Abstract
Long-term storage of lemon [Citrus limon (L.) Burm] at 13°C for 3 months and longer resulted in a high incidence of rot. The remaining sound fruit became dry, overripe in color, and therefore unmarketable. Storage at < 10°C caused chilling injury, including internal membranosis, peel pitting, and changes in juice composition (4). Intermittent warming for 7 days at 13° following 21 days at 2° eliminated chilling injury development in ‘Eureka’ and ‘Villa franca’ lemon, limons could be kept in storage for 6 months or longer and retain their marketing quality without chilling injury (5). Herein are presented the results of 2 years of commercial use of long-term storage of lemons at suboptimal temperature with intermittent warming.
Abstract
Photosynthesis and transpiration rates of seedlings of 4 citrus rootstocks under flooded conditions were measured over a 10-day period. For all rootstocks photosynthesis and transpiration decreased, but photosynthesis decreased relatively less than transpiration. Stomatal closure is inferred to account in part for the reductions observed.
Flooding did not increase ethanol concentration in either tops or roots, suggesting that ethanol is not an end-product of. anaerobic respiration in citrus seedlings. Only in the neutral soil was rough lemon (Citrus limon L. Burm. f.) found to be more tolerant to short-term flooding than ‘Cleopatra’ mandarin (Citrus reticulata Blanco) and trifoliate orange (Poncirus trifoliata L. Raf.). Tolerance to flood injury was greater at a soil pH of 7 than 4.5.
Abstract
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.
Abstract
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.
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
Studies with adenylate kinase (IUBN 2.7.4.3) 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.
Abstract
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.
Some lemon [Citrus limon (L.) Burm. f.] cultivars present compatibility problems with commonly used citrus rootstocks. Therefore, assessing trueness-to-type of lemon mother trees is needed by growers. Morphological differentiation of lemon cultivars is not precise because they present high phenotypic plasticity. The objective of this paper is to contrast the discriminatory ability of several molecular marker systems for lemon. Three marker types were used: randomly amplified polymorphic DNA (RAPD), inter-simple sequence repeats (ISSR) and inter-retrotransposon amplified polymorphism (IRAP). The molecular variability found in C. limon is larger than that reported for C. clementina, another vegetatively propagated citrus species. This difference in variability content might be explained by differences in the distribution and age of both cultures. Similar to clementines, polymerase chain reaction (PCR) markers using primers anchored in copya-like retrotransposons resulted in a higher rate of polymorphisms (36.4%) than did primers of random sequence (27.3%) or those anchored at simple sequence repeats (0%), indicating a higher molecular variability at the locations where these retrotransposons inserted. Primers anchored in gypsy-like retroelements did not yield polymorphisms. Lemon cultivars from important groups such as `Eureka', `Fino', and `Verna' could be distinguished using all polymorphisms.
Growth of young lemon trees (Citrus limon Burm. f.) is extremely vigorous, and is characterized by the appearance of highly vigorous upright shoots that originate in the scaffold branches and trunk of the tree. While maturing, these shoots are considered to be in competition for photosynthates with smaller fruit in the spring and with mature fruit in the fall. During 1993 and 1994, we selectively removed these shoots 12, 6, 4, and 1 (1994 only) times per year, with the objective of increasing fruit size. Neither yield nor fruit quality was affected by the pruning treatments during 1993, but pruning trees 12 times per year increased fruit size by 30% compared to unpruned trees. In 1994, lemon trees pruned 4 times per year had 50% less cull fruit than unpruned trees, and 22% more fruit of size 140 or larger. However, >99% of the flowers and small fruit on trees pruned 4 times per year were aborted, compared with 95% abortion on the unpruned trees. Trees pruned 4 times per year also had 40% less yield compared with those that were unpruned.
‘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.