Citrus has an extended juvenile phase and trees can take 2-20 years to transition to the adult reproductive phase and produce fruit. For citrus variety development this substantially prolongs the time before adult traits, such as fruit yield and quality, can be evaluated. Methods to transform tissue from mature citrus trees would shorten the evaluation period via the direct production of adult phase transgenic citrus trees.
Cultivated citrus are selections from, or hybrids of, wild progenitor species whose identities and contributions to citrus domestication remain controversial. Here we sequence and compare citrus genomes-a high-quality reference haploid clementine genome and mandarin, pummelo, sweet-orange and sour-orange genomes-and show that cultivated types derive from two progenitor species. Although cultivated pummelos represent selections from one progenitor species, Citrus maxima, cultivated mandarins are introgressions of C. maxima into the ancestral mandarin species Citrus reticulata. The most widely cultivated citrus, sweet orange, is the offspring of previously admixed individuals, but sour orange is an F1 hybrid of pure C. maxima and C. reticulata parents, thus implying that wild mandarins were part of the early breeding germplasm. A Chinese wild ‘mandarin’ diverges substantially from C. reticulata, thus suggesting the possibility of other unrecognized wild citrus species. Understanding citrus phylogeny through genome analysis clarifies taxonomic relationships and facilitates sequence-directed genetic improvement.
Leprosis is one of the most serious citrus plant diseases. Leprosis-affected plants, especially sweet orange [Citrus sinensis (L.) Osbeck], which is the most widely cultivated citrus fruit worldwide, show reduced photosynthetic capacity and severe defoliation. The aim was to evaluate the relationship between the Brevipalpus phoenicis (Geijskes) vector mite and citrus leprosis disease in Pera sweet orange plants grafted on different rootstocks. Data were analysed using numerical classification and conventional statistical analysis (ANOVA).
Choisya ternata Kunth (Rutaceae) is a plant species used in Mexican folk medicine for its antispasmodic and simulative properties. Recently, we identified a new alkaloid, isopropyl N-methylanthranilate, and a related one, methyl N-methylanthranilate, from the essential oil of this species and have proven them to possess antinociceptive activity even at 0.3 mg/kg. In the present study, anxiolytic and antidepressant effects of the two compounds have been studied in open field, horizontal wire, light/dark, forced swimming and tail suspension tests, as well as the effect on the onset and duration of diazepam-induced sleep in BALB/c mice. The volatile alkaloids (50-200 mg/kg, administered intraperitoneally), without having a muscle relaxant effect, caused a significant increase in the time the animals spent in an unsecured and putatively dangerous area when compared with the control group but had no effect on the number of crossings between the light/dark compartments. In addition to this anxiolytic activity, a significantly antidepressant-like effect was apparent at all tested doses, which was not due to an increase in locomotive activity. The anthranilates administered on their own did not induce sleep in mice but significantly prolonged the diazepam-induced sleep, in a dose-dependent way, suggesting an interaction with the gamma-aminobutyric acid receptor complex. Copyright © 2012 John Wiley & Sons, Ltd.
Citrus tristeza virus (CTV) is phloem-restricted in natural citrus hosts. The 23 kDa protein (p23) encoded by the virus is an RNA silencing suppressor and a pathogenicity determinant. Expression of p23, or its N-terminal 157 amino acid fragment comprising the zinc-finger and flanking basic motifs, driven by the constitutive 35S promoter of cauliflower mosaic virus incites CTV-like symptoms and other aberrations in transgenic citrus. To better define the role of p23 in CTV pathogenesis, we compared the phenotypes of Mexican limes transformed with p23-derived transgenes from the severe T36 or the mild T317 CTV isolates under the control of the phloem-specific promoter from commelina yellow mottle virus (CoYMV) or the 35S promoter. Expression of the constructs restricted to the phloem incited a phenotype resembling CTV-specific symptoms (vein clearing and necrosis, and stem pitting), but not the non-specific aberrations (like mature leaf epinasty and yellow pinpoints, growth cease and apical necrosis) observed when p23 was ectopically expressed. Furthermore, vein necrosis and stem pitting in Mexican lime appeared specifically associated with p23 from T36. Phloem-specific accumulation of the p23Δ158-209(T36) fragment was sufficient to incite the same anomalies, indicating that the region comprising the N-terminal 157 amino acids of p23 is responsible (at least in part) for the vein clearing, stem pitting and possibly vein corking in this host.
Mandarin orange (MO) is an important fruit crop of tropical and subtropical regions of the world. A total of 217 morphologically distinct rhizobacteria from MO orchards in 3 states of northeastern India were isolated and analyzed for 4 plant-growth-promoting (PGP) attributes: nitrogen fixation, production of indole acetic acid like substances, solubilization of phosphate, and ability to antagonize pathogenic fungi. Isolates were ranked based on in-vitro-assayed PGP attributes, and 10 superior isolates were selected to test their effect on seedling emergence and seedling growth in a completely randomized pot experiment. These 10 isolates increased seedling emergence over a noninoculated control within 45 days after sowing. Five isolates, namely RCE1, RCE2, RCE3, RCE5, and RCE7, significantly increased shoot length, shoot dry biomass, and root dry biomass of 120-day-old seedlings over the noninoculated control. The beneficial effects of 4 selected strains, namely Enterobacter hormaechei RCE-1, Enterobacter asburiae RCE-2, Enterobacter ludwigii RCE-5, and Klebsiella pneumoniae RCE-7, on growth of the seedlings were visible up to 1 year after their transfer to 8 kg capacity pots. These strains were superior both in terms of in-vitro-assayed PGP attributes and of their beneficial effect in low phosphorus soil and, thus, may be promising bioinoculants for promoting early emergence and growth of MO seedlings.
Although studies have quantified bacterial transfer between hands and various materials, cross-contamination between the surface of fresh citrus fruit and the edible portions during hand peeling has not been reported. This study quantifies transfer of Salmonella to the edible portion of citrus fruit from a contaminated peel during hand peeling. Citrus fruits used for this study were Citrus sinensis (sweet orange) cultivars ‘Valencia’ and ‘Navel’, Citrus unshiu (Satsuma mandarins), Citrus reticulata × Citrus paradisi (‘Minneola’ tangelo or ‘Honeybell’), and C. paradisi (grapefruit) cultivar ‘Marsh’. An avirulent Salmonella Typhimurium LT2 (ATCC 700720) resistant to rifampin was used for all experiments. The inoculum containing approximately 9 log CFU/mL (50 μL) was spot inoculated onto the equator, stem, or styler of each fruit and allowed to dry for 24 h. Six volunteers put on single-use latex gloves and peeled inoculated fruit. Peel, edible fruit portion, and gloves were collected and enumerated separately. Three replicates of the study were performed in which each volunteer peeled two inoculated fruit of each variety (n = 36 fruit per variety). Cross-contamination from contaminated surface of citrus fruits to edible portion or gloved hands during peeling was affected by inoculation sites. Average Salmonella transfer to the edible portion ranged from 0.16% (Valencia inoculated at the equator) to 5.41% (navel inoculated at the stem). Average Salmonella transfer to gloved hands ranged from 0.41% (grapefruit inoculated at the stem) to 8.97% (navel inoculated at the stem). Most Salmonella remained on the peel of citrus fruits. The average level of Salmonella remaining on the peel ranged from 5.37% (Minneola inoculated at the equator) to 66.3% (Satsuma inoculated at the styler). When grapefruit was inoculated, the Salmonella that remained on the peel showed a bimodal pattern in which some individuals left almost all Salmonella on the peel, while others left substantially less.
The origin of limes and lemons has been a source of conflicting taxonomic opinions. Biochemical studies, numerical taxonomy and recent molecular studies suggested that cultivated Citrus species result from interspecific hybridization between four basic taxa (C. reticulata, C. maxima, C. medica and C. micrantha). However, the origin of most lemons and limes remains controversial or unknown. The aim of this study was to perform extended analyses of the diversity, genetic structure and origin of limes and lemons.
The chemical composition of volatile oils from 22 genotypes of Citrus and related genera was poorly differentiated, but chemometric techniques have clarified the relationships between the 22 genotypes, and allowed us to understand their resistance to D. citri. The most convincing similarities include the synthesis of (Z)-β-ocimene and (E)-caryophyllene for all 11 genotypes of group A. Genotypes of group B are not uniformly characterized by essential oil compounds. When stimulated with odor sources of 22 genotypes in a Y-tube olfactometer D. citri preferentially entered the arm containing the volatile oils of Murraya paniculata, confirming orange jasmine as its best host. C. reticulata × C. sinensis was the least preferred genotype, and is characterized by the presence of phytol, (Z)-β-ocimene, and β-elemene, which were not found in the most preferred genotype. We speculate that these three compounds may act as a repellent, making these oils less attractive to D. citri.
Three essential oils (EOs) were isolated from the peel of citrus fruits Citrus reticulata L., Citrus reticulata chinase Blanco and Citrus sinensis (L.) Osbeck (Family: Rutaceae) and evaluated against Culex pipiens L.1758 (Family: Culicidae). Chemical composition indicated that the EOs were rich in essential phytochemicals including hydrocarbons, monoterpenes and sesquiterpenes. These constituents revealed some variability among the oils displaying interesting chemotypes limonene (35-51%), 1R-α-pinene (1.04-2.5%), γ-terpinene (0.46-5.65%) and sabinene (0.51-5.42%). The toxicity proved that C. sinensis oil had more effect than C. reticulata chinase and C. reticulata oils against larvae (LC50 = 15.35, 16.11 and 32.84 mg/L, respectively). However, C. reticulate was the most active as fumigant against adults (LC50 2.74 μL/L air). The in vivo effect on acetylcholine esterase (AChE), carboxyl esterase (CbE), acid phosphatase (ACP), alkaline phosphatase (ALP), adenosine triphosphatase (ATPase) and glutathione-S-transferase (GST) were also demonstrated. To the best of our knowledge, this is the ﬁrst report about the chemical composition and mosquitocidal activity of C. reticulata chinase essential oils. Conclusively, the tested essential oils could be used as eco-friendly alternatives in mosquitoes control programme.