Classification of Plant Pathogens - Westcott's Plant Disease - page 27

Classification in accordance with convention or law is called taxonomy .
Common names vary from locality to locality and country to country. Scien-
tific names are international and are based on the binomial system. Each kind
of bacterium, fungus, nematode, or higher plant is a species, and it has two
Latin words for its name. The first name indicates the genus to which the
species belongs, and the second the species itself. The latter name is usually
descriptive. Diplocarpon rosae means that Diplocarpon , the blackspot fun-
gus, is found on rose. Sometimes the species name honors a person, as
Coniothyrium wernsdorffiae for the fungus causing brand canker of rose.
Such a species name, derived from a proper name, has sometimes been
written with a capital, but present custom is to decapitalize all species
names. The names of genera should always be written with a capital.
Correctly, the author of the name should be written after the species. Then,
if someone else places the species in a new genus, the name of the first author
is put in parentheses followed by the name of the second author. When
a number of taxonomists have worked on a group, the list of authors gets
quite unwieldy. For simplicity all authors have been omitted from the scien-
tific names in this text. The correct name for a fungus with more than one
stage is that first given, with a valid description, for the teleomorph or sexual
stage. That rule is followed here with a few exceptions-as when a fungus is
almost universally recognized by another name.
Species are grouped into genera, related genera into families, designated
with the suffix aceae , as Erysiphaceae, and families into orders with the suffix
ales , as Erysiphales. Groups of related orders form classes.
Strange as it may seem, scientists are not yet agreed on what constitutes
a plant or even a living organism. The old definition of bacteria as unicellular
plants is disputed, and some question if fungi are truly plants. Bacteria are
prokaryotes. Prokaryotes are generally single-celled microorganisms that
have a cell membrane or a cell membrane and a cell wall surrounding the
cytoplasm and no organized nucleus. Eukaryotes contain membrane-bound
nuclei, mitochondria and - in plants only - chloroplasts. Although viruses are
known to multiply inside their hosts or vectors, the question of their being
a living entity has not been resolved. The arguments continue. Meanwhile
entities have to be grouped into some sort of order. Whittaker in 1969
introduced the five kingdom classification for all living organisms: Monera
(or Procaryota), Protista, Animalia, Plantae and Fungi (or Mycota). The
Monera are organisms with small cells lacking nuclei, mitochondria and
plastids, viz. the bacteria. The Protista include Microorganisms with one-
celled, often motile thalli (cells contain nuclei). The plants, animals and fungi
are believed to have evolved from Protista. The Fungi are characterized as
heterotrophic organisms, dependent on organic food, which they absorb. The
following scheme, adapted from the Plant Pathogenic Fungi , Nova Hedwigia
87: 288 pp. by J. A. von Arx, is an attempt to show the position of fungal plant
pathogens in the Kingdom Mycota. The listing of families is restricted to
those containing such pathogens.