A N I NTRODUCTION TO P LANT
D ISEASES , PART III-N EMATODES ,
V IRUSES AND A BIOTIC FACTORS
N EMATODES

Nematodes are non‐segmented roundworms

About 10% are plant pathogens
l
h

All plant parasitic nematodes have a mouthpart called a stylet
t l t
Pinewood nematode
N EMATODE D ISEASES

Root knot

Foliar nematode leaf spots

Pine wilt disease

Sting nematode damage on Sting
nematode damage on
turf
R ING N EMATODE
Plant parasitic nematodes have a mouthpart called a stylet. They use it to rupture cell walls and feed
walls and feed on the content of the cell.
stylet
Stylet
F OLIAR
N EMATODE /B RUNNERA
 Foliar nematodes F li
d
feed on the leaves of plants
 Lesions are angular
 These nematodes move from the soil to foliage in a film of water and
of water and enter through stomata
Foliar nematode
emerging from leaf
tissue
R OOT
KNOT
N EMA
DAMAGE
Female root knot nematode
R OOT KNOT N EMATODE
Nematodes in a slice from a root gall; nemas on right stained with acid fuschin
P INE W ILT
•Longhorn b tl
beetles carrying i
nematodes attack susceptible pines.
•Nematodes plug up the vascular system
vascular system causing the tree to wilt, needles to turn brown and tree soon dies.
Nematode detection
Soil assays and microscopic examination is the only reliable way to determine if nematodes are a problem.
P LANT V IRUSES

IInfectious, submicroscopic, intracellular f ti
b i
i i t
ll l
agent

Composed of nucleic acid and a protein coat

Tobacco mosaic virus was the first described

Most plant viruses are named for the first plant in which they were found (or for an
plant in which they were found (or for an economically important host)

Nearly 1 000 species of plant viruses
Nearly 1,000 species of plant viruses
H OW
DO
V IRUSES
SPREAD
P LANT TO P LANT ?

Insects (cucumber mosaic virus –
aphids; tomato spotted wilt virus, impatiens necrotic spot virus‐
thrips)

Nematodes (tobacco rattle virus)

Mites (rose rosette virus)

Sap (tobacco mosaic virus)
Sap (tobacco mosaic virus)

Fungi (soil‐borne mosaic)
S YMPTOMS OF V IRUS DISEASES
Variety of symptoms
symptoms including: mosaic, mosaic,
ringspots, oakleaf
patterns, stunting, fl
flower break
b k
M OSAIC VIRUS SYMPTOM
Mosaic
Mosaic symptoms of plants are not caused by one virus, but multiple viruses such as: tobacco mosaic virus
mosaic virus, cucumber mosaic virus, alfalfa mosaic virus, etc.
V IRAL S YMPTOMS
Several plant virus cause ringspots
symptoms on leaves and/or fruit. Two of the most common are: tomato spotted wilt virus and
virus and impatiens necrotic spot virus.
Line pattern or oak leaf pattern
Ringspots
C ANNA Y ELLOW M OTTLE
V IRUS
Infected canna is stunted and variegation is not true to type compared to healthy canna on
healthy canna on right.
R OSE ROSETTE
Rose rosette virus causes a witches broom (rosette) symptom; symptom;
infected plants die within 2‐3 years. Many roses are susceptible. Eriophyid mites are vectors of
are vectors of the virus.
F LOWER B REAK
Tulips infected with viruses may have petals with
petals with streaks of bright colors. This is called “flower break” .
T ULIPMANIA (H OLLAND 17 TH
C ENTURY )

A single prized tulip bulb with streak A
single prized tulip bulb with streak
symptoms was traded for:

4 tons of wheat, 8 tons of rye
4 tons of wheat, 8 tons of rye

2 tons of butter, 1,000 lbs of cheese

4 tons of beer, 2 barrels of wine

4 oxen, 8 pigs,12 sheep

A suit of clothes, a bed and silver drinking cup

By 1637, the tulip market had crashed with the economy
PARASITIC F LOWERING
P LANTS

Certain flowering plants are parasites of other plants
of other plants

Do not have root systems, but structures that absorb water, minerals and sugars from their host

Examples: leafy mistletoe, dwarf mistletoe, dodder, witchweed, broomrape
L EAFY M ISTLETOE
P HORADENDRON SP.
Mistletoes are dioecious, having distinct male and female plants. Leafy plants Leaf
mistletoe is a hemiparasite, producing its food via photo‐
synthesis, but absorbing water and minerals
and minerals from their host.
D ODDER
C USCUTA SP.
Dodder seed germinate; when dodder comes into contact with a host stem, it a host stem it
loses contact with the ground. Dodder is a holo‐
parasite, that is totally dependent upon its host for food
its host for food.
S QUAW R OOT
C ONOPHOLIS AMERICANA
Conopholis is a perennial, non‐
photosynthesizi
ng parasitic plant that plant that
attacks the roots of trees such as oak and beech.
L ICHENS
ARE
N OT P LANT
PARASITES
Lichens are fungi that have discovered agriculture. Trevor Goward, Lichenologist.
Lichens are comprised of fungi that have formed a symbiotic symbiotic
relationship with algae or cyanobacteria
(f
(formerly called l
ll d
blue‐green algae).
D ISEASES

CAUSED BY ABIOTIC
FACTORS
E i
Environmental factors
t lf t

Temperature

Moisture

Light
Li ht

Nutrients

pH

Chemicals‐
Ch
i l air pollutants, i
ll t t
herbicides
I RON CHLOROSIS
Iron chlorosis of willow oak caused by alkaline soil pH
WATER S TRESS
Leaf scorch
due to
drought
g
stress/
dogwood
CAN LEAD TO
LEAF SCORCH
I NJURY TO P LANTS
Injury to plants is more immediate and not progressive over
progressive over time as many abiotic problems like nutritional deficiencies.
Pictured right are hail damage to dogwood and
dogwood and yellow bellied sapsucker injury to sugar maple.
F URTHER R EADING

EEssential Plant Pathology ‐
ti l Pl t P th l
S h
Schuman and D’Arcy

Plant Pathology ‐ Agrios

Plant Pathology Concepts ‐
gy
p Trigiano, g
,
Windham and Windham