14 research outputs found

    Citrus Genomics

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    Citrus is one of the most widespread fruit crops globally, with great economic and health value. It is among the most difficult plants to improve through traditional breeding approaches. Currently, there is risk of devastation by diseases threatening to limit production and future availability to the human population. As technologies rapidly advance in genomic science, they are quickly adapted to address the biological challenges of the citrus plant system and the world's industries. The historical developments of linkage mapping, markers and breeding, EST projects, physical mapping, an international citrus genome sequencing project, and critical functional analysis are described. Despite the challenges of working with citrus, there has been substantial progress. Citrus researchers engaged in international collaborations provide optimism about future productivity and contributions to the benefit of citrus industries worldwide and to the human population who can rely on future widespread availability of this health-promoting and aesthetically pleasing fruit crop

    Consumer Preferences for Fresh Citrus: Impacts of Demographic and Behavioral Characteristics

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    Fresh citrus, consumer preference, attitude, cluster analysis, market segmentation, Consumer/Household Economics, Crop Production/Industries, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety, Marketing, Q13,

    Phloem Regeneration Is a Mechanism for Huanglongbing-Tolerance of “Bearss” Lemon and “LB8-9” Sugar Belle® Mandarin

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    Huanglongbing (HLB) is an extremely destructive and lethal disease of citrus worldwide, presumably caused by phloem-limited bacteria, Candidatus Liberibacter asiaticus (CLas). The widespread invasiveness of the HLB pathogen and lack of natural HLB-resistant citrus cultivars have underscored the need for identifying tolerant citrus genotypes to support the current citrus industry’s survival and potentially to lead to future natural HLB resistance. In this study, transverse sections of leaf lamina and midribs were examined with light and epifluorescence microscopy to determine anatomical characteristics that underlie HLB-tolerant mechanisms operating among “Bearss” lemon, “LB8-9” Sugar Belle® mandarin, and its sibling trees compared with HLB-sensitive “Valencia” sweet orange. The common anatomical aberrations observed in all CLas-infected varieties are as follows: phloem necrosis, hypertrophic phloem parenchyma cells, phloem plugging with abundant callose depositions, phloem collapse with cell wall distortion and thickening, excessive starch accumulation, and sometimes even cambium degeneration. Anatomical distribution of starch accumulation even extended to tracheid elements. Although there were physical, morphological, and pathological similarities in the examined foliage, internal structural preservation in “Bearss” lemon and “LB8-9” Sugar Belle® mandarin was superior compared with HLB-sensitive “Valencia” sweet orange and siblings of “LB8-9” Sugar Belle® mandarin. Intriguingly, there was substantial phloem regeneration in the tolerant types that may compensate for the dysfunctional phloem, in comparison with the sensitive selections. The lower levels of phloem disruption, together with greater phloem regeneration, are two key elements that contribute to HLB tolerance in diverse citrus cultivars

    Plant mitochondrial introns as genetic markers - conservation and variation

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    Plant genomes are comprised of nuclear, plastid and mitochondrial components characterized by different patterns of inheritance and evolution. Genetic markers from the three genomes provide complementary tools for investigations of inheritance, genetic relationships and phenotypic contributions. Plant mitochondrial genomes are challenging for universal marker development because they are highly variable in terms of size, gene order and intergenic sequences and highly conserved with respect to protein-coding sequences. PCR amplification of introns with primers that anneal to conserved, flanking exons is effective for the development of polymorphic nuclear genome markers. The potential for plant mitochondrial intron polymorphisms to distinguish between congeneric species or intraspecific varieties has not been systematically investigated and is possibly constrained by requirements for intron secondary structure and interactions with co-evolved organelle intron splicing factors. To explore the potential for broadly applicable plant mitochondrial intron markers, PCR primer sets based upon conserved sequences flanking 11 introns common to seven angiosperm species were tested across a range of plant orders. PCR-amplified introns were screened for indel polymorphisms among a group of cross-compatible Citrus species and relatives; two Raphanus sativus mitotypes; representatives of the two Phaseolus vulgaris gene pools; and congeneric pairs of Cynodon, Cenchrus, Solanum, and Vaccinium species. All introns were successfully amplified from each plant entry. Length polymorphisms distinguishable by gel electrophoresis were common among genera but infrequent within genera. Sequencing of three introns amplified from 16 entries identified additional short indel polymorphisms and nucleotide substitutions that separated Citrus, Cynodon, Cenchrus and Vaccinium congeners, but failed to distinguish Solanum congeners or representatives of the Phaseolus vulgaris major gene pools. The ability of primer sets to amplify a wider range of plant species’ introns and the presence of intron polymorphisms that distinguish congeners was confirmed by in silico analysis. While mitochondrial intron variation is limited in comparison to nuclear introns, these exon-based primer sets provide robust tools for the amplification of mitochondrial introns across a wide range of plant species wherein useful polymorphisms can be identified

    Mining of haplotype-based expressed sequence tag single nucleotide polymorphisms in citrus

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    BACKGROUND: Single nucleotide polymorphisms (SNPs), the most abundant variations in a genome, have been widely used in various studies. Detection and characterization of citrus haplotype-based expressed sequence tag (EST) SNPs will greatly facilitate further utilization of these gene-based resources. RESULTS: In this paper, haplotype-based SNPs were mined out of publicly available citrus expressed sequence tags (ESTs) from different citrus cultivars (genotypes) individually and collectively for comparison. There were a total of 567,297 ESTs belonging to 27 cultivars in varying numbers and consequentially yielding different numbers of haplotype-based quality SNPs. Sweet orange (SO) had the most (213,830) ESTs, generating 11,182 quality SNPs in 3,327 out of 4,228 usable contigs. Summed from all the individually mining results, a total of 25,417 quality SNPs were discovered – 15,010 (59.1%) were transitions (AG and CT), 9,114 (35.9%) were transversions (AC, GT, CG, and AT), and 1,293 (5.0%) were insertion/deletions (indels). A vast majority of SNP-containing contigs consisted of only 2 haplotypes, as expected, but the percentages of 2 haplotype contigs varied widely in these citrus cultivars. BLAST of the 25,417 25-mer SNP oligos to the Clementine reference genome scaffolds revealed 2,947 SNPs had “no hits found”, 19,943 had 1 unique hit / alignment, 1,571 had one hit and 2+ alignments per hit, and 956 had 2+ hits and 1+ alignment per hit. Of the total 24,293 scaffold hits, 23,955 (98.6%) were on the main scaffolds 1 to 9, and only 338 were on 87 minor scaffolds. Most alignments had 100% (25/25) or 96% (24/25) nucleotide identities, accounting for 93% of all the alignments. Considering almost all the nucleotide discrepancies in the 24/25 alignments were at the SNP sites, it served well as in silico validation of these SNPs, in addition to and consistent with the rate (81%) validated by sequencing and SNaPshot assay. CONCLUSIONS: High-quality EST-SNPs from different citrus genotypes were detected, and compared to estimate the heterozygosity of each genome. All the SNP oligo sequences were aligned with the Clementine citrus genome to determine their distribution and uniqueness and for in silico validation, in addition to SNaPshot and sequencing validation of selected SNPs

    Consumer Preferences for Fresh Citrus: Impacts of Demographic and Behavioral Characteristics

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    In the last twenty years, trends within fresh fruit consumption have shifted from consumption of fresh citrus to non-citrus fresh fruit. Within citrus, consumers are switching from the traditionally dominant fruit, oranges, to tangerines. Using survey results from three cities in the U.S. on consumer preferences for fresh citrus products, we demonstrate that freshness, flavor and appearance are the most important attributes of fresh citrus. Heterogeneous preferences exist among consumers and both demographic and behavioral variables have significant impacts on preferences. Results indicate there are no dominant best predictors of consumer preferences. However, it appears there is potential to develop specific marketing strategies based on demographics

    Genome-Wide Association Study of Healthful Flavonoids among Diverse Mandarin Accessions

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    Mandarins have many unique flavonoids with documented health benefits and that help to prevent chronic human diseases. Flavonoids are difficult to measure and cannot be phenotyped without the use of specialized equipment; consequently, citrus breeders have not used flavonoid contents as selection criteria to develop cultivars with increased benefits for human health or increased tolerance to diseases. In this study, peel, pulp, and seed samples collected from many mandarin accessions and their hybrids were analyzed for the presence of selected flavonoids with documented human health benefits. A genome-wide association study (GWAS) was used to identify SNPs associated with biosynthesis of flavonoids in these mandarin accessions, and there were 420 significant SNPs were found to be associated with 28 compounds in peel, pulp, or seed samples. Four candidate genes involved in flavonoid biosynthesis were identified by enrichment analysis. SNPs that were found to be associated with compounds in pulp samples have the potential to be used as markers to select mandarins with improved phytonutrient content to benefit human health. Mandarin cultivars bred with increased flavonoid content may provide value to growers and consumers

    Surface barriers of mandarin 'okitsu' leaves make a major contribution to canker disease resistance

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    This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2014.[EN] Field evaluations have shown that Satsuma mandarin (Citrus unshiu) ‘Okitsu’ is one of the mandarin cultivars that shows substantial resistance to Xanthomonas citri subsp. citri (X. citri), the causal agent of citrus bacterial canker disease. However, the mechanisms underlying this resistance are not well understood. In this study, we have shown that ‘Okitsu’ leaves are nevertheless susceptible to X. citri infection during a period of their development; however, this period is shorter than that seen in the susceptible mandarin ‘Clemenules’ (C. clementina). Under controlled growth conditions, the resistance of ‘Okitsu’ to X. citri was associated with the age of the leaf and was evident in spray-inoculated plants but not in those inoculated by infiltration. Furthermore, X. citri showed reduced attachment and biofilm formation in ‘Okitsu’ leaves compared with ‘Clemenules’. Taken together, our data suggest that structural features of the ‘Okitsu’ leaf surface, such as the physical properties of the cuticle, are involved in the resistance to X. citri.This work was principally supported by the Agencia Nacional de Promocion Cientifica y Tecnologica PICT-2011-1833 to M. R. Marano and by a grant from the Florida Citrus Research and Development Foundation to F. G. Gmitter, Jr. and M. R. Marano. M. A. Chiesa, A. A. Vojnov, A. P. Castagnaro, and M. R. Marano are Career Investigators of CONICET. We thank R Vena for his technical assistance with the confocal microscopy and J. M. Dow and G. Gudesblat for critical review of the manuscript.Favaro, MA.; Micheloud, NG.; Roeschlin, RA.; Chiesa, MA.; Castagnaro, AP.; Vojnov, AV.; Gmitter, FGJ.... (2014). Surface barriers of mandarin 'okitsu' leaves make a major contribution to canker disease resistance. Phytopathology. 194(9):970-976. https://doi.org/10.1094/PHYTO-10-13-0277-RS970976194

    Metabolic Profiling of Hybrids Generated from Pummelo and Citrus latipes in Relation to Their Attraction to Diaphorina citri, the Vector of Huanglongbing

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    The citrus industry at present is severely affected by huanglongbing disease (HLB). HLB is caused by the supposed bacterial pathogen “Candidatus Liberibacter asiaticus” and is transmitted by the insect vector, the Asian citrus psyllid, Diaphorina citri Kuwayama. Developing new citrus hybrids to improve HLB management is much needed. In this study, we investigated the metabolomic profiles of three new hybrids produced from the cross of C2-5-12 Pummelo (Citrus maxima (L.) Osbeck) × pollen from Citrus latipes. The hybrids were selected based on leaf morphology and seedling vigor. The selected hybrids exhibited compact and upright tree architecture as seen in C. latipes. Hybrids were verified by simple sequence repeat markers, and were subjected to metabolomic analysis using gas chromatography-mass spectrometry. The volatile organic compounds (VOCs) and polar metabolites profiling also showed that the new hybrids were different from their parents. Interestingly, the levels of stored VOCs in hybrid II were higher than those observed in its parents and other hybrids. The level of most VOCs released by hybrid II was also higher than that released from its parents. Additionally, the preference assay showed that hybrid II was more attractive to D. citri than its parents and other hybrids. The leaf morphology, compact and upright architecture of hybrid II, and its attraction to D. citri suggest that it could be used as a windbreak and trap tree for D. citri (double duty), once its tolerance to HLB disease is confirmed. Our results showed that metabolomic analysis could be successfully used to understand the biochemical mechanisms controlling the interaction of D. citri with its host plants

    Cytological and molecular characterization of three gametoclones of Citrus clementina

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    Background: Three gametoclonal plants of Citrus clementina Hort. ex Tan., cv. Nules, designated ESP, FRA, and ITA (derived from three labs in Spain, France, and Italy, respectively), were selected for cytological and molecular characterization in order to elucidate genomic rearrangements provoked by haploidization. The study included comparisons of their ploidy, homozygosity, genome integrity, and gene dosage, using chromosome counting, flow cytometry, SSR marker genotyping, and array-Comparative Genomic Hybridization (array-CGH). Results: Chromosome counting and flow cytometry revealed that ESP and FRA were haploid, but ITA was tri-haploid. Homozygous patterns, represented by a single peak (allele), were observed among the three plants at almost all SSR loci distributed across the entire diploid donor genome. Those few loci with extra peaks visualized as output from automated sequencing runs, generally low or ambiguous, might result from amplicons of paralogous members at the locus, non-specific sites, or unexpected recombinant alleles. No new alleles were found, suggesting the genomes remained stable and intact during gametogenesis and regeneration. The integrity of the haploid genome also was supported by array-CGH studies, in which genomic profiles were comparable to the diploid control. Conclusions: The presence of few gene hybridization abnormalities, corroborated by gene dosage measurements, were hypothetically due to the segregation of hemizygous alleles and minor genomic rearrangements occurring during the haploidization procedure. In conclusion, these plants that are valuable genetic and breeding materials contain completely homozygous and essentially intact genomes
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