levels of adenosine nucleotides in sweet lemon, Citrus limettioides, Tanaka and sour lemon, Citrus limon, L. These species differ greatly in organic acid contents of fruits. The adenosine nucleotides were precipitated as Ba salts and separated on DEAE-Sephadex A-25 anion exchange columns. The determinations included a range of fruit sizes from very young, growing to rather large, maturing, fruits of both lemon species. A noteworthy difference was found in the total adenosine nucleotides of very young fruits, with the sour lemon fruits having almost twice as much as the sweet lemon fruits. The ratio or ATP/AMP was found to be consistently higher (~3X) in young sour lemon fruits than in sweet lemon fruits. The energy charge was calculated from the concentrations of the nucleotides and little or no difference between the two lemon species was observed.
Citrus leaves from plants supplied with low soil oxygen showed a decreased sum of protein amino acids, while the free amino acids sum increased. Leaves from Phytophthora spp. infested plants contained a higher free amino acids sum than uninfested. The orange leaves, Citrus sinensis L. Osbeck cv. Atwood navel, contained a higher sum of protein amino acids than lemon leaves, Citrus limon L. Burm. cv. Prior Lisbon, although both of these species were budded on sweet orange rootstock, Citrus sinensis L. Osbeck cv. Bessie. Leaves from the orange scion contained lower concn of glutamic acid, glycine, valine, isoleucine, and leucine, and higher aspartic acid and phenylalanine than the lemon leaves. The sum of the free amino acids in the orange leaves was higher than in lemon leaves. Significant interaction effects on free cystine, methionine, and tyrosine were caused by Phytophthora spp. infestation in the 2 species.
Release, localization, and concentration of essential oils in chilling-injured and noninjured lemon [Citrus limon (L.) Burm.] fruit were investigated to enhance understanding of how chilling injury (CI) occurs in lemon. CI in the form of moderate to severe pitting of the flavedo was initially apparent after 3 weeks at 1 °C, followed by a gradual increase in severity until termination of the experiment after 7 weeks at 1 °C. Curing the fruit at 15 °C for 1 week before cold treatment greatly reduced the severity of CI. Release from the fruit of d-limonene, a major component of essential oil in lemon, increased with increasing amounts of CI. The enhancement of d-limonene release, however, lagged behind the development of CI. Studies of the internal anatomy of the flavedo using confocal microscopy indicated that essential oils were abundantly present inside the oil gland and in oil bodies outside the gland. Chilling-injured flavedo exhibited no obvious disruption of either the oil glands or the oil bodies. Extraction and quantification of d-limonene from chilling-injured and noninjured flavedo indicated that similar amounts of oil were present in the tissue, regardless of injury. Damage to the flavedo after 3 weeks at 1 °C was noted in the form of flattened or collapsed cells between the top of the gland and the epidermis, whereas collapse of the oil gland only was observed in later stages of injury development.
‘Villa franca’ is the main lemon (Citrus limon) variety in Israel, also cultivated in several other citrus-growing countries. In winter, the fruit turns yellow naturally, but during the summer and autumn, it remains green on the tree and requires postharvest ethylene treatment to stimulate color change from green to yellow. However, ‘Villa franca’ lemons are very sensitive to ethylene, which enhances development of reddish/brown peel blemishes known as red blotch. In the present study, we provide three different methods for postharvest degreening of ‘Villa franca’ lemons without causing red blotch. First is a slow process, involving natural degreening during 4–5 weeks of storage at 13 °C without ethylene exposure. Second is a moderate “under-degreening” process, involving a short 48-hour exposure to ethylene followed by 2 weeks of storage at 13 °C. Third is a fast process involving degreening with ethylene for up to 4 days at a constant high conditioning temperature of 30 °C or a combination of 24 hours of ethylene treatment at 30 °C followed by additional 72 hours of exposure to ethylene at 25 °C. Overall, ‘Villa franca’ lemon growers, packers, and exporters may now choose to use any of these proposed degreening procedures, according to commercial needs and market demands.
Green lemons (Citrus limon (L.) Burm.) were imaged for chlorophyll fluorescence (CF) 30 minutes after immersion of the fruit into 55 °C water for 5 minutes to determine if CF could be used to identify areas of hot water-induced rind injury before the appearance of visible symptoms. Fluorescence was variable in intensity over the surface of the rind with defined areas of enhanced fluorescence being present that corresponded in shape and location with visible injury that later developed during 24 hours of storage. Images showing minimum fluorescence (F0) and maximal fluorescence (Fm) provided the best image contrast between injured and noninjured areas of the rind. Total F0 present in the image was closely correlated (r 2 = 0.87) with the area of rind injury present following storage. Holding the fruit under conditions of low humidity for 24 h before hot water treatment prevented both the formation of areas of enhanced fluorescence and the corresponding rind injury. Imaging of CF has potential as a means to identify areas of incipient rind injury in citrus to facilitate study of the causal mechanisms of postharvest rind disorders.