Glossary - Westcott's Plant Disease - page 696

Physiologic Races . Pathogens of same variety
and species structurally the same but differing
in physiological behavior, especially in ability
to parasitize a given host.
Phytopathology . Plant pathology, science of
plant disease.
Phytoplasma . A MLO that

Sclerotium , pl. Sclerotia . Resting mass of fungus
tissue, often more or less spherical, normally
having no spores in or on it (Fig. 7, p. 332;
Fig. 9, p. 335).
Scorch . Burning of tissue, from infection or
weather conditions.
Scutellum . Plate or is pathogenic to shieldlike cover, as in

plants.
Pileus . Hymenium-supporting part of a fruit body
of a higher fungus; the cap of a mushroom.
Primary Infection . First infection by a pathogen
after going through a resting or dormant
period.
Prokaryotic . Organisms which lack a true
nucleus; includes bacteria and mycoplasmalike
organisms.
Promycelium . Basidium of rusts and smuts.
Pulvinate . Cushionlike in form.
Pycnidium , pl. Pycnidia . Flasklike fruiting body
containing conidia.
Pycnium . Spermagonium in the rusts, the 0 stage,
resembling a pycnidium (Fig. 2, p. 349).
Resistance . Ability of a host plant to suppress or
retard activity of a pathogen.
Resting Spore . A spore, often thick-walled, that
can remain alive in a dormant condition for
some time, later germinating and capable of
initiating infection.
Resupinate . Flat on the substratum with hyme-
nium on outer side.
Rhizoid . Rootlike structure (Fig. 2, p. 36).
Rhizomorph . A cordlike strand of fungus hyphae.
Ring Spot . Disease symptoms characterized by
yellowish or necrotic rings with green tissue
inside the ring, as in virus diseases.
Roguing . Removal of undesired individual plants.
Rosette . Disease symptom with stems shortened
to produce a bunchy growth habit.
Russet . Brownish roughened areas on skins of
fruit, from abnormal production of cork
caused by disease, insect, or spray injury.
Rust . A fungus, one of the Uredinales, causing
a disease also known as rust.
Saprophyte . An organism that feeds on lifeless
organic matter.
Scab . Crustlike disease lesion; or a disease
in which scabs are prominent symptoms
(Fig. 1, p. 366).

Microthyriales.
Septate . Having cross-walls, septa.
Sessile . Having no stem.
Seta , pl. Setae . A stiff hair, or bristle, generally
dark-colored.
Shothole . A disease symptom in which small
round fragments drop out of leaves, making
them look as if riddled by shot.
Sign . Any indication of disease other than
reaction of the host plant - pores, mycelium,
exudate, or fruiting bodies of the pathogen.
Slurry . Thick suspension of chemical; used for
seed treatment.
Smut . A fungus of the Ustilaginales, characterized
by sooty spore masses; the name also used for
the disease caused by the smut.
Sooty Mold . Dark fungus growing in insect
honeydew.
Sorus , pl. Sori . Fungus spore mass, especially of
rusts and smuts; occasionally, a group of
fruiting bodies.
Species . One sort of plant or animal; abbreviated
as “sp.” singular, and “spp.” plural. A genus
name followed by sp. means that the particular
species is undetermined. Spp. following
a genus name means that several species are
grouped

together without being named

individually.
Spermagonium . Walled structure

in which

spermatia are produced, a pycnium.
Spermatium ,pl. Spermatia , a sex cell (+ or

),

a pycniospore.
Sporangiole . Small sporangium without
a columella and with a small number of
spores.
Sporangiophore . Hypha bearing a sporangium.
Sporangium . Organ producing nonsexual spores
in a more or less spherical wall (Fig. 1, p. 35).
Spore . A single-to many-celled reproductive
body, in the fungi and lower plants, which
can develop a new plant.