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... more 10.000 glossed keywords and links to more than 100 figures and schemes, about 100 tables etc. can be obtained in addition to this limited INTERNET version either on CD-ROM or in modified design as book by CRC Press, Taylor & Francis Group, Boca Raton, USA

Dalton (Da): a unit equal to the mass of the hydrogen atom (1.67 x 10 –24 g); the unit was named after J. DALTON, a chemist of nineteenth century chem

dam gene: DNA adenine methylation gene of Escherichia coli; it methylates the sequence GATC (Sau3A cleaves methylated and unmethylated DNA, MboI cleaves only unmethylated DNA, DpnI cleaves only the methylated sequence) biot

dammar resin: a hard, lustrous resin derived from Asian trees of the monkey-puzzle family prep

dandelion weeder >>> asparagus knife

dark-field >>> dark field microscopy

dark field microscopy: a microscope designed so that the entering center light rays are blacked out and the peripherical rays are directed against the object from the side; as the result the object being viewed appears bright upon a dark background micr

dark reaction: the phase of photosynthesis, not requiring light, in which carbohydrates are synthesized from carbon dioxide phys

dark respiration >>> dark reaction

dark room: a room in which film, photographic material, is handled or developed and from which the actinic rays of light are excluded prep; a dark room is also used in order to simulate short-day conditions; it is applied either to prevent flowering of long-day plants or to induce flowering of short-day plants under long-day conditions meth

DArT marker >>> diversity arrays technology (DArT) marker

Darwinism: the theory that the mechanism of biological evolution involves natural selection of adaptive variations bio

database: a store of a large amount of information (e.g., in a form that can be handled by a computer); recently, in breeding, numerous databanks are in use, such as field registration, nursery plans, selection data, data of international observation trials, statistical values, data recording, etc. stat

data management: the organization of the recording of data, its preparation for analysis and its interpretation prep

data sheet: a specially prepared form on paper or computer for recording data meth

dauermodification >>> persistent modification

daughter cell: the cells resulting from the division of a single cell cyto

daughter chromosome: any of the two chromatids of which the replicated chromosome consists after mitotic metaphase or anaphase II of meiosis cyto

daughter nucleus: the nuclei that result from the division of a single nucleus cyto

daylength: the number of hours of light in each 24-hour cycle phys

daylength insensitivity: these plants will flower independent of daylength (e.g., tomato or cotton) phys

daylength response >>> daylength sensitivity

daylength sensitivity: plants that will flower only when the daily photoperiod shows a critical length phys >>> short-day plants >>> long-day plant >>> day-neutral plants

day-neutral plants: no daylength requirement for floral initiation phys

debearder: in seed precleaning procedures, it has a hammering or flailing action that removes awns, beards, or lint from seed and tends to break up seed clusters of the chaffy grasses, as well as multiple seed units of nonchaffy forms seed >>> Table 11

decarboxylase: an enzyme that removes the carboxyl group from an organic compound chem phys

decay: the destruction of plant material by fungi and bacteria agr

deciduous: a plant whose leaves are shed at a season or growth stage, by abscission; the function of this habit is usually to escape an adverse season, such as a winter, or a tropical dry season; the deciduous habit also has advantages in the control of leaf parasites by providing a discontinuous pathosystem in which a gene-for-gene relationship can operate as a system of biochemical locking bot

decimal code for the growth of cereal plants: a decimal code used for describing different growth stages of cereal plants; it is applied for comparison of several morphological stages; there are several schemes of description phys meth >>> Table 13

declining vitality: seeds that are aged or have been subjected to unfavorable storage conditions; they usually show a slow germination; some of the essential plant parts are frequently stunted or lacking; saprophytic fungi may also interfere with the growth of the seedlings seed

decompose: to rot or putrefy agr

decomposer: an organism that breaks down dead tissues into simple chemical components, thereby returning nutrients to the physical environment of plants bio

decondensation stage: a stage between interphase and prophase of mitosis in which heterochromatin is decondensed for a short period cyto

decontaminate: to free from contamination; purify meth

decumbent: lying on the ground with the end ascending bot

decurrent: describes the open type of collar in barley where the margin of the platform is incomplete, merging with the neck; in general, extending downward from the point of insertion bot

dedifferentiation: a loss of specialization of a cell; it can be observed when differentiated cells are placed in vitro culture biot

deficiency: the absence or deletion of a segment of genetic material cyto >>> chromosome mutation

deficiency disease(s): disease caused by the lack or insufficiency of some nutrient, element, or compound (e.g., copper, zinc, or iron deficiency in cereals); deficiency diseases are among the nonparasitic physiological disorders, which are due mainly to nutritional deficiencies or toxicities; each nutritional element produces its own deficiency symptoms;within one plant, mobile elements can be taken from old tissues to feed the young tissues, and the symptoms then appear mainly in the older tissues; conversely, immobile elements cannot be re-allocated in this way, and the main deficiency symptoms then appear in the youngest tissues; deficiency symptoms are easily confused with herbicide injury phyt phys

defence response: the active response of a plant to pathogen attack; it includes the elements that inhibit pathogen development; a defence response is activated in compatible and incomaptible interactions phyt

definite host: the host in which the parasite attains sexual maturity phyt >>> host

deflexed: bent sharply downward bot

defoil: to strip a plant of leaves meth

defoliant: a chemical or method of treatment that causes only the leaves of a plant to fall off or abscise (e.g., it is applied before harvest of potato) agr

defoliated >>> defoliation

defoliation: the process of leaves being removed from a plant (e.g., to make harvest easier) bot

degeneracy of genetic code >>> degenerated code

degenerated code: a term applied to the genetic code because a given amino acid may be encoded by more than one codon gene

degermed: grains from which the embryo (germ) has been removed agr meth seed

degermination:the process of removing the grain's embryo (or germ) by mechanical devices, a term restricted almost exclusively to maize and rice milling meth

degradation: the progressive decrease in vigor of successive generations of plants, usually caused by unfavorable growing conditions or diseases; viruses may cause great loss of vigor; in agriculture, the change of one kind of soil to a more highly leached soil agr

degree of dominance >>> dominance

degree of freedom (DF): the number of items of data that are free to vary independently; in a set of quantitative data, for a specified value of the mean, only (n –1) items are free to vary, since the value of the nth item is then determined by the values assumed by the others and by the mean stat

degree of genetic determination: the portion of total variance that is genetically determined gene

dehiscence: the bursting open at maturity of a pod or capsule along a definite line or lines bot

dehiscent fruit >>> dehiscence

dehull: removal of outer seed coat (hull) or to remove the glumes of cereal caryopses seed

dehusk: to remove the husk (e.g., the leaf sheath of a maize cob or the outer layer of a coconut) seed

dehydration: the elimination of water from any substance phys

dehydrin(s): proteins produced during the late stages of plant embryo development and following any environmental stimulus involving dehydration phys

dehydrogenase: an enzyme that catalyzes the removal of hydrogen from a substrate phys

deletion: the loss of a chromosomal segment from a chromosome set; the size may vary from a single nucleotide to sections containing several genes cyto >>> deficiency >>> chromosome mutation

deletion mapping: the use of overlapping deletions to localize the position of an unknown gene on a chromosome or linkage map gene

deletion mutation: a mutation in which one or more bases are removed from the DNA sequence of a gene gene

deltoid: shaped like the Greek letter “delta” bot

demic selection: special type of intergroup selection that does not necessarily involve direct competition; it has an effect on the general genetic composition of a population if subsets of a population have different gene frequencies meth

democratic plant breeding - freie Pflanzenüchtung f: the converse of autocratic plant breeding; with democratic plant breeding, as many breeders as possible are producing as many cultivars as possible so that the farmer has a wide choice of cultivars; this approach is possible with the use of horizontal resistance because breeding for this kind of resistance is so easy; in many cases, farmers can do their own plant breeding

denaturation: reversible or irreversible alterations in the biological activity of proteins or nucleic acids that are brought about by changes in structure other than the breaking of the primary bonds between amino acids or nucleotides in the chain chem gene

denatured protein: a protein whose properties have been altered by treatment with physical or chemical agents chem

dendrogram: a genealogical diagram that resembles a tree; an evolutionary tree diagram may order objects, individuals genes, etc., on the basis of similarity evol meth >>> cluster analysis

dendrology: the branch of botany dealing with trees and shrubs bot

denitrification: the conversion of nitrate or nitrite to gaseous products, chiefly nitrogen and/or nitrous oxide, resulting in the loss of nitrogen into the atmosphere and therefore undesirable in agriculture chem agr eco

density-dependent: of or referring to a factor, such as nutrient shortage, that limits the growth of a population more strongly as the density of the population increases eco

density-dependent selection: the limiting of the size of a population (e.g., a vertical pathotype) by mechanisms that are also controlled by the size of population; this is a probable genetic mechanism for controlling the system of locking of the n/2 model, ensuring that all the n/2 biochemical locks and keys occur with an equal frequency;the rarity of a vertical pathotype or pathodeme is a reproductive advantage that leads to commonness; commonness is a reproductive disadvantage that leads to rarity eco

density gradient centrifugation: the separation of macromolecules or subcellular particles by sedimentation through a gradient of increasing density under the influence of a centrifugal force; the density gradient may either be formed before the centrifugation run by mixing two solutions of different density (e.g., in sucrose density gradients), or it can be formed by the process of centrifugation itself (e.g., in CsCl2 and Cs2SO4 density gradients) meth

density-independent: of or referring to a factor, such as weather, that can limit the size of a population but does not act more strongly as the density of the population increases eco

dent corn: a variety of maize, Zea mays ssp. indentata, having yellow or white kernels that become indented as they ripen agr

deoxyribonucleic acid (DNA): a nucleic acid, characterized by the presence of a sugar deoxyribose, the pyrimidine bases cytosine and thymine, and the purine bases adenine and guanine; its sequence of paired bases constitute the genetic code chem gene

deoxyribonuclease: any of several enzymes that break down the DNA molecule into its component nucleotides phys

dephosphorylation: the removal of a phosphate group from an organic compound, as in the changing of ATP to ADP chem phys

deployment: the physical movement of clones (ramets) or other genetic units from one site (usually a nursery) to another (usually plantations), often including their spatial configuration on the recipient site meth breed hort

derivative hybrid: a hybrid arising from a certain cross between two hybrids

dermal tissue system: the tissue system in plants that forms their outer covering bot

dermatogen: a specialized meristem in flowering plants in which floral induction begins; gives rise also to the epidermis bot

descendant: an individual resulting from the sexual reproduction of one parental pair of individuals gene

descent: the act, process or fact of descending gene

descriptor: an identifiable and measurable characteristic used to facilitate data classification, storage, retrieval, and use stat

desiccant: a chemical applied to crops that prematurely kills their vegetative growth; often used for legume seed crops so the seed can be harvested prior to normal plant senescence phys meth >>> defoliation >>> chemical desiccation

desiccate >>> desiccation

desiccation: the process of drying out phys >>> chemical desiccation

desinfectant: a physical or chemical substance for the destruction of pathogenic microorganisms phyt meth

desinfection: the destruction of germs of infectious diseases phyt

desiccation-intolerant seed >>> desiccation-tolerant seed

desiccation-tolerant seed: there are basically two types of seed: (a) desiccation-tolerant and (b) desiccation-intolerant; most of the plants produce desiccation-tolerant seeds, which means they can be safely dried for long-term storage; exceptions include many aquatic plants, large-seeded plants, and some trees (oaks, buckeyes etc.); any of which produce desiccation-intolerant seeds which will die if allowed to dry; they do not enter dormancy after maturing; instead, respiration and other physiological processes continue phys

desiccator: a glass jar with a air-tight lid that is used for drying out small quantities of plant tissue, such as seeds or root nodules, with a desiccating chemical; dry calcium chloride is a powerful desiccating chemical, but it is toxic and must be kept well separated from living tissues; alternatively, silica gel is harmless, but it is less powerful in its drying action meth cyto seed

designated host: a genetically stable host (i.e., a clone or pure line) which has been chosen for use in the one-pathotype technique in a horizontal resistance breeding program; ithas a resistance that is matched by the designated pathotype, which is cultured on that host for the entire duration of the breeding program;all the original parents of the breeding population are chosen on the basis of their susceptibility to the designated pathotype, which is used to inoculate every screening population; it ensures that all vertical resistances are matched during the screening for horizontal resistance, regardless of how the vertical resistance genes may have recombined during the crossing process phyt

design of experiments: it is a procedure, which can be used interactively to form experimental designs of various types; there several types of designs: (a) orthogonal hierarchical designs, such as randomized blocks, split-plots, or split-split-plots, (b) factorial designs (with blocking); these have several treatment factors and a single blocking factor (giving strata for blocks and plots within blocks); the blocks are too small to contain a complete replicate of the treatment combinations and so various interaction are confounded with blocks, (c) fractional factorial designs (with blocking); there are several treatment factors but the design does not contain every treatment combination and so some interactions are aliased; there can also be a blocking factor and some interactions will then be confounded with blocks, (d) lattice designs - designs for a single treatment factor with number of levels that is the square of some integer k; the design has replicates, each containing k blocks of k plots, and different treatment contrasts can be confounded with blocks in each replicate, (e) lattice squares; these are similar to lattices except that the blocking structure with the replicates has rows crossed with columns; different treatment contrasts can be confounded with the rows and columns in each replicate, (f) Latin squares; they are available for any number of treatments, where feasible, more than one orthogonal treatment factor can be generated to form Graeco-Latin squares, (g) Latin squares balanced for carry-over effects; these are relevant when the same plots or subjects are treated during several successive time periods, and there is interest both in the direct effect of a treatment during the period in which it is applied and its carry-over (or "residual") effect during later periods, (h) semi-Latin squares, i.e n × n Latin squares whose individual plots are split into k sub-plots to cater for a treatment factor with n × k levels; three types are available Trojan squares, interleaving Latin squares and inflated Latin squares, (i) alpha designs; these have a single treatment factor but there is no constraint on the number of levels; the blocking structure has replicates and blocks within replicates, (j) cyclic designs; these are designs with a single blocking factor which defines blocks that are too small to contain every treatment; usually there is a single treatment factor; however, in a cyclic superimposed designs two treatment factors can be considered, (k) balanced-incomplete-block designs where the experimental units are grouped into blocks such that every pair of treatments occurs in an equal number of blocks; all comparisons between treatments are made with equal accuracy, so the design is balanced, (l) neighbor-balanced designs that allow an adjustments to be made for the effect that a treatment may have on adjacent plots, (m) central composite designs used to study multi-dimensional response surfaces stat

desmosome: a plaquelike site on cell surfaces that function in maintaining cohesion with an adjacent cell bot biot

desynapsis: the premature separation of paired chromosomes during diplotene or diakinesis of meiotic prophase; it is often genetically controlled but can also be induced by special environmental conditions (e.g., heat) cyto

desyndesis >>> desynapsis

detasseling: artificially removing (cutting or pulling) the tassel of the female parent to prevent selfing during hybrid seed maize production meth seed >>> Picture 10

detergent: any synthetic organic cleaning agent that is liquid or water-soluble and has wetting-agent and emulsifying properties chem

determinate: descriptive of an inflorescence in which the terminal flower opens first, thus arresting the prolongation of the floral axis bot

deterministic process >>> stochastic

detoxicate >>> detoxication

detoxication: the metabolic process by which toxins are changed into less toxic or more readily excreted substances phys

detritivore: a consumer that relies on dead tissues for nutrients eco

developmental cycle: the gradual progression of phenotypic modifications of an organism during development phys

developmental genetics: the study of mutations that produce developmental abnormalities in order to gain understanding of how normal genes control growth, form, behavior, etc. gene

developmental stage >>> growth stages

devernalization: the reversion of vernalization by nonvernalizing temperatures or other means phys >>> vernalization

deviation: the departure of a quantity from its expected value stat

dextrin(e): a soluble gummy substance, formed from starch by the action of heat, acids, or enzymes chem phys

dextrose: an aldohexose monosaccharide that is a major intermediate compound in cellular metabolism; the dextrorotatory form of glucose, occurring in fruits and commercially obtainable from starch by acid hydrolysis chem phys

DF >>> degree of freedom

DFP >>> DNA fingerprint(ing)

DFR >>> dihydroflavonol 4-reductase

DH lines >>> doubled-haploid lines

diadelphous: showing stamens united in two sets by their filaments (e.g., in pea and bean flowers); nine out of ten stamens are usually united while one is by itself bot

diakinesis: the last stage in the prophase of meiosis I, when the paired homologous chromosomes are highly contracted but before they have moved onto the metaphase plate cyto >>> Figure 15

diallel: in either the complete or incomplete diallel, identities of both seed and pollen parents are maintained for each family meth >>> diallel cross >>> complete diallel >>> incomplete diallel

diallel cross: the crossing in all possible combinations of a series of genotypes meth >>> Table 24

diallel crossing group >>> crossing group(s)

diallelic >>> diallel cross

diallel mating >>> diallel cross

diapause: a period of dormancy phys; in insects, a state during which growth and development is temporarily arrested zoo

dibber >>> dibble

dibble: a pointed tool used to make holes in the ground for seeds and seedlings prep hort >>> pricking-out peg

dibble planting >>> dibbling

dibbling (seed): sowing in holes made by a pointed tool meth hort fore

dicentric: a chromosome or chromatid with two centromeres cyto >>> Figure 11

2,4-dichlorophenoxy acetic acid (2,4-D): a crystalline powder, C8H6O3Cl2, used for killing weeds and as a growth hormone phys biot

dichogamy: the condition in which male and female parts of a flower mature at different times bot

dichophase: the phase of the mitotic cycle in which a cell is determined for further mitotic differentiation or for special cell functions cyto

dichotomous ramification: branching, frequently successively, into two more or less equal arms bot

diclinous species: species having pistils and stamens on different flowers bot >>> Table 32

dicot: an abbreviated name for dicotyledon, which refers to plants having two seed leaves bot >>> dicotyledons

dicotyledons: plant species having two cotyledons; flower parts arranged in fours or fives or multiples thereof; net-veined leaves and vascular bundles in the stem arranged in a ring bot >>> Table 32

dicotyledonous >>> dicotyledons

dicotyledons: plant species having two cotyledons; flower parts arranged in fours or fives or multiples thereof; net-veined leaves and vascular bundles in the stem, arranged in a ring bot >>> Table 32

didiploid syn allotetraploid: two different diploid chromosome sets present in one cell or organism cyto

dieback: the death of tips or shoots due to damage or disease phys

differential centrifugation: a method(s) of separating subcellular particles by centrifugation of cell extracts at successively higher speeds; it is based on differences in sedimentation coefficients that are roughly proportional to particle size; in other words, large particles (nuclei, chloroplasts, or mitochondria) are sedimented at lower speeds than small particles (ribosomes) prep meth biot

dieback: the death of tips or shoots due to damage or disease phys

differential centrifugation: a method(s) of separating subcellular particles by centrifugation of cell extracts at successively higher speeds; it is based on differences in sedimentation coefficients that are roughly proportional to particle size; in other words, large particles (nuclei, chloroplasts, or mitochondria) are sedimented at lower speeds than small particles (ribosomes) prep meth biot

differential medium: an in vitro cultural medium with an indicator (e.g., a special dye), which allows various chemical reactions to be distinguished during plant growth meth

differential selection: the difference between a selected plant, family, or clone and the average of the population from which it is taken meth

differential staining: in microbiology, staining procedures that divide bacteria into separate groups based on staining properties; in cytology, staining procedures that divide chromosomes or genomes into separate segments based on structural and biochemical properties meth cyto

differential variety: a host variety, part of a set differing in disease reaction, used to identify physiologically specialized forms of pathogen phyt >>> differential host

differentiation of cells: the development of specialized kinds of cells from nonspecialized cells in a growing tissue bot phys

diffuse stage: a meiotic prophase stage in which the chromosomes become reorganized; they may almost disappear cyto

diffusion: passive movement of molecules from areas of high concentration of the molecule to areas of low concentration phy

dig: to break up and turn over piecemeal the soil or ground meth agr

digametic >>> heterogam(et)ic

digenic: it refers to an inheritance that is determined by two genes gene

digestibility: the attribute of forage biomass to be digested by grazing animals—an important selection criterion in forage crop breeding agr >>> Table 33

digitate: fingerlike; or a compound, with the members arising together at the apex of the support bot

digoxigenin (DIG): antigenic alkaloid from Digitalis spp. (foxglove), which is used to label DNA biot >>> in situ hybridization

digynoid: in parthenogenesis, the progeny derives from an unreduced egg cell bot

dihaploid: a haploid cell or individual containing two haploid chromosome sets—not to be confused with doubled-haploid cyto

dihybrid: a cross between individuals that differ with respect to two specified gene pairs gene

dihydroflavonol 4-reductase (DFR): bulb color in onions (Allium cepa) is an important trait, but the mechanism of color inheritance is poorly understood; a study showed that inactivation of the DFR gene at the transcriptional level resulted in a lack of anthocyanin production in yellow onions; a deletion mutation in the yellow DFR-A gene results in the lack of anthocyanin production in yellow onions too phys biot

diisosomic: a cell or an individual, which has a pair of homologous isochromosomes for one arm of a particular chromosome cyto >>> aneuploid >>> Figure 37

diisotrisomic: a cell or an individual that lacks one chromosome but carries two homologous isochromosomes of one arm of a particular chromosome cyto >>> aneuploids >>> Figure 37

dikaryon: a dinucleate cell cyto

dikaryotic: a cell showing two nuclei bot

dimer: a protein that is made up of two polypeptide chains or subunits paired together chem

dimerization >>> dimer

dimethyl sulfoxide (DMSO): a liquid solvent, C2H6OS, approved for better penetration of specific substances through the cell wall chem meth

dimorph >>> dimorphism

dimorphism: the occurrence of two forms of individuals within one population or other taxa (e.g., sexual dimorphism or the presence of one or more morphological differences that divide a species into two groups) bot

dimorphous branching - zweiartige Verzweigung f: some crop species (e.g., arabica coffee, cotton, black pepper) have two kinds of branches; the orthotropic branch is the branch that grows vertically, and it produces side branches, called plagiotropic branches, that tend to grow horizontally; it is usually the plagiotropic branches that bear the flowers and seed; cuttings must be taken from the orthotropic branch, and this severely limits vegetativ propagationbot meth hort

dioecious: possessing male and female flowers or other reproductive organs on separate, unisexual, individual plants (e.g., in hemp or spinach) bot

dioecism: the phenomenon of plants showing either male or female sex organs bot

diphasic: chromosomes that show both euchromatic and heterochromatic segments bot

diphyletic: a group of species that share two ancestries evol >>> monophyletic >>> polyphyletic

diplandroid: in parthenogenesis, the progeny derives from an unreduced sperm cell bot

diploid: a cell with two chromosome sets or an individual with two chromosome sets in each cell; a diploid state is written as “2n” to distinguish it from the haploid state “n” gene >>> Table 1 >>> Figure 8

diploid parthenogenesis: a type of gametophyte apomixis by which a diploid embryo sac cell results in a diploid embryo; the diploid condition is the result of cytogenetic mechanisms occurring in the egg stage bot >>> Figure 28

diploidization: in polyploids, a natural or induced mechanism in which the chromosomes pair completely or partially as bivalents, although polyploid sets of chromosomes are present; it may be caused by a structural differentiation of homologous chromosome sets or by genetic control; for example, in bread wheat three homoeologous genomes are available (AABBDD); they do not pair as hexavalents but exclusively as bivalents cyto

diploidizing mechanism: a mechanism whereby the chromosomes of a polyploid sometimes form exclusively or partly bivalents instead of multivalents during meiosis; usually it is under strictly genetic control (e.g., the Ph [pairing homologous] locus on chromosome 5B of hexaploid wheat) cyto

diploidy: the presence of two homologous sets of chromosomes in somatic cells cyto >>> Table 1 >>> Figure 8

diplonema >>> diplotene

diplontic >>> diploid

diplophase: the diploid generation phase after fertilization to meiosis cyto

diplospory: a type of agamospermy (apomixis) in which a diploid embryo sac is formed from archesporial origin bot >>> Figure 28

diplotene: the stage in the prophase of first meiosis, when the paired homologous chromosomes separate except where they are held together by chiasmata cyto

dipping: the immersion of seedling roots in a solution or water prior to planting fore hort meth

direct embryogensis: embryoid formation directly on the surface of zygotic or somatic embryos or on seedling plant tissues in culture without an intervening callus phase biot

direct organogenesis: organ formation directly on the surface of relatively large intact explants without an intervening callus phase biot

directed dominance >>> directional dominance >>> dominance

directional cloning: in biotechnology, DNA inserts and vector molecules are digested with two different restriction enzymes to create noncomplementary sticky ends at either end of each restriction fragment; it allows the insert to be ligated to the vector in a specific orientation and prevents the vector from recircularizing biot

directional dominance: a type of dominance in which the majority of dominant alleles have positive effects in one direction gene

directional mutation: a genetic change that favors a certain genotype or population gene

directional selection: selection resulting in a shift in the population mean in the direction desired by the breeder meth

dirty seed: endophyte-infected seeds (e.g., in grass) seed >>> clean seed

disaccharide: any of a group of carbohydrates, as sucrose, that yield monosaccharides on hydrolysis chem phys

disassortative mating: occurs if the plants mating resemble each other less than plants belonging to pairs of random plants, with regard to some trait gene >>> assortative mating

disbud: removing buds, shoots, or growing tips (with finger and thumb) of a tree, vine, or flowering plant to encourage production of sideshoots or high-quality flowers and fruits; pinching out is also used when small side shoots are completely removed; it is done when single stems are desired, especially when training to form the “trunks” of standard (tree-form) specimens hort

disc floret: a small flower, usually one of a dense cluster (e.g., sunflower) bot

disc flower: the tubular flowers of the head, as distinct from the ray (e.g., in Asteraceae or sunflower) bot

disc grain-grader: discs revolve through a seed mass and a certain size of seeds are lifted and discharged, while the other size (e.g., the longer ones) is rejected by the disc indents seed

disc plough >>> disk plough

discontinuous character: variation in which discrete classes can easily be recognized (e.g., flower color, straw length) gene >>> qualitative character

disease: a condition in which the use or structure of any part of a living organism is not normal; harmful deviation from normal functioning of physiological processes; six types of causal agents can be considered: (1) fungi, (2) bacteria, (3) viruses, (4) nematodes, (5) insects, and (6) plant parasites phyt >>> seed-borne pathogens


disease avoidance: avoiding the disease by, for example, growing the crop sufficiently early so that the vulnerable part of the plant’s growing cycle is over before the disease-causing organism arrives in the area; this stops the disease from starting; it is sometimes called “passive resistance” phyt

disease control: several types of disease control can be classified: (1) disease resistance, (2) protection, (3) avoidance, (4) exclusion, (5) eradication, (6) therapy phyt


disease cycle: a cyclical sequence of host and parasite development and interaction that result in disease and in reproduction of the pathogen phyt


disease eradication: this control measure is applied to a situation in which the disease is present in the area; it involves removing the disease by, for example, burning all stubble of the diseased crop, in order to prevent transfer of the disease from the previous crop to the next season phyt


disease escape: for a variety of reasons, some individuals in a screening population may remain free of pests or disease; it also known as chance escape; this phenomenon can be very misleading because it is so easily confused with resistance phyt

disease protection: involves protecting the plant with a chemical; this is applied before the disease starts and prevents the beginning of problems; systemic fungicides can penetrate and move inside the plant; they therefore have a greater exposure to the pathogenic organism; some are taken up by roots, other by leaves phyt >>> systemic pesticide


disease resistance: the ability to resist disease or the agent of disease and to remain healthy phyt


disease therapy: this applies to removing the particular part of the plant that is diseased; often applied to large and valuable plants, such as fruit trees, where a diseased branch may be removed by a tree surgeon phyt


disease triangle: the three conditions required for a disease to occur, namely: a susceptible host, a suitable pathogen and an appropriate environment phyt

disinfectant: a chemical treatment used to disinfect seed for planting; it is commonly useful for surface-borne pathogens seed meth

disjunction (of daughter chromosomes): the separation of homologous chromosomes at the anaphase stage of mitosis and meiosis, and movement toward the poles of nuclear spindle cyto

disjunctional separation >>> alternative disjunction

disk: enlarged growth of the head made up of a circular arrangement of fused petals (e.g., in sunflower) bot >>> disc flower

disk flower >>> disc flower

disk plough: a plough with saucer-shaped units for breaking the soil agr

dislocation: the displacement of a chromosome segment away from its original position in the chromosome cyto

disome: a cell or an individual showing the two homologous sets of chromosomes cyto >>> aneuploid >>> Figure 37

disomic >>> disome

disomy >>> disome

dispermy: the entering of two sperm cells into one egg cell bot

dispersal: the spread of a pathogen within an area of its graphical range phyt

dispersing agent: a chemical added to a pesticide formulation to aid the efficient distribution of particles of the active ingredient phyt prep

disporic: having two spores bot

disruptive selection: a selection that changes the frequency of alleles in a divergent manner, leading to the fixation of alternative alleles in members of the population; the result after several generations of selection should be two divergent phenotypic extremes within the population meth

dissecting microscope: usually, a low-power microscope (50x magnification) used to facilitate dissection, examination, or excision of small plant parts; however, in recent biotechnology high-power microscopes also are applied for dissections prep

dissepiment: a partition within an organ of a plant (e.g., the membrane that separates sections of the orange and other citrus fruits) bot

dissemination: the spread of seeds or spores eco >>> dispersal

dissimilation >>> assimilation

distal: farthest from the point by which it is attached to the starting point gene cyto

distance isolation: several plants can be protected from cross-pollination by separation by a certain distance, such as lettuces (~25 feet) or eggplants (~50 feet); insect-pollinated plants, such as the cabbage family (collards, broccoli, etc.), squashes and okra require from ¼ to 1 mile for complete safety; maize, a wind-pollinated plant, can require a mile or more for safe distance isolation and members of the beet family may need as many as 5 miles; the exact distance for safely isolating a particular crop depends on a number of factors, e.g., the type of plant and how it is pollinated (i.e., wind, insects, selfing or a combination of these), the location, climate, prevailing wind patterns and surrounding terrain and vegetation features, the relative size of plantings etc. meth

distant hybridization: the crossing and/or hybridization of members of different genera meth

distichous: in two vertical ranks bot

distinguishable hybrid: a type of hybrid in which intermediate inheritance is phenotypically expressed (i.e., the heterozygous gene constitution is visible by the phenotype) gene

distyly: the presence of either pin or thrum flowers; pin x pin and thrum x thrum crosses are incompatible due to alleles at a single locus; the thrum morphology is controlled by a dominant allele S and the pin morphology by the recessive alleles s bot >>> self-incompatibility

disulfide bridge: a covalent bond formed between two sulfur atoms; it is a particular feature of peptides and proteins, where it is formed between the sulfydryl groups of two cysteine residues, helping to stabilize the tertiary structure of these compounds chem

ditelocentric >>> ditelosomic

ditelomonotelosomic: a cell or an individual that has a pair of telocentric chromosomes for one arm and a single telocentric chromosome from the other arm cyto >>> aneuploid >>> Figure 37

ditelosomic: a cell or an individual that has two telocentrics of one chromosome arm cyto >>> aneuploid >>> Figure 37

ditelotrisomic: a cell or an individual that has two telocentric chromosomes of one arm plus one complete chromosome of the homologue cyto >>> aneuploid >>> Figure 37

ditertiary compensating trisomic: a cell or an individual with a compensating trisomic chromosome in which a missing chromosome is compensated by two tertiary chromosomes cyto >>> Figure 14

diurnal rhythm >>> circadian rhythm

divalent >>> bivalent

divergent: set at an angle to one another herring-bone fashion, as in the lateral spikelets of the two-row barley spike bot

diversifying selection: selection in which two or more genotypes show optimal adaptation under different environments meth

diversity arrays technology (DArT)marker: a DArT marker is a segment of genomic DNA, the presence of which is polymorphic in a defined genomic representation; DArT markers are biallelic and behave in a dominant (present vs absent) or co-dominant (2 doses vs 1 dose vs absent) manner; to identify the polymorphic markers, a complexity reduction method is applied on the metagenome, a pool of genomes representing the germplasm of interest; the genomic representation obtained from this pool is then cloned and individual inserts are arrayed on a microarray resulting in a ‘discovery array’; labelled genomic representations prepared from the individual genomes included in the pool are hybridized to the discovery array; polymorphic clones (DArT markers) show variable hybridization signal intensities for different individuals; these clones are subsequently assembled into a ‘genotyping array’ for routine genotyping; the methodwas developed to provide a practical and cost-effective whole-genome fingerprinting tool; DArT has three key attributes of interest to plant breeders and scientists studying and managing genetic diversity: (a) it is independent from DNA sequence, (b) the genetic scope of analysis is defined by the user and easily expandable, and (c) the method provides for high throughput and low-cost data production; the discovery of polymorphic DArT markers and their scoring in subsequent analysis does not require any DNA sequence data; it makes the method applicable to all species, regardless of how much DNA sequence information is available for that species; however DArT markers are sequence-ready clones of genomic DNA; for each species, the method is developed on the ‘metagenome’, the pooled genomes from the germplasm of interest to the user, e. g., the metagenome may include DNA from the cultivated varieties of a particular region or the lines used in a breeding program; alternatively, the metagenome may cover the genetic diversity within the entire species and even extend to its wild relatives; importantly, the diversity surveyed by DArT can be expanded if new individuals with marked genetic differences are incorporated into the analysis at a later stage; in DArT, several hundred polymorphic markers are identified in parallel; the efficiency of this marker discovery effort is only dependent on the level of genetic diversity within the species (5-10 % of wheat and barley DArT clones and 25-30 % of cassava DArT clones were polymorphic); the microarray platform enables a high level of multiplexing: ~5,000-8,000 genomic loci are typically surveyed in parallel in single-reaction assays to discover polymorphic markers; DArT markers can be used as any other genetic marker; with DArT, comprehensive genome profiles are becoming affordable for virtually any crop, regardless of the molecular information available for the crop; DArT genome profiles are very useful for the recognition and management of bio-diversity; DArT genome profiles enable breeders to map QTL in one week, thereby allowing them to focus on the most crucial factor in plant breeding: reliable and precise phenotyping; once many genomic regions of interest are identified in many different lines, DArT profiles accelerate the introgression of a selected genomic region into an elite genetic background; furthermore DArT profiles can be used to guide the assembly of many different regions into improved varieties; for that purpose, dense genome cover is essential in order to follow many regions simultaneously meth biot

division: a method of propagation by which a plant clump is lifted and divided into separate pieces; it includes roots and a growing point meth hort

DMSO >>> dimethyl sulfoxide

DNA >>> deoxyribonucleic acid

DNA banking: beside the in situ and ex situ conservation of plant genetic resources it is a complementary  conservation strategy and an effective tool for more efficient management of genebanks and conservation research; however, it is still not a common practice since technical capacity and financial resources are currently limited, particularly in developing countries; in future DNA banks can be the libraries for reference sequences  that can be applied to estimate genetic diversity and relative change within populations or to identify samples when genotypes confound morphologically-based identification; DNA is an unusually stable biomolecule that often outlasts the organism it encodes; DNA banks provide an accessible means for genetic characterization and electronic integration  of many existing biomaterial collections seed biot

DNA clone: a section of DNA that has been inserted into a bacterium, phage, or plasmid vector and has been replicated many times gene

DNA content: usually, the total DNA amount per nucleus, given as picograms cyto

DNA-DNA hybridization: the annealing of two complementary DNA strands to produce hybrid nucleic acid molecules; it is used to identify the base sequences in two polynucleotide chains from different sources gene meth

DNA hybridization: base pairing of DNA from two different sources; in biotechnology, a technique for selectively binding specific segments of single-stranded (ss) DNA or RNA by base pairing to complementary sequences of ssDNA molecules that are trapped on a nitrocellulose membrane gene biot

DNA-amplified fingerprinting: a technology based on amplification of random genomic DNA sequences achieved by a single short (5-8 bases) oligonucleotide primer of arbitrary sequence; it produces a characteristic spectrum of short DNA pieces of varying complexity that are resolved on polyacrylamide gel (PAGE) following silver staining; it is used to detect genetic differences between genotypes as well as for detecting polymorphism even between organisms that are closely related, such as near isogenic lines biot meth >>> DNA fingerprint(ing)

DNA barcoding: the use of a short DNA sequence or sequences from a standardized locus (or loci) as a species identification tool of plants; it is useful for identification of different life stages, e.g. seeds and seedlings; for identification of fragments of plant material, for biosecurity and trade in controlled species, or for plant inventory and ecological surveys; barcoding of animals is already in progress using the cytochrome c oxidase 1 (cox1 ) gene; in plants, it is mor difficult since there is often no sequence variation among species within a genus, and therefore the gene is not suitable as a plant barcode meth biot

DNA fingerprint(ing) (DFP): the unique pattern of DNA fragments identified by Southern hybridization (using a probe that binds to a polymorphic region of DNA) or by polymerase chain reaction (PCR) using primers flanking the polymorphic region meth gene >>> DNA-amplified fingerprinting

DNA library >>> clone library

DNA ligase (polynucleotide ligase): an enzyme that creates a phosphodiester bond between the 5'-PO4 end of one polynucleotide and the 3'-OH end of another, thereby producing a single, larger polynucleotide biot

DNA methylation: the methylation of DNA bases by endogenic methylases gene chem

DNA micro arrays: a powerful, versatile and economical molecular technique for screening of genetic aberrations; high-density gene sequences are printed onto glass slides; fluorephore-labeled genomic or complimentary DNA (cDNA) is hybridized to slides with fixed signature patterns and resolved using computer driven fluorescent image biot

DNA moving picture(s): spectacular image(s) of intact chromosomal DNA molecules as long as 100 megabases biot

DNA packing: the highly organized way in which large amounts of DNA are packed into the cells of eukaryotic organisms gene

DNA polymerase: any enzyme that catalyzes the synthesis of DNA strands from deoxyribonucleoside triphosphates using single-stranded DNA as a template gene phys

DNA polymerase I (KORNBERG enzyme): used for nick translation and for the production of the KLENOW fragment biot

DNA polymorphism: one of two or more alternate forms (alleles) of a chromosomal locus that differ in nucleotide sequence or have variable numbers of repeated nucleotide units biot


DNA probe: a more or less defined piece of DNA that is used for DNA-DNA or DNA-RNA hybridization experiments gene meth

DNA repair: the reconstruction of DNA molecule after different sorts of DNA-strand damages by endogenic enzymes; it is involved in the recombination process and promotes the survival of an organism after partial DNA damage gene

DNA replication: the process whereby a copy of a DNA molecule is made, and thus the genetic information it contains is duplicated; the parental double-stranded DNA molecule is replicated semiconservatively (i.e., each copy contains one of the original strands paired with a newly synthesized strand that is complementary in terms of AT and GC base pairing) gene

DNase: nuclease specific for DNA biot >>> deoxyribonuclease

DNase I: an endonuclease that makes random single-stranded nicks in DNA; used for nick translation biot

DNA sequencing: methods and procedures for determining the nucleotide sequence of a DNA fragment and/or chromosome biot gene

9-dodecenyl acetate: a pheromone containing the (E) and (Z) isomers; it is for use in manufacturing pheromone based products to control moths; the pheromone is used in traps, dispensers, and sprays to help control destructive moths in forests and agricultural applications fore agr phyt 

dome: in cereals, the zone of cells at the tip of the apical meristem (shoot apex), which, by cell division, forms the site for production of leaf and spikelet primordia bot >>> meristematic tip

domesticated populations >>> domestication

domestication: the selective breeding by humans of species in order to accommodate human needs evol

dominance: the quality of one of a pair of alleles that completely suppresses the expression of the other member of the pair when both are present; the degree of dominance is expressed by the ratio of additive genetic variance to total phenotypic variance; in case the ratio equals 1, the trait shows complete dominance, if the ratio is greater than 1, the trait shows overdominance, if the ratio is less than 1, the trait shows incomplete dominance gene >>> Tables 2, 6, 9, 20, 21

dominance hypothesis: in hybrid breeding, dominant alleles of genes that should have stimulating effects on heterosis, while recessive ones should show inhibitory effects gene >>> dominance >>> Figure 18

dominance-recessiveness relation >>> dominant

dominance variance: that portion of the genetic variance attributable to dominant gene effects stat >>> dominance

dominant: in diploid organisms, a gene that produces the same phenotypic character when its alleles are present in a single dose (heterozygous) per nucleus, as it does in a double dose (homozygous); a gene that is masked in the presence of its dominant allele in the heterozygous state is called to be recessive to that dominant gene >>> dominance >>> Figures 6, 18 >>> Tables 6, 20, 21

dominant epistasis: one dominant factor A is epistatic of another factor B, or B is hypostatic to A gene >>> Table 6

donator >>> donor

donor: an individual, line, population, or variety from whom pollen or genetic material is used for transfer to another meth

donor parent: the parent from which one or a few genes are transferred to the recurrent parent in backcross breeding meth

donor plant: the source plant used for propagation, crossing, etc., whether a simple individual, an explant, graft, or cutting meth

dormancy: a resting condition with reduced metabolic rate found in nongerminating seeds and nongrowing buds phys

dormant >>> dormancy

dormant bud >>> dormancy

dormant seeding: sowing during late autumn or early winter after temperatures become too low for seed germination to occur until the following spring meth agr

dormant spray: a pesticide applied to dormant, leafless plants to control insects and diseases phyt

dorsal: in general, upon or relating to the back or outer surface of an organ (abaxial); the side of the caryopsis on which the embryo is situated bot >>> adaxial

dosage compensation: a genetic process that compensates for genes that exist in two doses in the homozygous dominants, so that the heterozygotes produce the same amount of gene product as the homozygotes gene

dosage effect: the influence upon a phenotype of the number of times a genetic element is present gene

dose effect >>> dosage effect

dot-blot analysis: a variant of the Southern transfer; different concentrations of RNA or DNA may be determined; nonradioactive DNA will be denatured and with different concentrations transferred to nitrocellulose filters; only small dots are transferred; that DNA may hybridize with radioactively labeled probe; after autoradiography, the intensity of blackness is used as a simple measure of DNA concentration or DNA homology meth biot

double cropping: the more or less contemporary growing of two crops on the same field; for example, it might be to harvest a wheat crop by early summer and then plant maize or soybeans on that acreage for harvest in autumn; this practice is only possible in regions with long growing seasons agr

double cross: a cross between two F1 hybrids; the method used for producing hybrid seed; four different lines (A, B, C, D) are used; A x B དྷ AB hybrid and C x D དྷ CD hybrid; the single-cross hybrids (AB and CD) are then crossed and the double-cross hybrid (ABCD) seed is used for the commercial crop meth seed >>> Figure 31

double-cross hybrids: hybrids resulting from crossing two single cross hybrids seed >>> double cross >>> Figures 22, 31

double crossing-over: the situation in which two crossing-overs take place within a tetrad cyto gene

double digestion: cleavage of a DNA molecule with two different restriction enzymes biot

double ditelocentric: the phenomenon in which both arms of a certain chromosome are present as telocentrics, and each telocentric with its homologue cyto >>> Figure 37

double fertilization: the union of one sperm nucleus with the egg nucleus to form the diploid zygote and of the other sperm nucleus with the two polar nuclei to form a triploid endosperm nucleus; the male gametophyte, pollen grain plus pollen tube, actually contains three sperm nuclei, but one, the vegetative nucleus, degenerates once double fertilization has been accomplished cyto >>> Figure 35

double flower: flowers that have more than one row of petals; stamens and sometimes the pistils are transformed into petals or sometimes the petals split to form several more; completely double flowers have usually lost their reproductive organs and are therefore unable to produce seeds; these varieties of plants are bred to stay fresh longer than single flowers when cut; commonly, plants do not show double flowers; they can only be formed when three specific genes are simultaneously mutating; these genes are the main regulators for flower formation; their DNA sequences are almost identical; by induced mutations and subsequent combination of those genes double flowers can be induced (e.g., in Arabidopsis) bot gene hort

doubled haploid: a diploid plant, which results from spontaneous or induced chromosome doubling of a haploid cell or plant, usually after anther or microspore culture by using different means biot >>> Figures 17, 26 >>> Table 7

doubled haploid: a diploid plant that results from spontaneous or induced chromosome doubling of a haploid cell or plant, usually after anther or microspore culure by using different means biot >>> Figures 17, 26 >>> Table 7

doubled-haploid lines (DH lines): homozygous lines derived from haploidization and doubling again the chromosome number biot meth >>> doubled haploid (DH) method >>> Figures 17, 26 >>> Table 7

doubled haploid (DH) method: a method used to speed up the production of homozygotes and to decrease the population size for selection; in other words, generating haploid plants by parthenogenesis or by anther culture followed by doubling of the number of their chromosomes (spontaneously or induced) biot meth >>> doubled-haploid lines (DH lines) >>> Figures 17, 26 >>> Table 7

duble helix: a structure of DNA consisting of two helices around a common axis chem gene

double hybrid >>> double cross

double monoisosomic: the presence of two isochromosomes, one for each arm; it can derive from a double monotelosomic individual cyto >>> Figure 37

double monotelosomic: the presence of two telocentrics, one for each arm cyto

double recessive: an individual that is homozygous for a recessive allele (e.g., aa), as opposed to homozygous for a dominant allele (e.g., AA) gene

double reduction: the genetic outcome of chromatid segregation, as opposed to chromosome segregation, whereby two sister-chromatid segments are included in the same meiotic product cyto

double telotrisomic: the presence of two telocentrics, one for each arm of a missing whole chromosome, but together with the complete homologue cyto >>> aneuploid >>> Figure 37

doubling time: the average time required to double the number of individuals of a population gene

dough quality >>> “strong” flour

dough strength >>> “strong” flour

downstream: a term used for description of the position of a DNA sequence within a DNA or protein molecule; it means that the position of the sequence lies toward the direction of the synthesis of a DNA or protein molecule gene

downy: covered with soft hairs or down bot

drain: in order to remove water from the soil by artificial means (e.g., drainage ditches, buried perforated plastic pipes, or a gravel sump) meth agr

drainage: excess of water can be harmful to crop production; wet soils are usually low in temperature and low in oxygen content; drainage can be facilitated by open ditches or different subsoil drains agr

dressing: manure, compost, or other fertilizers agr

drift: changes in gene and genotypic frequencies in small populations due to random processes gene

drill: a machine for seeding crops by dropping them in rows and covering them with earth; the term is also used for a row of seeds deposited in the earth (i.e., the trench or channel in which the seeds are deposited); in general, to sow seeds in rows (i.e., the field was drilled, not sown broadcast) agr

drill-row >>> drill

drip irrigation - Tropfbewässerung f: a system of watering by which moisture running through a porous hose; the water is slowly released through tiny holes or emitters to the plant roots; it is one of the most efficient of irrigation technologies agr

drought hardening: adapting plants to survive periods of time with little or no water by stepwise reducing water supply or germinating and/or growing under insufficient moisture conditions meth >>> Table 33

drought resistance - Trockenresistenz f: the ability of a plant to withstand drought; this property can be very valuable in areas of uncertain rainfall, e.g., sorghum has greater drought resistance than maize, and is grown in many semi-arid areas for this reason agr

drought stress >>> stress protein(s)

drought-tolerant - trockentolerant adj: plants that can survive periods of time with little or no water, it appears that seed and cereal crops are typically most drought sensitive around the flowering stage; in peas, for example, the reduction in yield can be as much as 10 % for a single so-called “stress day” during the flowering phase; a “stress day” is an expression of how much the actual transpiration has been reduced compared with the potential transpiration; it was found that the flowering, but thirsty plants had fewer grains, because the young seed ovules were aborted; this is due to the specific genes controlling the plant metabolism being down-regulatedagr >>> Table 33

drupe: a fleshy fruit, such as a plum, cherry, coconut, walnut, peach, or olive, containing one or more seeds, each enclosed in a stony layer that is part of the fruit wall (hard endocarp) bot

dry farming: a method of farming in arid and semiarid areas receiving less than 500 mm rainfall the year without using irrigation; the land being treated so as to conserve moisture; the technique consists of cultivating a given area in alternate years, allowing moisture to be stored in the fallow year; moisture losses are reduced by producing a mulch and removal of weeds agr

dry matter (DM) - Trockensubstanz f: the substance in a plant or plant material remaining after oven drying to a constant weight at a temperature slightly above the boiling point of water meth

dry season - Trockenperiode f: a period each year during which there is little precipitation eco

dry weight - Trockengewicht n: moisture-free weight meth agr

dsDNA: double-stranded DNA biot

dummy trial >>> blindfold (trial)

duplex type: a polyploid plant that shows two dominant alleles for a given locus gene >>> nulliplex type >>> autotetraploid >>> Table 3

duplicate genes: two or more pairs of genes in one diploid individual, which alone or together produce identical effects gene >>> Figure 36

duplication: a chromosomal aberration in which more than one copy of a particular chromosomal segment is produced within a chromosome set gene >>> Figure 36

duplication of germplasm: a duplicated seed sample that is prepared for safety reasons; usually the two samples are kept at different locations seed

durable resistance: resistance that remains effective and stable during the agronomic life of a crop; this type of resistance is usually determined by several genes and is a main target of resistance breeding phyt

DUS testing: the methods and standards of the identification and description of varieties are elaborated by different teams of the international organization UPOV established for the protection of plant varieties; the so-called TG/01/2/1/ contains the most important prescriptions; these procedures, prescriptions, and methods are called DUS testing (D = distinctness, U = uniformity, S = stability); for the legal protection of varieties, the candidates (1) have to have names that have not yet been used for the registration of recognized varieties, (2) must have been discovered distinct of the other “known” varieties (D), (3) have to be uniform and homogeneous (U), and (4) have to be stable (S); the characteristics involved in DUS testing can be divided into two main types: (a) measured characteristics and (b) visually observed (bonitated, qualitative) characteristics; the measured characteristics have values on the continuous scale; visually observed data have values in the interval 1, 2 to 9; in other words, visually observed traits are of the so-called ordinal type, while measured data are on the so-called interval or ratio scale; phenological data must also be mentioned as a special type of measured characteristic (e.g., number of days until flowering, etc.) seed

dust: a method of pesticide control in which a dry substance is applied by spraying seeds, tubers, or bulbs phyt

dust separator >>> aspirator

duster: a device consisting of a bin, a wand with a nozzle, and a crank mechanism; it is used for applying dust or powder to plants phyt meth

dusting >>> dust

dust separator >>> aspirator

dwarf fruit trees: a small fruit tree reaching a height at maturity of 150-200 cm; bred for convenient harvest technology as well as bearing early and normal fruits meth hort >>> Table 33

dwarfing gene: one category of genes that control the height of the plant gene >>> Table 33

dyad: a pair of cells (i.e., one of the products of the disjunction of the tetrads at the first meiotic division, contained in the nuclei of secondary gametocytes) cyto

dyeing flowers: blossoms capable of producing dyes hort

dysgenic >>> eugenic

dysploid: a plant or species in which the chromosome number is more or less than the expected normal euploid number cyto

dysploidy: abnormal ploidy (e.g., the appearance of diploid or triploid individuals in a normally tetraploid population or of triploid and tetraploid ones in a normally diploid population) cyto >>> anisoploid

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