Appendix C
Glossary
α-proteobacteria: A class of proteobacteria that are gram-negative; included in this class are most genera of phototrophic bacteria and several genera of bacteria that metabolize chemical compounds containing only one carbon atom, bacteria that are symbionts of plants and animals, and a group of pathogens (the Rickettsiaceae).
Abaxial (leaf surface): The upper side of the leaf.
Acquisition: For circulative pathogens like Candidatus Liberibacter spp., passage of ingested pathogens through the gut epithelial cells into the insect vector hemocoel (the blood-filled cavity of arthropods).
Acyl-homoserine lactone (AHL): A class of signaling molecules that are involved in bacterial quorum sensing (see quorum sensing).
Adaxial (leaf surface): The lower side of the leaf.
Advanced citrus production systems: See advanced production systems.
Advanced production systems: Production systems aimed at bringing new citrus groves into commercially viable production quicker than in traditional plantings by employing open hydroponics or intensive fertigation, high planting density, and a suitable rootstock capable of developing a compact tree and an efficient root system in the fertigated soil zone.
Agrobacterium: A bacterium that causes crown gall disease in a variety of plant hosts by horizontal transfer of pathogen genes for expression in the host; also an important tool in molecular biology for genetic engineering.
Aminoglycoside antibiotics: Traditional gram-negative antibacterial therapeutic agents that inhibit protein synthesis.
Annotation (genome sequence): The process of determining the location of genes and coding regions in a genome and their functions.
Anthocyanin marker: A blue, violet, or red flavonoid pigment found in plants that has been found to be a suitable visible selectable marker for plant transformation.
Antimicrobial proteins (AMPs): Low-molecular-weight proteins having broad spectrum antimicrobial activity against bacteria, viruses, and fungi. Those larger than 100 amino acids are often lytic enzymes or nutrient-binding proteins, or contain sites that target specific microbial macromolecules.
Arabidopsis: A genus of small, flowering plants in the Brassicaceae family that is popular as a model organism in plant biology and genetics research because of its small genome and rapid life cycle.
Assembly (genome): Aligning and merging sequenced fragments of DNA so as to reconstruct the original complete sequence in proper order.
Attract-and-kill: A pest control approach or strategy that involves luring the insect (for example, with pheromones) and then killing it with an insecticide.
Aurantioideae: A taxonomic subfamily within the family Rutaceae, which contains the citrus.
Bacteriome: A specialized organ, found mainly in some insects, that hosts endosymbiotic bacteria.
Bacteriophage: A virus that parasitizes a bacterium by infecting it and reproducing inside it (see also phage).
β-lactam antibiotics: A class of broad-spectrum antibiotics, consisting of all antibiotic agents that contain a beta-lactam ring in their molecular structures. This includes penicillin derivatives (penams), cephalosporins (cephems), monobactams, and carbapenems.
Biofilm: A slimy film of microorganisms and extracellular polysaccharides that adheres to a surface; cells within a biofilm undergo phenotypic shifts in which large suites of genes are differentially regulated.
Bioinformatic: Related to the analysis of biological information using computers and statistical techniques.
Biomarker: A substance, chemical, or gene used as an indicator of disease or a biological state.
Biosensor: A device that uses a living organism or biological molecules, such as enzymes or antibodies, to detect the presence of chemicals.
Brassinosteroids: A class of polyhydroxylated steroidal phytohormones with structures similar to steroid hormones produced by animals. Brassinosteroids regulate a wide range of physiological processes, including plant growth, development, and immunity.
Brix: The sugar content of an aqueous solution.
Callose: A plant polysaccharide composed of glucose residues linked together through β-1,3-linkages secreted by an enzyme complex (callose synthase), resulting in the hardening or thickening of plant cell walls.
Candidatus: A modifier appended to the binomial taxonomic name of an organism that cannot be fully characterized because it cannot be maintained in artificial culture medium.
cDNA library: A combination of cloned cDNA (complementary DNA) fragments inserted into a collection of host cells, which together constitute some portion of the transcriptome of the organism and are stored as a “library.”
Chelate: To form a compound from an organic ligand and a central metal ion at two or more points; chelation often facilitates the uptake of nutrients or removal of toxic substances.
Chemical genetics: The technique of screening for small-molecule modulators.
Chemical genomics approach: The systematic screening of targeted chemical libraries of small molecules against individual drug target families with the ultimate goal of identification of novel drugs and drug targets.
Circulative transmission: Movement of a pathogen from the insect foregut to the mid- and hindgut, from which it is transported to the hemolymph and further to the salivary gland, from which it is released into the plant tissue during insect feeding.
Citrus canker: An economically damaging disease caused by the bacterium Xanthomonas axonopodis pv. citri; canker outbreaks have occurred periodically in Florida despite a 10-year effort to eradicate the disease from Florida. A series of legal challenges and an unprecedented rash of storms in 2004 and 2005 led to disease spread to a point in 2006 at which eradication was no longer considered possible.
Citrus Health Management Areas (CHMAs): Groupings of commercial citrus groves in close proximity where growers work cooperatively to manage the spread of HLB. The goal of CHMAs is to coordinate the timing and ensure the proper rotation of pesticide mode of action to obtain the best psyllid control possible while minimizing the potential for pesticide resistance development.
Citrus tristeza virus (CTV): An aphid-transmitted, phloem-residing Closterovirus that causes the most destructive disease of citrus in the Western Hemisphere and has a worldwide distribution; viral vectors based on modifications of the Citrus tristeza virus RNA are useful for transfecting citrus trees for beneficial purposes.
Clustered regularly interspersed short palindromic repeats (CRISPR): Segments of prokaryotic DNA containing short, repetitive base sequences occurring naturally as an acquired immune response system in bacteria and archaea; these have been adopted recently as a component of a gene-editing system (see gene editing).
Cofactor: A nonprotein chemical compound or metallic ion that is required for a protein’s biological activity to happen.
Cost–benefit ratio: An indicator, used in cost–benefit analysis, that attempts to summarize the overall value for money of a project or a proposed approach.
Defense marker gene(s): Markers that are associated with a plant response to pathogen infection.
Diapause: A period of suspended or arrested development during an insect’s life cycle.
Downregulation: The process by which a cell decreases the quantity of a cellular component, such as RNA or protein, in response to an external variable.
Ectopic: In an abnormal place or position.
Effector (bacterial): A protein such as an inducer, a corepressor, or an enzyme, secreted by pathogenic bacteria into host cells, that activates, controls, or inactivates a process or action; effectors usually help the pathogen to invade host tissue, suppress its immune system, or otherwise help the pathogen to survive, and are usually required for virulence.
Electrical penetration graph (EPG): A technology used to study the interactions of insects with plants through the creation of an electrical circuit by attaching a conductive wire to the insect and to the plant, with resulting signal patterns displayed as a waveform graph; often used to study the basis of plant pathogen transmission, host plant selection by insects, and the way insects can find and feed from the plant phloem.
Endosymbiont: An organism living symbiotically inside the cells or body of another organism.
Entomopathogen: Organisms capable of causing disease in insects.
Explant: Small piece of plant tissue that is aseptically cut and used to initiate a culture in a nutrient medium.
Fecundity: The ability to produce an abundance of offspring.
Fertigation: The injection of fertilizers, soil amendments, and other water-soluble products into an irrigation system.
Fitness: The ability of organisms to survive and reproduce in the environment in which they find themselves.
Flight mill: A device for measuring the speed, distance, and periodicity of insect flight.
Flush (citrus flush): New leaves produced simultaneously on all branches of a bare plant or tree; results in an abundance of young, tender leaf tissue to which citrus-feeding insects are attracted.
Gene editing: Unlike genetic engineering, this technology can be used to very precisely edit or change the genetic code of an organism’s own native genome at precise locations; nucleases are used to cut DNA at a specific location in the genome, and the cell’s DNA repair mechanisms can be directed to introduce, delete, or replace specific sections of the genetic code.
Genetic engineering: A technology that is employed to alter the genetic material of living cells by introducing foreign DNA (from the same or a different species, or even artificially synthesized DNA) so that they produce new substances or perform new functions; typically the location where the new DNA sequence inserts into the genome is random.
Glutathione-S-transferase: An enzyme catalyzing the conjugation of reduced glutathione to xenobiotic substrates, increasing their solubility, for the purpose of detoxification.
Graft: To unite a shoot or bud (i.e., scion) to an established plant (i.e., stock) by insertion or attachment, or the plant construct resulting from that union.
Graft inoculation: Method of inoculation often used for the initial establishment of infection of a nonmechanically transmissible pathogen, involving the grafting (see graft) of scions excised from symptomatic parts of the infected plant.
Gram-negative (bacteria): Characterized by cell envelopes composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. Named for a characteristic staining reaction.
Gustatory: Of or relating to taste or tasting.
Hemipteran: Any of various insects of the order Hemiptera, having biting or sucking mouthparts and two pairs of wings.
High-throughput: An approach or method that involves automation such that large-scale repetition becomes feasible.
Hybridization (citrus): The crossing of two individuals or plants or lines with dissimilar genotype, resulting in a hybrid.
Immunity: A condition of being able to resist a particular disease, especially through preventing development of a pathogenic microorganism or by counteracting the effects of its products.
Inoculation: For Ca. Liberibacter spp. it is the passage of pathogens in saliva from the salivary glands (of the insect vector) into phloem sieve elements via salivation.
Inoculative (insects): Infective insects that will transmit during a given test access period.
Inoculum: Biological material, cell, or part of a pathogen that induces disease.
Instar: A developmental stage of insects, between each molt, until sexual maturity is reached.
Integrated pest management (IPM): A strategy aimed at long-term prevention of pests or their damage by using a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties.
Intellectual property: Work or invention to which one has rights and for which one may apply for a patent, copyright, trademark, etc.
Juvenility: Plant growth stage during which a plant cannot be induced to flower.
Latent period (incubation period): In plants, the interval in the course of a disease between plant infection and the first appearance of the symptoms; in insects, the interval between pathogen acquisition and inoculativity.
Leucine-rich repeat (LRR): A protein composed of repeating 20– to 30–amino acid stretches that are unusually rich in the hydrophobic amino acid leucine; frequently involved in protein–protein interactions.
Loop-mediated isothermal amplification (LAMP): A technique for the amplification of DNA, which involves a reaction that takes place in a single tube containing buffer, target DNA, DNA polymerase, and primers.
LuxR: A protein (the transcriptional activator of luminescence) involved in quorum sensing (see quorum sensing) and intercellular communication in bacterial species.
Lysogenic (cycle): One of two cycles in bacterial virus reproduction, characterized by the integration of the bacteriophage nucleic acid into the host bacterium’s genome or formations of a circular replicon in the bacterial cytoplasm. See also lytic.
Lytic (cycle): One of two cycles in bacterial virus reproduction that results in the destruction of the infected cell and its membrane. See also lysogenic.
Master regulator: A gene at the top of a gene regulation hierarchy, particularly in regulatory pathways related to cell fate and differentiation.
Meta-analysis: An approach that assumes that there is a common truth behind all conceptually similar scientific studies, but which has been measured with a certain error within individual studies and uses statistical approaches to derive a pooled estimate closest to the unknown common truth.
Metabolomics: The study of the unique chemical fingerprints left by specific cellular processes, and of their small-molecule metabolite profiles.
Microbiome: The ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share an environmental niche such as a living organism.
Microfluidics: A multidisciplinary field producing systems in which low fluid volumes are processed to achieve multiplexing, automation, and high-throughput screening.
Miraculin: A glycoprotein extracted from Synsepalum dulcificum berries that can serve as a natural sugar substitute.
Mitogenome: The DNA located within mitochondria.
Morphotype: Any of a group of different individuals of the same species in a population, a morph.
Mutagenesis: A process by which the genetic information of an organism is changed in a stable manner, resulting in a mutation.
Nanoemulsion: An emulsion in which the disperse phase consists of nanosized particles.
Nanoparticle: A particle between 1 and 100 nanometers in size with a surrounding interfacial layer.
Neonicotinoid: A class of neuroactive insecticides chemically similar to nicotine.
Nucellar embryony: A form of seed reproduction in which embryos genetically identical to the parent plant develop from the nucellar tissue.
Nymph: An immature form of an insect that does not change greatly as it grows.
Olfactory receptor: A protein that binds odor molecules.
Olfactory receptor co-receptor (Orco): Odorant co-receptor that complexes with conventional odorant (olfactory) receptors to form odorant-sensing units.
Omics: A field of study in biology ending in -omics, such as genomics, proteomics, or metabolomics.
Ortholog: Any gene found in two or more species that can be traced to a common ancestor.
Oviposition: The process of laying eggs.
Parasitoid: An insect whose larvae live as parasites that eventually kill their hosts, typically other insects.
Pathogen-associated molecular patterns (PAMPs): Small molecular motifs associated with groups of pathogens, conserved within a class of microbes, that are recognized by cells of the innate immune system.
Phage: Shortened form of bacteriophage (see bacteriophage).
Phage therapy: Therapeutic use of bacteriophages to treat pathogenic bacterial infections.
Phagostimulant: A chemical that stimulates feeding.
Phenology: The study of cyclic and seasonal natural phenomena.
Phototaxis: The movement of an organism either toward or away from a source of light (adj: phototactic).
Phylogenetic: Relating to the evolutionary development and diversification of a species or group of organisms, or of a particular feature of an organism.
Phytobiome: Plants, their environment, and their associated communities of organisms.
Phytoplasmas: Cell wall–less prokaryotic parasites of plant phloem and of insect vectors involved in their transmission.
Plant growth regulator (PGR): A natural or synthetic chemical that alters plant growth or development, also referred to as plant hormones.
Polyembryonic: Forming multiple embryos from a single fertilized ovum or in a single seed.
Polymerase chain reaction (PCR): A molecular technique to amplify a single or a few copies of a segment of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence.
Probe: A fragment of DNA or RNA that can be labeled and used to detect the presence of nucleotide sequences that are complementary to the probe sequence.
Promoter: A region of a DNA molecule that forms the site at which transcription of a gene begins.
Propagative transmission: Pathogen transmission characterized by a long period of acquisition of the pathogen by a vector, a latent period before the vector is able to transmit the pathogen, and retention of the pathogen by the vector for a long period because the pathogen reproduces or replicates in the vector.
Prophage: The genetic material of a bacteriophage, incorporated into the genome of a bacterium and able to produce phages if specifically activated.
Protease: An enzyme that digests proteins and peptides.
Protein marking (of insects): The application of a distinctive and detectable marker protein to populations of insects such that they can later be detected by a method, such as enzyme-linked immunosorbent assay (ELISA), specific to the marker.
Proteome: The entire set of proteins expressed by a genome, cell, tissue, or organism at a given time, under defined conditions.
Quantitative PCR (qPCR): Also called real-time PCR, a polymerase chain reaction that monitors the amplification of a targeted DNA molecule during the PCR, i.e., in real time, and not at its end, as in conventional PCR.
Quorum sensing: A system of stimuli and response correlated to population density that enables bacteria to restrict the expression of specific genes to the high cell densities at which the resulting phenotypes will be most beneficial.
Reactive oxygen species (ROS): Chemically reactive compounds containing oxygen, formed as byproducts of the normal oxygen metabolism and having important roles in cell signaling and homeostasis.
Reflective mulch: Also called metallic mulch; mulching material containing metal that reflects sunlight, providing weed control, soil moisture retention, and soil warming, and repelling some insects.
Replanting (reset): Replacing individual diseased citrus trees one-by-one within mature groves.
Replanting (solid set): Planting new solid sets of seedlings across large areas following large acreage removals.
Reservoir (for pathogen or psyllid): A population of organisms or the specific environment (usually a susceptible host) in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival.
Resistance gene (R gene): A plant gene that conveys plant disease resistance against pathogens by producing resistance (R) proteins.
Resistant (to plant disease): Having a genetic makeup allowing prevention or reduction of pathogen growth on or in the plant, leading to the absence or reduction of disease.
Retention (vector transmission phase): After acquisition, the period of time during which the pathogen remains present and viable in the insect. For Ca. Liberibacter spp., it is the act of pathogen moving through the hemocoel infecting various organs, including the salivary glands.
Rhizoplane: The root surface.
RNA interference (RNAi): One type of small RNA, RNAi is a defense mechanism in plants, fungi, and animals against foreign double-stranded RNA, such as viruses; characterized by the prevention of messenger RNA (mRNA) translation by specialized protein complexes in the host.
Rootstock: In grafting of citrus, a plant stump having an established, healthy root system, onto which a cutting or a bud from another plant is grafted.
Rutaceae: A family of plants (“rutaceous”) including citrus and related species.
Salicylate hydroxylase: An enzyme that catalyzes the decarboxylative hydroxylation of salicylate to form catechol, a product that does not induce resistance. Salicylate hydroxylase (SahA) produced by Candidatus Liberibacter asiaticus (CLas) has been found to degrade salicylic acid and suppress plant defenses.
Salicylic acid: An important signal molecule in plant defense and signaling in plants.
Salivary sheath: An envelope surrounding the stylets of some phytophagous insects formed during stylet propagation inside the plant.
Scion: A young shoot or twig of a plant, especially one cut for grafting onto a rootstock during plant propagation.
Sclerenchyma: Strengthening tissue in a plant, formed from cells with thickened, typically lignified, walls.
Sec: A bacterial secretion system, conserved among a number of bacterial species, that translocates proteins, primarily in their unfolded state, across bacterial membranes.
Semiochemical: A chemical substance or mixture that carries a message for intraspecific or interspecific communication.
Sequencing (genome): A process that determines the complete DNA sequence of an organism’s genome at a single time.
Sieve tube: A collection of specialized phloem cells, connected end-to-end, forming a continuous tube through which organic solutes (and phloem-restricted pathogens, including some bacteria and viruses) are translocated.
Small RNA: RNA molecules <200 nt and usually noncoding; one example is RNAi, which is often involved in RNA silencing.
Source-sink: With respect to in-plant translocation, the movement of materials from a source (such as carbohydrates from areas of photosynthesis such as leaves) to other, nonphotosynthetic, tissues throughout the plant.
Sticky card (yellow sticky card): A trap consisting of a sticky glue layer mounted on a piece of cardboard, used to monitor and catch insects and other pests.
Stylet sheath: See salivary sheath.
Sulfonamide(s): A class of synthetic drugs, derived from sulfanilamide, that are able to prevent the multiplication of some pathogenic bacteria.
Susceptible (to plant disease): Having a genetic makeup that permits the development of a particular disease.
Systemic acquired resistance (SAR): A “whole-plant” resistance response that occurs following an earlier localized exposure to a pathogen, when plants use pattern-recognition receptors to recognize conserved microbial signatures.
Thermotherapy: The use of heat to eliminate or reduce numbers of a pathogen in a host plant without significant detriment to the plant.
Tolerant (to plant disease): Able to grow and produce a good crop or maintain an acceptable appearance even when infected with a plant pathogen.
Transcription: The first step of gene expression, in which a particular segment of DNA is copied into RNA (mRNA) by the enzyme RNA polymerase.
Transcriptional regulator: A chemical that stimulates or represses the process of transcription.
Transcriptome: The set of all messenger RNA molecules in one cell or a population of cells.
Transformation: The natural or laboratory genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous DNA from its surroundings through the cell membrane.
Transgene: A gene or genetic material that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another.
Transmission (pathogen): A process involving pathogen escape from the host, and travel to and infection of a new host.
Transpeptidase: An enzyme that catalyzes the transfer of an amino group from one peptide chain to another.
Upregulation: The process by which a cell increases the quantity of a cellular component, such as RNA or protein, in response to an external variable.
Vector: An agent, such as a plasmid or virus, used to carry DNA into a cell; an insect or other living entity that transmits a pathogen.
Vertical transmission: Transfer of an infectious agent from parent to offspring via transovarial transmission.
Virulence: Expression of the degree of damage caused to a host plant by infection with a particular pathogen, generally negatively correlated with host fitness.
Virulence factor: A molecule produced by a pathogen that enables it to colonize the host, evade or suppress the host’s immune response, obtain nutrition from the host, and/or enter or exit from host cells (if an intracellular pathogen).
Volatile organic compound (VOC): An organic substance easily evaporated at normal temperatures.
Windbreak: A row of trees or a fence, wall, or screen that provides shelter or protection from the wind.
Wing aspect ratio: The ratio of the span of a wing to its mean chord (length in the direction of wind travel over the wing); a high ratio describes a long, narrow wing, while a low ratio describes a short, wide wing.
Wolbachia: A genus of gram-negative bacteria that infects or lives endophytically within arthropods, often in complex relationships that may be parasitic, mutualistic, or beneficial.
