Symptoms and Signs of Plant
of Plant Disease
Plant mortality (death) of
an entire plant such as
Necrosis can also occur on plant parts
such as needles (left) or parts of plants like the leafspots
on river birch (middle) or the necrotic areas
on leaflets of green ash (right).
Discrete or localized
necrotic area, such as those seen on this
The localized death of woody
plant tissue usually resulting in
a collapsing of the bark and
Cankers can be formed from callus tissue,
seen as concentric ridges on
the black walnut (above), which is often
formed by the plant in an attempt to
limit spread of the pathogen. In some instances
the plant does not have the ability to form callus tissue as seen
on the redbud to the right.
Browning or darkening, seen in the cross-sections
sycamore, that is indicative of dead cells.
Rapid necrosis of a plant or plant parts
as seen in this slide of pear.
The blackened leaves and twigs developed
in a relatively short
period of time (several days to a few weeks).
Necrosis of terminal portions of the crown
and proceeding toward the trunk
as seen on this oak (left). In some instances
such as the pine (center and
right), only the terminal dies back.
Necrosis of plant cells involved in water
transport, thus depriving
foliage of adequate water and causing
loss of turgor pressure.
Necrosis of plant chloroplasts resulting
in a yellow appearance as seen
on the foliage of the river birch near D.H.
Hill Library. Note that there is
a second symptom on the chlorotic birch leaves.
Chlorosis on pine needles.
Wood decay involves disintegration of dead
woody plant cells and is technically not a disease. However, since decay
destroys the most valuable part of a tree (wood), it is discussed in some
detail in this course.
Atrophy or hypoplasia involves the slowing
down or retardation of normal plant
processes resulting in a stunting of the
entire plant or plant parts. Note the size
difference and the shoot and needle growth
difference in the pines (left)
(chlorosis is also evident) and the size
of the cones (right).
Chlorosis also can result from the inhibition
or retardation of chloroplast function and
development. This condition also can be noted
on the white pine in the previous
slide. Note the yellow (chlorotic) areas
around the leafspot on this river birch.
Hypertrophy and Hyperplasia
Abnormal increase in cell size.
Abnormal increase in cell numbers.
These conditions frequently occur together
and cannot be distinguished without a microscope. Both conditions, separately
and together, can cause overgrowths of a plant part or an area on a plant.
Terms used to describe this symptom:
Note the chlorosis on the blisters.
Signs are any physical or direct evidence
of a disease-causing agent discernable with
the unaided eye. This limits signs chiefly
to those agents such as some fungi, nematodes
and parasitic plants that produce macroscopic
structures. This photo on the right shows
mycelium and mycelial strands growing from
a diseased root.
Black mycelium growing on needles and twigs
of white pine.
Mycelial fan (the grey area at the base)
growing under the bark of an infected yellow birch.
These small round structures are sclerotia
of a fungal pathogen and are frequently produced by certain fungi.
Black shoe-string like structures are rhizomorphs.
Most signs of fungal pathogens are reproductive
structures such as these basidiocarps (mushrooms) growing from
the base of an oak.
Basidiocarps (conks or brackets) of a
wood decay fungus on a
southern red oak (left) and an oak branch
Apothecia (reproductive structures of
a certain class of fungi) growing on a
Spore masses of a fungus growing on a
Perithecia (reproductive structures of
a another class of fungi) growing on
an elm leaf; red perithecia on a canker on
a black walnut tree.
Spore horns of a fungus that
attacks red cedar.
Spore tendrils of a fungus
growing on red cedar needles.
Yellow-orange blister-like spore-bearing
structures termed aecia of a fungus on pine.
The yellowish structures growing on this
ponderosa pine are shoots of a
dwarf mistletoe plant that
is parasitizing the pine.
The greenish-yellow structures growing on
this oak are shoots of
the parasitic higher plant true mistletoe
or leafy mistletoe.
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This website was prepared by Becky Bernard.
Last updated 04 February 2008 by M.J. Munster