S  |   T  |   U  |   V

S

sanitation    
the destruction or removal of infected and infested plants or plant parts; decontamination of tools, equipment, containers, work space, hands, etc.

sap transmission
the transmission of pathogens, usually viruses, by rubbing sap from an infected plant onto a healthy plant to cause infection

saprobe     (adj. saprobic)  
an organism that obtains nourishment from nonliving organic matter (see also saprophyte, saprotroph)

saprophyte    (adj. saprophytic)
an organism that obtains nourishment from nonliving organic matter (see also saprobe, saprotroph)

saprotroph (adj. saprotrophic)
an organism that obtains nourishment from nonliving organic matter (see also saprobe, saprophyte)

sapwood 
the physiologically active zone of wood contiguous to cambium (contrasts with heartwood)

SAR (acronym for systemic acquired resistance)
the reduced disease symptoms on a portion of a plant distant from the area where a hypersensitive response occurred or other stimulus was applied; a rapid and coordinated defense response against a variety of pathogens as a signal travels throughout the plant (see induced systemic resistance)

scab    
a roughened, crustlike diseased area on the surface of a plant organ

scald  
a necrotic condition in which tissue is usually bleached and has the appearance of having been exposed to high temperatures

scion  
a portion of a shoot used for grafting onto the root stock (contrasts with rootstock)

sclerenchyma (adj. sclerenchymatous)  
a plant tissue made up of thick-walled nonliving cells

sclerotium   (pl. sclerotia)    
a vegetative resting body of a fungus, composed of a compact mass of hyphae with or without host tissue, usually with a darkened rind

scorch    
any symptom that resembles the result of flame or fire on the affected part, often seen at the margins of leaves

secondary growth
the growth in vascular plants from lateral meristems, resulting in wider stems and branches

secondary infection 
an infection resulting from the spread of infectious material produced after a primary infection or from secondary infections without an intervening inactive period

secondary inoculum 
the inoculum produced by infections that occurred during the same growing season (contrasts with initial inoculum, primary inoculum)

secondary metabolite
a compound produced in microbes (e.g., mycotoxins, syringomycins) or plants (e.g., caffeine or nicotine) that is not necessary for normal growth and development

secondary organism (pathogen)
an organism that multiplies in already diseased tissue but is not the primary pathogen

secondary phloem
the phloem produced by the vascular cambium in stems and branches of woody plants

secondary pollutant  
an air pollutant that must be chemically produced from other air pollutants, e.g., ozone (O₃), which is a product of a photochemical reaction of exhaust products from combustion engines in the atmosphere (contrasts with primary pollutant)

secondary root  
a branch from a primary root

secondary xylem 
the xylem produced by the vascular cambium in stems and branches of woody plants; also known as wood

sedentary    
remaining in a fixed location (contrasts with migratory)

seed
a ripened ovule consisting of an embryo and stored food enclosed by a seed coat

seed bank
an organization that preserves and maintains species and cultivars of plants for use by plant breeders; the collection of nongerminated seeds in a soil (weed seed bank)

seed treatment
the application of a biological agent, chemical substance, or physical treatment to seed, to protect the seed or plant from pathogens or to stimulate germination or plant growth

seedborne
carried on or in a seed

selective medium  
a culture medium containing substances that specifically inhibit or prevent the growth of some species of microorganisms or promote the growth of some organisms over others

self-fertilization
a process in which sexual reproduction occurs as a result of the fusion of sex cells produced by the same individual (contrasts with cross-fertilization)

self-pollination
the transfer of pollen from the anthers to a stigma of the same individual plant (contrasts with cross-pollination)

senesce (adj. senescent, n. senescence)
to decline, as with maturation, age, or disease stress

sepal 
one of the modified leaves comprising a calyx

septate  
with cross walls; having septa (contrasts with coenocytic, non-septate)

septum   (pl. septa; adj. septate)   
a dividing wall; in fungi, a cross wall

serology (adj. serologic) 
a method using the specificity of the antigen-antibody reaction for the detection and identification of antigenic substances and the organisms that carry them

serrate
having edges with teeth, like a saw

sessile
pertaining to a leaf, leaflet, flower, floret, fruit, ascocarp, basidiocarp, etc., without a stalk, petiole, pedicel, stipe or stem; (of nematodes) permanently attached; not capable of moving about

seta    (pl. setae)   
a bristle or hairlike structure, usually deep yellow or brown and thick-walled

severity values
a means to quantify accumulating opportunities for pathogen infection (e.g., infection periods), with reference to a predetermined threshold that, when met, triggers a disease-management activity (e.g., a fungicide application); used in disease prediction or forecasting

sexual reproduction
reproduction involving fusion of two haploid nuclei (karyogamy) to form a diploid nucleus, followed by meiosis (reduction division) back to haploid nuclei at some point in the life cycle, resulting in genetic recombination (contrasts with asexual reproduction)

sexual spore
a spore produced during the sexual cycle

sexually compatible
able to be cross-mated or cross-fertile

shepherd’s crook
the curved, apical portion of a blighted stem (see also crozier)

shot-hole    
a symptom in which small lesions fall out of leaves, giving the leaf the appearance of being hit by buckshot

sieve element (syn. sieve tube element)    
a tube-shaped living cell in the phloem, functioning in the transport of dissolved organic substances in the plant

sign    
an indication of disease from direct observation of a pathogen or its parts (contrasts with symptom)

single gene resistance
resistance conferred by a single gene (see also monogenic resistance) (contrasts with multigenic resistance, oligogenic resistance, polygenic resistance)

slime mold  
an informal term for a nonpathogenic funguslike organism that forms a vegetative amoeboid plasmodium and spores (see also myxomycetes, Myxomycota)

smut     
a disease caused by a smut fungus (Ustilaginomycotina) in the Basidiomycota or the fungus itself; it is characterized by masses of dark brown or black, dusty to greasy teliospores that generally accumulate in black, powdery sori

soft rot  
a softening, discoloration, and often disintegration of plant tissue as a result of fungal or bacterial infection

soil drench
an application of a solution or suspension of a chemical to the soil, especially application of a pesticide to manage soilborne pathogens

soilborne
carried on or beneath the soil surface

soil inhabitant
an organism that maintains its population in soil over an extended period of time

soil invader
an organism whose population in soil diminishes in several months to years

soil pasteurization
the process used to free soil of selected harmful microorganisms using heat

soil sterilization
the process used to free soil of all microorganisms

solarization  
a disease control practice in which soil is covered with polyethylene sheeting and exposed to sunlight, thereby heating the soil and inhibiting or killing soilborne plant pathogens

sooty mold   
the black, nonparasitic, superficial fungal growth on honeydew produced by aphids and other phloem-feeding insects

sorus   (pl. sori)  
a compact fruiting structure, especially the erumpent spore mass in the rust fungi (Pucciniales) and smut fungi (Ustilaginomycotina); occasionally a group of fruiting bodies as in Synchytriaceae; a cluster of sporangia on a fern sporophyte

sp. (abbr. for species; pl. spp.)
when a genus name is followed by sp., it means that the particular species is undetermined; spp. after a genus name means that several species are being referred to

species 
any one kind of life subordinate to a genus but above a race; a group of closely related individuals of the same ancestry, resembling one another in certain inherited characteristics of structure and behavior and relative stability in nature; the individuals of a species ordinarily interbreed freely and maintain themselves and their characteristics in nature

specific epithet
the second word in a Latin binomial

specific resistance
a resistance that is effective against some biotypes or races of the pathogen, but not others, usually inherited monogenically and expressed qualitatively. (see also vertical resistance) (contrasts with durable resistance, general resistance, horizontal resistance, race-nonspecific resistance)

spermagonium   (pl. spermagonia)    
a structure in which male reproductive cells are produced; in rust fungi, globose or flask-shaped haploid fruiting body composed of receptive hyphae and spermatia (pycniospores) (see also pycnium for rust fungi)

spermatium   (pl. spermatia) 
a male sex cell; a nonmotile male gamete; a haploid male gamete (see also pycniospore for rust fungi)

spicule    
a copulatory organ of a male nematode

spike
a botanical term for an unbranched inflorescence in which flowers (or spikelets of grasses) are attached directly, without petioles, to a central stem (e.g., wheat, gladiolus)

spikelet
a spikelike appendage composed of one or more reduced flowers and associated bracts; unit of inflorescence in grasses; a small spike

spiroplasma    
a spiral-shaped, plant-pathogenic mollicute (a prokaryote without cell wall)

spontaneous generation, theory of
the theory, now known to be invalid, that plants, animals, and microorganisms arise from nonliving materials under certain environmental conditions

sporangiophore    
a sporangium-bearing structure of a fungus

sporangiospore  
an asexual spore that is borne in a sporangium

sporangium   (pl. sporangia)    
a saclike structure in which the entire contents are converted into an indefinite number of asexual spores in certain fungi and funguslike organisms

spore     
a reproductive structure of fungi and some other organisms, containing one or more cells; a bacterial cell modified to survive an adverse environment

sporidium   (pl. sporidia)   
a basidiospore of rust fungi, smut fungi, and other members of Basidiomycota (the basidiomycetes)

sporocarp  
a spore-bearing fruiting body

sporodochium   (pl. sporodochia)    
a superficial, cushion-shaped asexual fruiting body consisting of a cluster of conidiophores

sporophore    
a spore-producing or spore-bearing structure such as a conidiophore, conidioma, ascoma/ascocarp, or basidioma/basidiocarp

sporophyte  
the diploid stage of a plant (contrasts with gametophyte)

sporulate    
to produce spores

spot  
a symptom of disease characterized by a limited necrotic area, as on leaves, flowers, and stems

springwood  
the part of the yearly xylem growth ring in woody plants formed early in the growing season, consisting typically of cells that are larger than those formed later in the season (contrasts with summerwood)

stabilizing selection
the theorized competitive disadvantage of unnecessary virulence genes; races with excess genes would have decreased fitness relative to races with fewer virulence genes, so a "super-race" would be less likely to appear in multiline crops

staghead
a defoliated, dead, or dying major branches in the crown of a tree, usually resulting from inadequate water uptake or translocation

stamen (adj. staminal)  
a male structure of a flower, composed of a pollen-bearing anther and a filament, or stalk

stele  
the central cylinder of vascular tissue (especially in roots)

stem pitting    
a disease symptom characterized by depressions on the stem

sterigma   (pl. sterigmata)    
a small, usually pointed projection that supports a spore

sterile
unable to reproduce sexually; free of living microorganisms

sterile fungus    
a fungus that is not known to produce any kind of spores

sterilization   (adj. sterilized)
the total destruction of living organisms by various means, including heat, chemicals, or irradiation

stigma  
the portion of a flower that receives pollen and on which the pollen germinates

stipe  
a stalk

stippling 
a series of small dots or speckles in which chlorophyll is absent

stipule
the small, leaflike appendage at the base of a leaf petiole, usually occurring in pairs

stolon 
a slender, horizontal stem that grows close to the soil surface; in fungi, a hypha that grows horizontally along the surface (see also runner)

stoma   (also stomate; pl. stomata; adj. stomatal)     
a structure composed of two guard cells and the opening between them in the epidermis of a leaf or stem, functioning in gas exchange

stone fruit
a fruit with a stony endocarp, e.g., cherry, peach, plum

strain 
a distinct form of an organism or virus within a species, differs from other forms of the species biologically, physically, or chemically

Stramenopila (Straminipila)
a kingdom including Oomycota (the oomycetes) along with brown and golden algae and diatoms. "Stramenopila" is the originally proposed spelling, whereas "Straminipila" has been proposed as more correct in form on the basis of the Latin root of the term

striate   (n. striations)  
marked with delicate lines, grooves, or ridges

stroma     (pl. stromata)       
a compact mass of mycelium (with or without host tissue) that supports fruiting bodies or in which fruiting bodies are embedded

stunting  
the reduction in height of a vertical axis resulting from a progressive reduction in the length of successive internodes or a decrease in their number

style  
the slender part of many pistils located between the stigma and the ovary and through which the pollen tube grows

stylet    
the stiff, slender, hollow feeding organ of plant-parasitic nematodes or sap-sucking insects, e.g., aphids and leafhoppers

stylet knob  
the structure at the base of a nematode stylet (see also basal knob)

stylet-borne transmission 
a type of virus transmission in which the virus is acquired and transmitted by the vector after short feeding times, and is retained by the vector for only a short period of time (see also nonpersistent transmission) (contrasts with circulative transmission, persistent transmission, propagative transmission)

suberize
to convert into cork tissue

subgenomic RNA
a piece of viral RNA, shorter than the entire genome of the virus, found in cells infected by the virus and sometimes encapsidated

subspecies
a subpopulation of a species, defined on the basis of more than one character (morphologic for many organisms) that distinguishes the members of the subpopulation from other members of that species

substrate 
the substance on which an organism lives or from which it obtains nutrients; chemical substance acted upon, often by an enzyme

sulfur dioxide (SO₂)  
a primary air pollutant produced in industrial processes and coal burning that causes interveinal necrosis on broadleaved plants and tip necrosis on conifers

summerwood
the part of the yearly xylem growth ring in woody plants formed late in the growing season and consisting of cells smaller than those of springwood (contrasts with springwood)

sunscald or sunburn  
the injury of plant tissues burned or scorched by direct sun

suppressive soil 
a soil in which various diseases are naturally at lower levels than expected due to biological factors in the soil; an example of natural biological control

suscept 
an abbreviated term for a susceptible plant

susceptible   (n. susceptibility)
prone to develop disease when infected by a particular pathogen (contrasts with resistant)

symbiosis   (adj. symbiotic; n. symbiont)
the living together of two different kinds of organisms that may, but does not necessarily, benefit each organism

sympodial
pertaining to proliferation of axes, in which each successive spore or branch develops behind and to one side of the previous apex, where growth has ceased

symptom 
an indication of disease by reaction of the host, e.g., canker, leaf spot, wilt (contrasts with sign)

symptomless carrier 
a plant that, although infected with a pathogen (usually a virus), produces no obvious symptoms

syncytium    (pl. syncytia)   
a multinucleate structure in root tissue formed by dissolution of common cell walls induced by secretions of certain sedentary plant-parasitic nematodes, e.g., cyst nematodes

synergism   (adj. synergistic)  
a greater-than-additive effect of interacting factors (contrasts with antagonism)

synnema   (pl. synnemata)    
compact or fused, generally upright conidiophores, with branches and spores forming a headlike structure (see also coremium)

systematics
the study of biological diversity and the evolutionary relationships between organisms

systemic    
pertaining to a disease in which the pathogen (or a single infection) spreads generally throughout the plant; pertaining to chemicals that spread internally through the plant

systemic acquired resistance (acronym SAR)
the reduced disease symptoms on a portion of a plant distant from the area where a hypersensitive response occurred or other stimulus was applied; a rapid and coordinated defense response against a variety of pathogens as a signal travels throughout the plant (see induced systemic resistance)

systemic fungicide
a fungicide that is absorbed into plant tissue and may offer some curative or after-infection activity; includes fungicides that are locally systemic, xylem-mobile (upward moving), and amphimobile (move in phloem upward as well as downward in the plant) (contrasts with contact fungicide, protectant fungicide)

T

taproot  
the primary root that grows vertically downward and from which smaller lateral roots branch

taxonomy (adj. taxonomic)
the science dealing with classifying organisms

teleomorph   
the sexual form in the life cycle of a fungus (see also perfect state) (contrasts with anamorph, holomorph, imperfect state)

telial host
the host plant on which a heteroecious rust fungus produces telia and, sometimes, uredinia (contrasts with aecial host)

teliospore     
a thick-walled resting or overwintering spore produced by the rust fungi (Puccininales) and smut fungi (Ustilaginomycotina) in which karyogamy occurs; it germinates to form a promycelium (basidium) in which meiosis occurs; teleutospore, teleutosporodesm 

telium   (pl. telia)   
a fruiting body (sorus) of a rust fungus that produces teliospores

temporary wilt
the wilting due to insufficient soil water from which a plant can recover when water is supplied

teratogen
a chemical that causes malformations in the fetus

testa (pl. testae)
the seed coat

thallus
the vegetative body of a fungus or a "simple plant," such as a moss

thatch  
the tightly intertwined layer of plant litter from accumulations of undecomposed or partially decomposed plant residues

thermotherapy
the use of heat to reduce or eliminate pathogens in plant tissue; often used on plants prior to meristem culture to produce pathogen-free plants

thorax  
the insect body part between the head and abdomen

tillage  
the process of turning or stirring the soil

tiller
a lateral shoot, culm, or stalk arising from a crown bud; common in grasses

tissue 
a group of cells, usually of similar structure, that perform the same or related functions

tissue culture
an in vitro method of propagating healthy cells from plant tissues

titer
the concentration of a virus

tolerance    (adj. tolerant)  
the ability of a plant to endure an infectious or noninfectious disease, adverse conditions, or chemical injury without serious damage or yield loss; in terms of pesticides, the amount of chemical residue legally permitted on an agricultural product entering commercial channels, usually measured in parts per million (ppm)

totipotency
the potential ability of a single cell to be regenerated into a whole organism because each nucleus contains the full genome

toxicity 
the capacity of a substance to interfere with the vital processes of an organism

toxin 
a poisonous substance of biological origin

tracheid  
an elongated conducting cell of the xylem, with tapering or oblique end walls and pitted walls

transcription  
the production of a complementary strand of RNA from a segment of DNA

transduction
the transfer of genes from one organism to another by viruses, especially in bacteria

transfer RNA (acronym tRNA)  
the RNA that moves amino acids to the ribosome to be placed in the order prescribed by the messenger RNA

transformation
the transfer of genetic materials from one organism to another by humans (genetic engineering); a means of genetic variation in bacteria by absorption and incorporation of DNA from another bacterial cell

transgenic  
possessing a gene from another species; used to describe the organisms that have been the subject of genetic engineering (see also genetically modified organism, GMO)

translation  
the assembling of amino acids into a protein using messenger RNA, ribosomes and transfer RNA

translocation 
the movement of water, nutrients, chemicals, or food materials within a plant

translucent
so clear that light may pass through

transmit (n. transmission)
to spread or transfer, as in spreading an infectious pathogen from plant to plant or from one plant generation to another

transpiration 
the loss of water by evaporation from leaf surfaces and through stomata

transposon
a piece of DNA capable of moving to a different location in the genome

trap crop
a crop planted around a field to protect the inner crop from diseases transmitted by aerial vectors; host crop of a parasitic plant, (e.g., witchweed, Striga spp.), that is planted to stimulate seed germination, and later sacrificed by plowing under before the parasitic plant produces new seeds

trenching  
the physical separation of soil in a vertical plane to sever grafted roots between trees

trichogyne
a female receptive hypha

trichome
a plant epidermal hair, of which several types exist

triplet codon  
a set of three nucleotide bases in DNA or RNA that code for an amino acid

tRNA (acronym for transfer RNA)  
the RNA that moves amino acids to the ribosome to be placed in the order prescribed by the messenger RNA

tuber  
an underground stem adapted for storage, typically produced at the end of a stolon

turgidity
a state of being rigid or swollen as a result of internal water pressure

tumor    
an abnormal swelling or localized outgrowth, often roughly spherical, produced by a plant as a result of attack by a fungus, bacterium, nematode, insect, or other organism (see also gall, knot)

tylosis    (pl. tyloses)    
a balloonlike extrusion of a parenchyma cell into the lumina of a contiguous vessel that partially or completely blocks it

type 
the example on which the description of a scientific name is based, and which fixes the application of the name (the type genus of a family, or the type species of a genus)

U

ultrastructure
the submicroscopic structure of a macromolecule, cell, or tissue

unicellular
one-celled (contrasts with multicellular)

uniflagellate
having one flagellum

unitunicate    
having a single ascus wall (contrasts with bitunicate)

uninucleate
having one nucleus (contrasts with multinucleate)

urediniospore     
the asexual, dikaryotic, often rust-colored spore of a rust fungus, produced in a structure called a uredinium; the "repeating stage" of a heteroecious rust fungus, i.e., capable of infecting the host species on which it is produced; urediospore, uredospore

uredinium   (also uredium; pl. uredinia)    
the fruiting body (sorus) of a rust fungus that produces urediniospores

V

vacuole
the generally spherical organelle within a plant cell, bound by a membrane and containing dissolved materials such as metabolic precursors, storage materials, or waste products

variegation  
a pattern of two or more colors in a plant part, as in a green and white leaf

variety   (adj. varietal)
a plant type within a species that is true to type and has recognizable characteristics, described by a third italicized word in a scientific name (see also cultivar)

vascular
pertaining to fluid-conducting (xylem and phloem) tissues in plants

vascular bundle  
a strand of conductive tissue, usually composed of xylem and phloem (in leaves, small bundles are called veins)

vascular cambium 
a cylinder of meristematic cells (lateral meristem) that produces secondary phloem to the outside and secondary xylem (wood) to the inside of a branch or trunk of a woody plant

vascular cylinder  
the cylinder of vascular tissue in stems or roots (see also stele)

vascular wilt disease  
a disease of the xylem that disrupts the normal uptake of water and minerals, resulting in wilting and yellowing of foliage

vector 
a living organism (e.g., insect, mite, bird, higher animal, nematode, parasitic plant, human) able to carry and transmit a pathogen and disseminate disease; in genetic engineering, a vector or cloning vehicle is a self-replicating DNA molecule, such as a plasmid or virus, used to introduce a fragment of foreign DNA into a host cell

vegetative 
referring to somatic or asexual parts of a plant that are not involved in sexual reproduction

vegetative propagation
a form of asexual reproduction in plants in which cuttings, bulbs, tubers, and other vegetative plant parts are used to grow new plants

vein  
a small vascular bundle in a leaf

vein banding  
a symptom of virus disease in which regions along veins are either darker green or distinctly more yellow than tissue between veins

vein clearing
the disappearance of green color in or around leaf veins

vermiform  
worm-shaped

vertical resistance 
a resistance that is effective against some biotypes or races of the pathogen, but not others, usually inherited monogenically and expressed qualitatively (see also specific resistance) (contrasts with general resistance, horizontal resistance, race- nonspecific resistance)

Vertifolia effect
the loss of general (durable, horizontal, host-nonspecific) resistance in a cultivar after several generations of selection during which a major gene confers resistance to the dominant race or biotype of the pathogen; first observed in the potato cultivar Vertifolia with late blight resistance

vesicle   
a thin sac in which zoospores are differentiated and released; the bulbous head terminating the conidiophores of Aspergillus; structure formed by endomycorrhizal fungi within living cells of the root

vessel   
a water-conducting structure of xylem tissue with openings in end walls

viable (n. viability)
the state of being alive; able to germinate, as seeds, fungal spores, sclerotia, etc.; capable of growth

virescence (adj. virescent)    
a state or condition in which normally white or colored tissues (e.g., flower petals) become green

virion    
a complete virus particle

viroid 
an infectious, nonencapsidated (naked) circular, single-stranded RNA

viroplasm
the cellular inclusions that are sites of synthesis of viral components and the assembly of virus particles

virulence 
a degree or measure of pathogenicity; the relative capacity to cause disease

virulent 
highly pathogenic; having the capacity to cause severe disease (contrasts with avirulent)

viruliferous 
virus-laden, usually applied to insects or nematodes as vectors

virus     
a submicroscopic, intracellular, obligate parasite consisting of a core of infectious nucleic acid (either RNA or DNA) usually surrounded by a protein coat

viscin  
the sticky tissue produced on the seed coat of parasitic flowering plants in the Viscaceae mistletoes) that helps attach the seed to the host plant branch

volunteer
a self-set plant; a plant seeded by chance

vulva    
the exterior opening of a mature female nematode's reproductive system