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A corn -shaped fruit
Fruit showing a sharp difference in size between the top and bottom portions thus resembling an acorn. In cross-section, the albedo is thicker at the stem end and thinner at the stylar end. Fruit on stubborn- or exocortis-infected trees will sometimes show this acorn-shaped appearance (see Figure 39)

Acquisition feeding
The feeding period during which the insect ingests sap containing the pathogen

Alkaline phosphatase
An enzyme which hydrolyses certain phosphate containing compounds under alkaline conditions; commonly obtained from calf intestine mucosa

Amorphous plugs
Microscopic inclusions found in the trunk xylem tissue of blight-affected trees. These inclusions are uniformly dense and without structure (see Figure 33).

A protein formed in blood serum in response to stimulation by an antigen. Antibodies are specific for their respective antigens, and antigens and antibodies are mutually attracted

The reaction or attraction formed when reaction antigens meet their corresponding antibodies or vice versa. This strong attraction is the basis of all immunodetection systems

A substance, often a virus or bacteria, which stimulates production of antibodies in an animal. Specifically, it is the corresponding molecule to the antibody in a serological test

The technique or process of making a picture revealing the presence of radioactive material, the film being laid directly on the object to be tested. This is frequently used for detection of radioactivity following hybridization, by exposing kilter paper to sensitive X-ray film

Bark graft
One of a number of types of grafts used in the transmission of graft-transmissible pathogens. A piece of bark is cut from the host scion or rootstock and grafted to an indicator plant (see Figures 135-137)

One of the B-vitamin complex. It is widely distributed in plant and animal tissue, is water soluble and binds strongly to a glycoprotein named avidin.
Biotin derivatives of deoxyribonucleotides are incorporated into probe DNA by nick translation (see Part III). After hybridization the biotin can then be detected using streptavidinfluorescein complexes. The streptavidin binds to the biotin by one of the strongest known biological interactions.The enzyme (usually peroxidase or alkaline phosphatase) is then reacted with its substrate which gives a coloured product; fluorescein is detected by fluorescence under light of certain wavelength

A compound to which a small vitamin, biotin, has been attached. Antibodies, enzymes and nucleic acids can be labelled with biotin

Biotinylated enzyme
An enzyme coupled chemically to biotin

Biotinylated probe
A DNA probe in which certain bases were modified by chemical coupling of biotin

Blind bud
Not a true bud, but a section cut from that portion of the stem between buds containing no "eye" and used primarily for graft inoculations (see Eye, and Figure 127)

Blister inoculum
Inoculum tissue for graft transmission of psorosis-B used primarily in cross-protection studies. The tissue contains the blisters associated with the severe "B" form of psorosis (see Figure 79a)

As a verb, this means to transfer DNA, RNA or protein to an immobilizing matrix such as DMB-paper, nitrocellulose or nylon membranes. As a noun, it usually refers to the autoradiograph produced during the Southern or Northern blotting procedure

BRL Hybri-dot
A commercially available kit for applying small volumes of extracts to a membrane for testing the presence of viruses or viroids by hybridization

Budgraft inoculation
A bud, blind bud or chip bud cut from a stem of the plant or tree to be indexed and grafted to an indicator plant or tree

Bud-union crease
A line, ridge or fold, usually discoloured as brown, yellowish-brown or reddish-brown, and formed at the bud-union. It is readily observed when the outer bark is removed (see Figures 56 and 102-104). Some bud-union creases are caused by pathogens and others by incompatibility of rootstocks and scions

As in a tree canopy. The outline or total area of a tree, indicating its size

Complementary DNA. The DNA complement of an RNA sequence. It is synthesized by the enzyme RNA-primed DNA polymerase or reverse transcriptase. The single-stranded DNA product of this enzyme (the reverse transcript) may be converted into the double-stranded form by DNA-primed DNA polymerase, and inserted into a suitable vector to make a cDNA clone. cDNA cloning is commonly used to achieve the expression of mammalian genes in bacteria or yeast

cDNA probe
A radioactive specific DNA sequence used to detect complementary sequences of RNA or DNA (see cDNA and Probe)

Certification programme
A programme developed by a country, state, university or research centre for ensuring that selected budwood distributed to the growers is free of graft-transmissible pathogens and the fruit true-to-type. These pathogen-free certified trees are usually registered, and budwood issued from these mother or foundation-block trees can be used to produce additional buds in an increase block for the development of certified trees

A fibrous, graded, cellulose powder sold by the Whatman Company

Cheesy bark
Enlarged, swollen and softened bark tissue which, when cut into with a knife, resembles cheese. This type of cheesy bark is usually associated with the presence of severe CTV

Chip bud
A piece of bark tissue used for graft inoculation. It is used when the bark of receptor indicator plants does not slip or open up to accept a bud or blind bud (see description in Part II under Grafting techniques, and also Figure 127)

The separation of mixtures of chemicals, compounds, proteins, macro-molecules etc. into their constituents or components by preferential adsorption by a solid such as a column of cellulose, or by filter paper or by gel

A budline derived from a single parent source by propagation from that source

The internal, central, soft white column-like axis of the citrus fruit

See cDNA. A nucleic acid sequence is said to be complementary to another if it is able to form a perfect hydrogen-bonded duplex with it, according to the Watson-Crick rules of base pairing. A viral genomic ssRNA is complementary to "negative sense" ssRNA from which it is transcribed

Conjugated molecule
The temporary or permanent union, fusion or binding of two substances. When used in ELISA, it is the combining of antibody and enzyme proteins to form an enzyme-labelled antibody conjugate. The enzyme can then be detected colorimetrically, and the colour produced will give a fairly precise picture of the amount of virus present

DEAE cellulose column
A plastic or glass tube open at the top and fitted with a stopcock on the bottom. It contains diethylaminoethyl cellulose

So to modify (a protein) by heat, acid, or alkali that it retains its primary structure but no longer has all its original properties

To remove and separate proteins from other macromolecules from samples to be tested by hybridization. This is normally achieved by phenol extraction or by treating with a protein digesting enzyme

A procedure using a membrane to separate various components in solution in accordance with their ability to pass through the membrane

Cutting of tissue into small segments using a sharp knife or razor-blade. In the ELISA technique, leaf or bark segments are diced or cut up prior to grinding

Deoxyribonucleic acid. Any of a class of nucleic acids that contain deoxyribose, found chiefly in the nucleus of cells, and that functions in the transference of genetic characteristics and in the synthesis of protein

DNA probe
A probe for detection of specific nucleic acid segments (see Probe)

A procedure which is used to determine the presence and concentration of a particular RNA or DNA species. Different concentrations of the non-radioactive nucleic acids are denatured and applied as a dot to nitrocellulose paper or other support matrix. This is then hybridized with the radioactive complementary probe under study. After autoradiography, the intensities of the radioactive images formed are quantified and compared to a series to determine the concentration of the non-radioactive molecule

Denaturing polyacrylamide gel electrophoresis. Electrophoresis in a gel formed from polyacrylamide in the presence of a chemical agent such as urea (8M) or heat. It functions to minimize the effects of secondary and tertiary structure of the molecule on electrophoretic mobility

The electrophoretic transfer of macromolecules (DNA, RNA or protein) from a gel in which they have been separated, to a support matrix such as a nitrocellulose or a charged nylon sheet. An alternative to the capillary transfer usually used in techniques such as Southern and Northern blotting

Electro-blot membrane
A solid charged medium on to which a molecule is fixed as a result of electrophoresis from a source medium. This can be nitrocellulose or a charged nylon matrix

Removal of adsorbed material from an adsorbent by use of an electric field: or, recovery of a charged molecular species by electrophoretic migration from a source medium such as a polyacrylamide gel to a liquid medium in which concentration of the species can be accomplished

Electrophoretic techniques
Techniques which separate components suspended in a fluid media or gel by the influence of an electric field

The movement of a charged molecule from one medium to a second by migration in an electric field

Enzyme linked immunosorbent assay. Two antibody preparations are commonly used in ELISA. The primary antibody binds the antigen which is itself bound by the second antibody. The second antibody is linked to any enzyme whose activity is easily monitored, i.e. by colour change. The extent of enzymatic reaction is then a quantitative indication of the amount of antigen trapped by the primary antibody

Removal by dissolving, such as the removal of adsorbed material from an adsorbent by solvents

A small protuberance or growth found on a leaf, induced by insect bites or caused by the vein-enation virus. Very distinct enations can be seen on the veins of leaves of Mexican lime infected with vein-enation virus (see Figure 98)

Enzyme-labelled antibody
See Conjugated molecule and ELISA

An increase or decrease in growth of the upper or lower leaf surface or vein which causes the leaf to bend downward. Mild leaf epinasty is shown in an exocortis-infected citron leaf in Figure 42d, and severe epinasty in leaves of citron in Figure 41 a

Ethidium bromide
An intercalating agent which allows the ready detection of double-stranded nucleic acid molecules in agarose gels. The nucleic acid/ ethidium bromide complex fluoresces brightly when exposed to ultraviolet (UV) light (ethidium bromide is highly carcinogenic)

Eye (of a bud)
The protruding meristematic portion of a bud which later enlarges and grows into a young shoot or flower

As in leaf flecking. Usually a lighter translucent spot or small patch on leaves. Flecking in young or mature leaves is symptomatic for a number of graft-transmissible pathogens but can also be induced by environmental conditions or by the inherent genetic make-up of the plant

The new, young and fresh growth of shoots and leaves

Foundation tree
In a certification programme, the foundation tree is the primary tree derived from budwood which has been specially selected, shoot-tip grafted and/or heat-treated, and which has been indexed and certified as virus-free and also true-to-type. It will become the primary source tree for all future progeny trees. A foundation tree can be synonymous with a mother tree or mother block tree

A gametic seedling is one which was formed by sexual union and derived from seed containing the chromosomes of both parents. This is in contrast to the nucellar seedling containing only the chromosomes from the mother tree (see Nucellar)

The inert matrix used for electrophoretic separation of nucleic acids or proteins. Agarose gels are used for separation of DNA; agarose or polyacrylamide for RNA, and polyacrylamide for proteins

In reference to the greening organism, gracilicute is a division in the order of bacteria comprising organisms having a Gram-negative, membranous cell wall containing peptidoglycan

The transmission of a virus or other pathogen(s) by grafting tissue from the suspect host to an indicator plant

Gravity infusion
Used for testing the water uptake within a tree for the diagnosis of blight. It is the flow of water from a burette or other container suspended from a branch. The water is permitted to flow into the tree by gravity via a rubber or plastic tube (see Figure 31)

The formation of stable duplexes between complementary nucleotide sequences via Watson-Crick base pairing. The efficiency of hybridization is a test of sequence similarity. DNA-DNA, DNA-RNA, RNA-RNA hybrids may be formed. An alternate use of the word comes from classical genetics, and particularly plant breeding. Here hybridization means the formation of a novel diploid organism either by normal sexual processes or protoplast fusion

An assay system which detects proteins using an antibody specific to that protein. A positive result is seen as a precipitate of an antibody protein complex. The antibody can be linked to a radioactive atom or to an enzyme which catalyses an easily monitored reaction (see ELISA)

A procedure whereby either the antigen or antibody molecules are bound to a proteinbinding substrate, such as cellulose nitrate, and then exposed to the complementary antigen or antibody. The antigen-antibody complex which forms on the membrane is detected by an appropriately labelled antibody

A procedure where antibody and/or antigen molecules are allowed to migrate through an inert medium. A visible precipitate forms at the zone where related antigen and antibody molecules meet in a suitable concentration and react

The result of detection of antigens, often within tissues, by use of an antibody to which a fluorescent material is attached

A blood serum protein which functions as an antibody, commonly, a gamma globulin

A material which can adsorb serologically active molecules (antigens or antibodies). Cellulose nitrate and some plastics, such as certain polystyrenes, are good immunosorbents. Adsorbed molecules typically retain serological functions

Inclusion bodies
Cytopathic intracellular structures referred to as inclusion bodies are found in virus-infected plants. They contain virus particles, other proteins or structures specific to the virus and/or formed as a result of virus infection

Any test which will consistently confirm the presence (or absence) of a transmissible pathogen, or identify a disease. The index test should be specific for the pathogen or disease

Indicator plant
A plant used to test or index for the presence of a transmissible pathogen. The inoculated indicator plant will usually show very specific symptoms, thus permitting the diagnosis of a particular disease

Infection feeding
In contrast to acquisition feeding where the pathogen is ingested by the insect, infection feeding is secondary or the follow-up feeding where the pathogen is injected into the host plant by the insect

The process of infecting an indicator plant, usually by graft, mechanical or vector transmission

Inoculum tissue
Tissue which contains the transmissible pathogen or pathogens

Insipid (taste)
A dull, flat, savourless taste when fruit of stubborn-infected trees are tasted. This insipid taste is helpful in diagnosing possible stubborn infection when associated with other diagnostic symptoms

Intermediate antibody
An antibody used in the second step of an indirect ELISA assay. The intermediate antibody reacts to the antigen bound to the plate but is not labelled. The intermediate antibody is detected by using another antibody which is labelled and is specific only for the intermediate antibody

Interveinal clearing (or flecking)
The development of a clearing, flecking or lighter colour between leaf veins is usually associated with the presence of the concave gum or psorosis pathogen (see Flecking and Figure 83b)

Inverse stem-pitting
A type of pitting usually associated with citrus tristeza virus reaction of sweet orange, mandarin or grapefruit scions on sour orange rootstock. When a small segment of the sour orange bark is removed just below the bud-union, it will show numerous small pits on the inner surface of the bark, with corresponding needle-like pegs on the opposite wood surface of the trunk

Invisible pathogen
This refers to graft-transmissible pathogens which are present in citrus trees but which induce little or no symptoms in these trees. However, when budwood from these symptomless carriers is propagated or inoculated into a susceptible citrus species, symptoms can occur on the susceptible host (see Symptomless carrier)

Leaf-disc graft
A graft using round discs cut from leaves with a paper punch. The discs are matched to holes punched into leaves of an indicator plant and secured using adhesive tape (see Figures 1321 34)

Leaf-piece graft
A graft using as inoculum a small section cut from a young leaf of the test plant to be indexed. The leaf piece is then inserted into the stem of a receptor indicator plant in the same manner as a bud-graft and secured with wrapping tape

The conversion of a nucleic acid that is normally circular into a linear form of the molecule. This is done by cutting the circular form at a single site

As in loading ELISA plates. In ELISA, it is the process of adding a given amount of sample, buffer or any substance to the wells of an ELISA plate or gel apparatus

Mechanical transmission
Transfer or transmission of graft-transmissible pathogens by means other than grafting and not involving vectors. This can be done by knife cut, razor slash, hand or cotton rubbing of sap on leaves using carborundum powder, or by any other non-grafting method

Molecular hybridization
See Hybridization

Molecular probe
See Probe

In reference to mycoplasma-like organisms. One of the four divisions of the kingdom Procaryotae characterized by having no cell wall or peptidoglycan

Monoclonal antibodies
An antibody preparation which contains only a single type of antibody molecule. Monoclonal antibodies are produced naturally by myeloma cells. A myeloma is a tumour of the immune system. A clone of cells producing any single antibody may be prepared by fusing normal lymphocyte cells with myeloma cells to produce a hybridoma

Mother trees or mother-block trees
Similar or synonymous with foundation or foundation-block trees (see Foundation tree)

Negative stain
An electron-dense solution used to provide contrast around virus particles viewed on a transmission electron microscope

Nick translation
A procedure to insert radioactive or other tagged bases in a DNA probe. It is a process whereby damaged dsDNA molecules are repaired with nucleotides, some of which are radioactive. It is a good way to repair a probe

Nitrocellulose membrane
(Cellulose nitrate) A nitrated derivative of cellulose which is made into membrane filters of defined porosity, e.g. 0.45 mm 0.22 mm. These filters have a variety of uses in molecular biology, particularly in nucleic acid hybridization experiments. In the Southern and Northern blotting procedures, DNA and RNA, respectively, are transferred from an agarose gel to a nitrocellulose filter. Some centrifuge tubes are made of nitrocellulose; they are readily punctured with a hypodermic needle, and are frequently used for sucrose gradient

Northern blot, Northern transfer
A procedure analagous to Southern transfer but, in this case, RNA not DNA is transferred or "blotted" from a gel to a suitable binding matrix such as a nitrocellulose sheet. Single-stranded RNA is separated according to size by electrophoresis through an agarose or polyacrylamide gel; the RNA is then blotted directly on to the support matrix with no denaturation. RNA fixed to the supporting matrix can then be hybridized with a radioactive single-stranded DNA or RNA probe

Nucellar (seedling)
Referring to citrus, it is the seedling formed from the nucellus tissue surrounding the embryo. Nucellar seedlings resemble the parent plant and are quite uniform. However, a nucellar seedling or tree derived from a nucellar seedling is not identical to the parent tree, and may have many characteristics which are different. The nucellar process was used primarily to bypass citrus pathogens, and in particular exocortis

Nucleic acid
A DNA or RNA molecule which can be single-stranded or double-stranded

Nucleotide sequence
(See Sequencing.) It is the order (or sequence) of alignment of nucleotides of nucleic acid molecules

Oak-leaf pattern. A translucent pattern similar to the outline of an oak leaf, and induced in leaves of indicator plants or trees infected with the concave-gum family of viruses, which include concave gum, impietratura and cristacortis (see Figures 83a, 89 and 95)

Polyacrylamide gel electrophoresis (see Polyacrylamide gels). A method for separating nucleic acid or protein molecules according to their molecular size. The molecules migrate through the inert gel matrix under the influence of an electric field. In the case of protein PAGE, detergents such as sodium dodecyl sulfate are often added to ensure that all molecules have uniform charge. Secondary structure can often lead to the anomalous migration of a molecule. It is common, therefore, to denature protein samples by boiling them prior to PAGE. In the case of nucleic acids, denaturing formamide, urea, or methyl mercuric hydroxide are often incorporated into the gel itself, which may also be run at a high temperature. PAGE is used to separate the products of DNA-sequencing reactions and the gels employed are highly denaturing since molecules differing in size by a single nucleotide must be resolved

The needle-like growths or pinpoint projections observed on the wood or bark. These may be symptomatic for certain diseases of citrus. Pegs usually have corresponding pits on the opposite bark or wood surface

Polysaccharide chains covalently cross l inked by peptide chains. The presence or absence of peptidoglycan in the cell walls of bacteria is used to distinguish gracilicute-like organisms (which contain peptidoglycans) from mycoplasma-like organisms (which have no peptidoglycans)

Plant laboratory
A sophisticated greenhouse designed and used primarily for indexing

Plate-trapped antigen
Antigen which is adsorbed directly on the ELISA plate without use of a trapping antibody. For example, virus particles can be trapped to the surface of ELISA plates from extracts of infected tissue added to the wells of the plate. Other proteins, however, are also adsorbed

Polyacrylamide gels
Often referred to, incorrectly, as acrylamide gels. These gels are made by cross-linking acrylamide with N,N'-methylene-bis-acrylamide. Polyacrylamide gels are used for the electrophoretic separation of proteins and also RNA molecules. DNA molecules usually have too high a molecular weight to migrate far in polyacrylamide. Polyacrylamide beads are also used as molecular sieves in gel chromatography and are marketed under the brand name "Nio-gel"

Polyclonal antiserum
Antiserum harvested from the blood of immunized animals. Polyclonal antisera contain a mixture of antibodies to the various antigenic molecules present in the material used to immunize the animal. In contrast, monoclonal antisera contain only a single antibody

The production of one or more embryos from one seed. Nucellar seed may produce a number of seedlings from a single seed and this is sometimes called polyembryonic. In a true sense, it should be called multiple-sprouted nucellar seedlings

Potting mix
A mixture of ingredients used as an artificial soil medium for container growth of plants

Primary leaves
The first emerging leaves from a germinating seed. These leaves may be the cotyledons or may differ in shape from the secondary leaves

A low-molecular-weight species which promotes a reaction, such as an oligonucleotide which binds to a template permitting a copy of the template to be further synthesized

As a noun, probe is a specific DNA or RNA sequence which has been radioactively labelled to a high specific activity. Probes are used to detect complementary sequences by hybridization techniques such as Southern or Northern blotting or colony hybridization. The verb to probe is to hybridize in order to detect a specific gene or transcript, e.g. "We probed our bank with labelled viral RNA to detect clones containing viral DNA sequences."

Probe denaturization
Treating the probe under conditions that will separate its nucleic acid strands and enable their subsequent hybridization with the target molecules to be tested

Probe labelling
A variety of procedures that permit the labelling of probes with detectable tags

Bacteria-like organisms in the kingdom Procaryotae that have no organized nucleus and are surrounded by a nuclear membrane. Recent taxonomic literature suggests four divisions in the kingdom according to the presence of peptidoglycan and the type of cell wall. Both the greening organism and Spiroplasma citri are procaryote organisms; one a gracilicute-like organism and the other a mollicute

Protein A
Aprotein with a high affinity for antibody gamma globulins

As protuberances found in the rind of an impietratura-infected fruit. These are raised bumps or blister-like emergences on the rind, and when cut they will usually show gum underneath. The surface of protuberances of impietratura-infected fruit is often a shade of colour different from the rest of the rind (see Figure 84)

In reference to leaves infected with infectious variegation virus. The surface of the leaves appears drawn together into wrinkles and irregular folds, with puffed areas

Radioactive probe
A nucleic acid that has been made radioactive by one of several techniques (e.g. nick translation) and is to be used to detect a complementary nucleic acid sequence

Recombinant plasmid
A bacterial plasmid DNA containing an insert of DNA from a non-related source, e.g. a plasmid containing an insert of viral cDNA. It is created by recombinant DNA technology

Restricted endonuclease
Enzymes which recognize and cut double-stranded DNA at specific sites determined by the sequence of bases at that site

Reverse transcription
The enzyme which accomplishes the enzyme synthesis of a copy DNA from an RNA template in the presence of a primer and nucleotide triphosphates under appropriate conditions

Rf (replicative form)
The intercellular form of viral nucleic acid which is active in replication, e.g. M 13 phase particles contain a single-stranded DNA circle while the Rf of the same molecule is double-stranded

Circular, ring-like translucent or yellow spots on leaves (Figure 78a) or round spots on fruit (Figure 73). Ringspot is also the name of a psorosis-like disease which induces these symptoms on citrus leaves and fruit

Resuspension medium (see TKM buffer)

Ribonucleic acid. The alternative reservoir of genetic information to DNA. Viruses have single-stranded or double-stranded RNA genomes. In organisms, RNA is transcribed from DNA and is essential for the expression of the genetic information contained within the DNA. RNA differs from DNA in having ribose instead of deoxyribose as the sugar moiety in its nucleotides, and in having uracil instead of thymine as one of its two pyrimidine bases. RNA, but not DNA, may be degraded by alkaline hydrolysis

As in leaf rugosity, meaning rough or wrinkled, with puffed areas on the upper side of the leaf (see Puckered)

Scaly bark
The term used for a condition of the bark in psorosis-infected sweet orange, grapefruit or mandarin scions or rootstocks. The bark is scaled and exfoliated (see Figures 72a and 72b)

Scaly butt
A term used in Australia indicating exfoliation or scaling of the bark of the trifoliate orange rootstock due to infection with the citrus exocortis viroid

Secondary leaves
In contrast to the primary leaves of a germinating seed, the secondary leaves are the permanent type of leaves with a fixed morphology. Many seedlings produce both primary and secondary leaves, but many have just one type

Seed abortion
A term used to describe a condition of seed found in stubborn-infected fruit. The seed is not truly aborted, but appears smaller and has a darker purple or brown colour (see Figure 24b)

Seedling index
Indexing for transmissible pathogens in citrus done primarily using seedlings of sensitive varieties

Seedling yellows
A yellowing and severe stunting of young inoculated seedlings of sour orange, lemon or grapefruit associated with infection by severe citrus tristeza virus isolates

The determination of the order of nucleotides in a DNA or RNA molecule, or that of amino-acids in a polypeptide chain

Sequencing gel
A long, polyacrylamide slab gel which has sufficient resolving power to separate single-stranded fragments of DNA or RNA which differ in length by only a single nucleotide. Electrophoresis is carried out at high voltage and with the gel in a vertical position. Urea is usually included in the gel mixture as a denaturing agent. This prevents internal base pairing within the single-stranded molecules and ensures that their relative speed of migration is solely dependent on their length

As in the shock symptoms of psorosis-A-infected seedlings. After a seedling is inoculated and cut back, the first growth of a young shoot may show withering and bending, with loss of leaves. Ultimately the young shoot will dry up and turn dark brown. This is the shock symptom of psorosis-A (see Figures 75a and 76)

Shoot tip grafting
A micro-grafting procedure. The meristematic growing tip (the meristem plus one to three leaf primordia) is excised by cutting the very young tip using the cutting edge of a razor-blade mounted in a special handle. This decapitated tip is then grafted to a very young seedling with the aid of a binocular microscope. The grafted plant is then grown in test-tubes usually in vitro and later transplanted or grafted to produce a shoot-tip grafted plant or tree

Side grafting
A method of inoculation which uses a piece of stem 4-5 mm thick and 3-4 cm long. A wedge cut is made at the end of this stem piece; a cut is then made into the seedling to be indexed and the wedge end is fitted into the cut portion of the stem. The side graft is then wrapped. This type of graft is preferred when indexing for stubborn and greening diseases (see Figure 138)

Side shoot
A lateral branch or shoot. The Mexican lime seedling normally produces many side or lateral branches compared with the sweet or sour orange seedling which produces few or none

Single leader
In reference to the training of the young growing stem of a seedling or budded plant, to grow as one shoot. This one shoot is usually secured or tied to a stake with plant ties (see Figures 47 and 48)

As in a polythene sleeve enclosing side grafts. A polythene bag has the bottom removed or cut out to resemble the open-ended cut sleeve of a shirt or coat. The sleeve is placed over a recently grafted plant and tied at the top and bottom to ensure a moist chamber for the side grafts

As in bark slipping. A condition where the bark readily separates from the wood of the plant to be grafted. The plant is said to be "slipping" during the budding operation when a cut is made into the bark and it readily separates or opens up from the wood of the stem

See Dot-blot

Southern blot, Southern transfer
A technique which combines the resolving power of agarose gel electrophoresis with the sensitivity of nucleic acid hybridization. DNA fragments separated in an agarose gel are denatured in situ and then blotted or transferred, usually by capillary action, from the gel to a nitrocellulose sheet, or other binding matrix placed directly on top of the gel. Single-stranded DNA binds to the nitrocellulose and is then available for hybridization with labelled P32 or by colour change, in the case of a biotinylated probe. A very sensitive and powerful technique, it is often described as "blotting"

A thin stick made of bamboo, wood or metal which is forced into the soil of a containergrown plant and used to support the growing plant. The plant is secured to the stake by affixing special plant ties (see Figure 48)

STE buffer
Sodium chloride, Tris and EDTA (see Part III). Used in purification of nucleic acids including dsRNA and viroids

A microbial protein which binds biotin. It is preferred to avidin because of its more specific binding (see Biotin). In molecular hybridization, streptavidin reacts specifically with the biotin molecules fixed on the probe

As in a rootstock stub. The short projecting portion of the stem which remains after the rootstock is severed from the growing scion. The stub is that small portion above the scion which should be trimmed flush with the scion at a later time

Stylar end
The bottom portion of a hanging fruit

The substance acted upon by an enzyme. Usually this substance contains a chemical which, when acted upon by an enzyme, will change colour and the colour can be easily seen and measured

Symptomless carrier
Refers to a tree or plant which contains a grafttransmissible pathogen but shows no symptoms. Examples of a symptomless carrier would be a sweet orange scion on a sour orange rootstock containing tatterleaf virus and/or the exocortis viroid (see Invisible pathogen)

The joint action of agents such as two viruses acting together and inducing a more intense symptom in an indicator plant than by either agent acting alone

TAE buffer
Tris, sodium acetate.3H2O and sodium EDTA

Ripped, torn or shredded in a non-uniform pattern. The irregular leaf pattern associated with tatterleaf virus suggests an irregularly torn leaf

The molecule which is acted upon or copied, as in the production of cDNA probes by reverse transcriptase

Template primer
See Primer and Template

Treatment of budwood or plants by heat to effectively eliminate internal pathogens

TKM buffer
A buffer with Tris, KCl and MgCl2

As in TME Tris buffer. Tris, MgCl2 and EDTA

Trapping antibodies
Antibodies used to coat the wells of ELISA plates (the first layer in sandwich assay procedures). Antibodies adsorbed to the solid surface of the plate trap related antigens from the sample extracts placed in the plate for testing

Rubbing or grinding, as with tissue ground with pestle and mortar

Undulating depressions
As in symptoms induced by the cachexia viroid on the trunks of susceptible varieties. The depressions are not deep and sharp but rather have soft bends and undulations (see Figure 44)

Vein corking
A thick, cork-like growth on leaf veins induced by severe isolates of CTV or by boron deficiency (see Figure 8)

A small molecular RNA, transmissible in plants, without an extracellular protein component or translation capacity and which can be pathogenic. It is composed of naked, single-stranded low-molecular RNA (MW 80 000-130 000) which utilizes only host components for its replication. They exist in solution as rod-like structures arranged in a series of short base-paired and non-base-paired regions

Viruses are macro-molecular transmissible agents capable of causing diseases in plants and animals. They are small enough to pass through a millipore filter of 0.2 microns. They have been considered to be either living organisms or simply a molecular complex of nucleic acids and proteins capable of multiplication in living cells. Viruses are characterized by a core of nucleic acids with a genome less than 3 x 108 daltons in weight surrounded by a protein coat which can induce formation of antibodies.

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