Biology Reference
In-Depth Information
Wilt Diseases
To wilt means to lose freshness or to become
flaccid. Wilting in plants may be temporary, due
to too rapid transpiration; or it may be perma-
nent, due to continued loss of water beyond the
recovery point. Disease organisms, by reducing
or inhibiting water conduction, may cause per-
manent wilting. Because wilt diseases are sys-
temic, and tied up with the entire vascular
system of a plant, they are usually more impor-
tant, and harder to control, than localized spots
or cankers. In many cases the fungus enters the
plant from the soil through wounds or root
hairs and cannot be controlled by protective
spraying. Often, although the fungus is present
only near the base of a plant, the first symptom is
a flagging or wilting or yellowing of a branch
near the top. Many species of
Fusarium
are
responsible for important wilts and “yellows.”
Verticillium
is a common cause of wilt in
maples, other trees, and shrubs, but most impor-
tant among the wilt pathogens are two species of
Ceratocystis
, one causing oak wilt, the other
Dutch elm disease.
central Tennessee. Spread is rapid and death
quick. First notice of the disease was in Tennes-
see in 1933. By 1938 only 5 % of the persimmons
in the infected stand were alive. Topmost
branches wilt suddenly, then the rest of the tree,
with defoliation and death. The fungus fruits in
salmon-colored spore masses in cracks in dead
bark of dying trees or under bark of dead rings.
Fine, blackish streaks are present in five or six
outer rings of trunk, branches, and roots.
No control is known.
Cephalosporium diospyri
Acremonium
diospyri
).
Persimmon Wilt
, a lethal disease of
common persimmon.
Cephalosporium sp
Sunflower wilt
.
(see
▶
Ophiostoma (Ceratocystis)
Ascomycetes, Ophiostomatales
Perithecia enlarged at base, with thin walls, and
long slender neck, ascus wall evanescent, asco-
spores hyaline. Conidial stage may be
Chalara
with endogeneous spores or
Graphium
with
external conidia or conidiophores united into
a dark stalk (synnema).
Ceratocystis fagacearum (
Chalara quercina,
Endoconidiophora fagacearum
).
Oak Wilt
, our
most serious disease of oaks, now known in
20 states from Texas and Oklahoma east to Penn-
sylvania and South Carolina. It has also been
reported in Florida. Although apparently present
in the Upper Mississippi Valley for many years,
Acremonium (Cephalosporium)
Leaf Spots
.
Acremonium diospyri (formerly
Cephalosporium diospyri
).
Persimmon Wilt
,
a lethal disease of common persimmon. Wilt
appears in scattered localities from North Caro-
lina to Florida and west to Oklahoma and Texas,
but most infection is in north central Florida and
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