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.
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).
The curative and protective activity of sodium bicarbonate (SBC) at 1% alone or in combination with fludioxonil (FLU), thiabendazole (TBZ) or with FLU and TBZ together, between 50 and 600 mg/L, was on fruit of different citrus species and cultivars. Fruits were either artificially inoculated with a resistant (TBZ-r) or sensible (TBZ-s) strain of Penicilium digitatum or not inoculated and incubated at 20 °C and 90% RH for 7 days (incubated fruit) or stored at 1.5 °C for 21 d plus 7 d of simulate marketing conditions at 20 °C and 60% RH. The effectiveness of these treatments was related with treatment-induced changes of epicuticular wax morphology, the mode of distribution of SBC, TBZ and FLU on fruit surface, and FLU and TBZ fruit residue levels. SBC alone showed a weak activity against both strains of P. digitatum. Both TBZ and FLU were very effective at all rates used, and their activity markedly increased when combined together or with SBC, even at concentrations of 50-150 mg/L. Fruit treated with SBC either alone or in combination with TBZ or/and FLU increased weight loss, although no treatment damage was detected. Residue levels of TBZ generally increased when TBZ was combined with FLU and/or SBC, while those of FLU slightly increased only in treatment where FLU was combined with TBZ and SBC. Initial residues of TBZ and FLU when applied at 600 mg/L were around 2 and 1 mg/kg, respectively, several times below the lowest MRLs set by most important citrus producing countries. In treatments with SBC or SBC plus TBZ or FLU, SEM observation of fruit surface showed a smoothing of cuticular wax platelets' surface, while ESEM micrographs showed irregular spots of salt deposits of roundish to irregular shape. The apparently uneven distribution of SBC or SBC plus TBZ or FLU or SBC plus TBZ and FLU on fruit, might in part reduce the potential beneficial effects of SBC or of fungicides-SBC mixtures.
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.
Mandarin (C. reticulata), citron (C. medica) and pummelo (C. maxima) are important species of the genus Citrus and parents of the interspecific hybrids that constitute the most familiar commercial varieties of citrus: sweet orange, sour orange, clementine, lemon, lime and grapefruit. Citron produces anthocyanins in its young leaves and flowers, as do species in genera closely related to Citrus, but mandarins do not and pummelo varieties that produce anthocyanins have not been reported. We investigated the activity of the Ruby gene, which encodes a MYB transcription factor controlling anthocyanin biosynthesis, in different accessions of a range of Citrus species and in domesticated cultivars. A white mutant of lemon lacks functional alleles of Ruby, demonstrating that Ruby plays an essential role in anthocyanin production in Citrus. Almost all the natural variation in pigmentation by anthocyanins in Citrus species can be explained by differences in activity of the Ruby gene, caused by point mutations, deletions and insertions of transposable elements. Comparison of the allelic constitution of Ruby in different species and cultivars also helps to clarify many of the taxonomic relationships in different species of Citrus, confirms the derivation of commercial varieties during domestication, elucidates the relationships within the subgenus Papeda and allows a new genetic classification of mandarins.
In the present work, molecularly imprinted polymer (MIP) microspheres were packed in polypropylene hollow fiber (HF) segments for the micro solid-phase extraction and clean-up of thiabendazole (TBZ) in citrus samples. Experimental parameters affecting TBZ extraction were carefully optimized. Hollow fiber membrane was able to protect MIP beads from solid matrix allowing the extraction and clean-up without the inclusion of further filtration and/or centrifugation steps. Under optimum experimental conditions, recoveries for TBZ at 0.83 mg kg-1 concentration level ranged from 5.1 to 6.1%, depending upon the sample analyzed (orange or lemon peel samples), with relative standard deviations (RSDs) lower than 4%. The limits of detection were 0.004 mg kg-1 in orange and 0.009 mg kg-1 in lemon, low enough for the determination of TBZ according to European Union legislation.
Greasy spot of citrus, caused by Zasmidium citri-griseum (= Mycosphaerella citri), is widely distributed in the Caribbean Basin, inducing leaf spots, premature defoliation, and yield loss. Greasy spot-like symptoms were frequently observed in humid citrus-growing regions in Panama as well as in semi-arid areas in Spain, but disease aetiology was unknown. Citrus-growing areas in Panama and Spain were surveyed and isolates of Mycosphaerellaceae were obtained from citrus greasy spot lesions. A selection of isolates from Panama (n = 22) and Spain (n = 16) was assembled based on their geographical origin, citrus species, and affected tissue. The isolates were characterized based on multi-locus DNA (ITS and EF-1α) sequence analyses, morphology, growth at different temperatures, and independent pathogenicity tests on the citrus species most affected in each country. Reference isolates and sequences were also included in the analysis. Isolates from Panama were identified as Z. citri-griseum complex, and others from Spain attributed to Amycosphaerella africana. Isolates of the Z. citri-griseum complex had a significantly higher optimal growth temperature (26.8°C) than those of A. africana (19.3°C), which corresponded well with their actual biogeographical range. The isolates of the Z. citri-griseum complex from Panama induced typical greasy spot symptoms in ‘Valencia’ sweet orange plants and the inoculated fungi were reisolated. No symptoms were observed in plants of the ‘Ortanique’ tangor inoculated with A. africana. These results demonstrate the presence of citrus greasy spot, caused by Z. citri-griseum complex, in Panama whereas A. africana was associated with greasy spot-like symptoms in Spain.
Colletotrichum species associated with citrus fruits are fragmentarily known and it lacks accordingly accurate information on the diversity carried alongside the trade of these commodities from producer countries to Europe. In this study, we investigated the molecular phylogenetic diversity, colonisation, and prevalence of Colletotrichum isolated from asymptomatic and diseased tissues of nine citrus fruit species from 17 geographically diverse countries. Totally 454 isolates were morphoculturally characterised, and multilocus analyses (ACT, ApMat, CHS-1, GAPDH, ITS, TUB2) was performed on a subset of representative morphotype isolates. Results led to the identification of three previously known species (Colletotrichum gloeosporioides, Colletotrichum karstii, Colletotrichum siamense) and one novel lineage comprising endophytic isolates from Citrus maxima. Based on this lineage, Colletotrichum citri-maximae is described as a new species in the Colletotrichum gigasporum complex, and is characterised by a long deletion in the GAPDH sequence, a character shared with three of its phylogenetic sister taxa. Prevalence of Colletotrichum varied among citrus species and was greatest on Citrus sinensis fruits. C. gloeosporioides was the most common species followed by C. siamense. Except for the new species, all other isolated Colletotrichum spp. also colonise citrus leaves, but the overall diversity on fruits may be lower than that of leaves.
Flavonoids are widely distributed in plants and play important roles in many biological processes. Citrus fruits are rich dietary sources of flavonoids. However, there have been very few reports about the comprehensive metabolic profile and natural diversity of flavonoids in different tissues of various Citrus cultivars. In this study, based on the 7416 metabolic signals detected with non-targeted metabolomics approach, Principal Component Analysis revealed the flavedo has the largest differences from other tissues in metabolite levels; as many as 198 flavonoid signals were then detected in 62 Citrus germplasms from 5 species mainly cultivated worldwide, while 117 flavonoids were identified, including 39 polymethoxylated flavonoids (PMFs), 7 flavones, 10 C-O-glycosylflavonoids, 44 O-glycosylflavonoids, 10 C-glycosylflavonoids and 7 newly annotated O-glycosylpolymethoxylated flavonoids. Tissue-specific accumulations were observed: O-glycosylated flavonoids were abundant in all fruit tissues, while PMFs were accumulated preferentially in the flavedo. Among different species, mandarins had the highest levels of PMFs and O-glycosylpolymethoxylated flavonoids, followed by sweet oranges. Based on the flavonoid profiles, 62 germplasms could be clearly grouped into five distinct clusters via hierarchical clustering analysis, which were perfectly matched with their species, with sweet oranges and mandarins clustering closely and being further away from other three species.
Investigation of the chemical constituents from the fruits of Citrus medica L. var. sarcodactylis Swingle has led to the characterization of a new sesquiterpene 1 along with thirty-two known compounds. The structure of 1 was established on the basis of 2D NMR spectroscopic and mass spectrometric analyses, and the known compounds were identified by comparison of their physical and spectroscopic data with those reported in the literature. In addition, most of the isolated compounds were evaluated for the activity assayed by the in vitro inhibition of superoxide anion generation and elastase release by human neutrophils. The results showed that only 6,7-dimethoxycoumarin (5) exhibited significant inhibition of superoxide anion generation, with IC50 value of 3.8 ± 1.4 μM.