Each entry consists of a term (in bold), a definition of the term, and a number in parentheses (0) indicating the source of the definition. Clicking on the speaker icon will give you the pronunciation of the term. (Be sure to close the window for the sound player after each use.) The pencil icon will give you a drawing, and the camera icon will give you a photograph.
race.
A subspecies group of pathogens that infect a given set of plant varieties.
(2)
rachis.
In fungi: A conidiophore elongating to one side of a terminally produced spore,
often resulting in a zig-zag-shaped structure.
(22)
range.
Of a plant pathogen: The geographical region or regions in
which it is known to occur.
(20)
recombinant DNA.
DNA molecules in which sequences, not normally
contiguous, have been placed next to each other by in vitro methods.
(10)
rectum.
In nematodes: Posterior gut of the female. A narrow, dorsoventrally flattened
tube that is lined with cuticle and separated from the intestine by a sphincter
muscle.
(14)
reflexed.
Bent back.
(14)
REMI.
Restriction enzyme mediated integration.
A method of transformation that generates tagged mutations.
(19)
reniform.
Kidney-shaped.
(14)
replicon.
Any DNA sequence or molecule that possesses a replication
origin and is therefore potentially capable of being replicated in
a suitable cell.
(16)
resistance.
The ability of an organism to exclude or overcome, completely
or in some degree, the effect of a pathogen or other damaging factor.
(2)
resistant.
Possessing resitance.
(3)
response.
The change produced in an organism by a stimulus.
(20)
resting spore.
A thick-walled spore, particularly one formed by a
sexual process, germinating only after an extended period of dormancy
(e.g., an overwintering teliospore).
(16)
restriction endonuclease.
An endonuclease that binds to double-stranded DNA at
a specific nucleotide sequence and then, if both strands of the DNA lack
appropriate modification at that sequence, cleaves the DNA either at the
recognition sequence or at another site in the DNA molecule.
(16)
reticulate.
Having net-like markings.
(14)
retrorse.
In a backward or downward direction.
(14)
revolute.
Of the margin of the pileus: rolled back or up.
(17)
RFLP.
Restriction fragment length polymorphism.
Inherited differences in sites for restriction enzymes (e.g., caused by base
changes in the target site) that result in differences in the lengths of
the fragments produced by cleavage with the relevant restriction enzyme.
RFLPs are used for genetic mapping to link the genome directly to a conventional
genetic marker.
(13)
rhabdions.
In nematodes: Plates in the cuticular lining of the
stoma that make up
the walls of the various divisions of the stoma.
(14)
rhizoid.
A root-like structure forming part of the thallus in
certain algae and fungi; it may anchor the organism to the substratum and/or
act as an absorptive organ.
(16)
rhizomorph.
A macroscopic, typically rope-like strand of
compacted tissue formed by certain higher fungi. Rhizomorphs often are enduring
structures that can remain dormant under adverse conditions.
(22)
rhizomycelium.
Branching, anucleate or sparsely nucleate, rhizoidal filaments
of variable width forming part of the thallus in some fungi.
(Pl. rhizomycelia.)
(16)
rhizoplane.
The root surface.
(16)
rhizosphere.
An environment regarded, variously, as (a) that region
of the soil modified as a result of the uptake and deposition of
substances by a growing root, (b) the root itself, together with that volume
of soil which it influences, (c) the root surface together with that region
of the surrounding soil in which the microbial population is affected by
the presence of a root.
(16)
Rickettsiae.
Microorganisms similar to bacteria in most respects but
generally capable of multiplying only inside living host cells; parasitic
or symbiotic.
(2)
ringspot.
A type of local lesion consisting of single or concentric
rings of discoloration or necrosis, the regions between the concentric rings
being green. The center of the lesion may be chlorotic or necrotic.
(16)
RNA blotting.
A technique for transferring RNA from an agarose gel to a nitrocellulose
filter on which it can be hybridized to a complementary DNA.
(13)
roestelium.
In the Uredinales an aecium with a
cornute peridium,
thin at the sides, usually rupturing by longitudinal slits, and made up of
characteristically marked and imbricated cells. The name is taken from the
form-genus Roestelia.
(Pl. roestelia.)
(17)
rogue.
A variation from the standard varietal type; also, to remove
such undesirable plants (especially those infected with viruses) from the
growing crop.
(20)
roguing.
The removal of diseased plants from a crop in order to prevent
the spread of the disease.
(16)
rosette.
An abnormal condition in which the leaves form a radial cluster
on the stem.
(16)
rot.
The softening, discoloration, and often disintegration of a succulent
plant tissue as a result of fungal or bacterial infection.
(2)
roundworm.
Nematode.
(20)
rugose.
Wrinkled.
(14)
russet.
Brownish, roughened areas on the skin of fruit as a result of cork formation.
(2)
rust.
1. Fungus of the class Urediniomycetes. 2. Any of various plant
diseases caused by members of the Urediniomycetes or by species of
Albugo. The diseases are called "rusts" because many of
the causal agents form rust-colored spores on affected plants.
(16)