DISEASES OF ROOTS MIGRATORY ECTOPARASITES

DISEASES OF ROOTS
SEDENTARY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Tylenchulidae
Tylenchulus
Tylenchulus semipenetrans = Citrus Nematode
= major citrus pathogen throughout the world
Causes “Slow Decline”
Also important on grape, olive, persimmon

*
Agrios

Tylenchulus semipenetrans = citrus nematode
2.
Nematode molts
3 times to become
an adult
3.
Posterior remains
in soil and female
swells with eggs
1.
J2 infective
penetrate outer
layers of cortex
Van Gundy & Kirkpatrick

Tylenchulus semipenetrans – Citrus Nematode
Anterior elongates, penetrates deep into cortex,
becomes irregularly shaped and fills shape of cells
R.S. Hussey
Nemapix 1
J.D. Eisenback
Nemapix 1

Tylenchulus semipenetrans – Citrus Nematode
Female feeds and destroys
cells, leaving space for
head to move around
6-10 nurse cells form
in cortex, do not enlarge
APS Slide Set #20

Tylenchulus semipenetrans – Citrus Nematode
Males remain motile in soil to
mate with females but males
are not required for
reproduction.
Some males reportedly do not
feed either as juveniles or as
adults and have reduced
stylet and esophagus.
Nemaplex
U.C. Davis
Nematology

Tylenchulus semipenetrans – Citrus Nematode
Eggs are deposited in a gelatinous matrix in the soil.
Life cycle is completed in 9 weeks.
Feeder roots look encrusted due to
sand embedded in gelatinous matrix
(= sign not symptom).
U.C. Nematology
Nemapix 2

Tylenchulus semipenetrans – Citrus Nematode
Development of J2 stops if host is not present.
J2 can persist in soil for years
until host is present.
Nemaplex
U.C. Davis
Nematology

Tylenchulus semipenetrans – Citrus Nematode
Symptoms of “Slow Decline”
- Tissue damage per individual is not great.
- Problem is with high populations
(500+/g soil and roots = 100+/cm root length)
- Small feeder roots do not develop properly which
causes slow decline.
- Plants can't get enough nutrients or water.
- Nurse cells eventually break down and allow
microorganisms to invade = increased necrosis.

Tylenchulus semipenetrans – Citrus Nematode
“Slow Decline”
J.W. Noling

Tylenchulus semipenetrans – Citrus Nematode
Symptoms of “Slow Decline”
Foliage sparse, often dull gray-green or bronze-green,
leaves smaller than normal, upright and cupped.
New growth is reduced.
Fruit set reduced,
smaller than normal.
Trees wilt often
during midday.
C. Overstreet
Nemapix 1

http://www.plantprotection.hu/modulok/angol/citrus/citrus_images/

Tylenchulus semipenetrans – Citrus Nematode
Symptoms of “Slow Decline”
- Disease is severely influenced by soil and nutrient
conditions.
- Soils with 10-15% clay are worse (?) than those with
either more or less clay.
=> sandy soils favor the nematodes but damage is
worse in soils that stay more wet.
Nematodes do not do well in heavy soils.
- Nematodes are more damaging when calcium, sodium,
or potassium are in short supply.

Tylenchulus semipenetrans – Citrus Nematode
Control
- Sanitation to protect against introduction of
nematode.
- Hot water (45 C for 2 minutes) and nematicide dips
of bare rooted seedlings.
- Genetic resistance by grafting desirable varieties to
resistant rootstocks.

Tylenchulus semipenetrans – Citrus Nematode
Chemical control as a preplant treatment and/or in
drenches of living trees.
Periodic application through drip irrigation system.
Untreated
Nematicide treated
Treatments have resulted in 5X increases in yield.

DISEASES OF ROOTS
SEDENTARY ECTOPARASITES
CLASS CHROMADOREA
Order Rhabditida
Suborder Tylenchina
Infraorder Tylenchomorpha
Family Hoplolaimidae
Rotylenchulus
Rotylenchulus reniformis = Reniform Nematode
Important to many crops in warm climates.
Cotton, tomato, soybean, sweet potato, pineapple, etc.

*
Agrios

Rotylenchulus reniformis – Reniform Nematode
Young female is infective.
Penetrates anywhere
on root
Stimulus from root
needed for final molt
Head pushes
through to
endodermal
cells
J2 molt 3 times
without feeding,
into immature
males and females
C. Overstreet

Rotylenchulus reniformis – Reniform Nematode
J2 molt 3 times without
feeding, develop into
immature males and females.
Young females are infective
stage, males remain in soil.
E.C. McGawley
Nemapix 1

Rotylenchulus reniformis – Reniform Nematode
Nematode pushes through
cortex cells until its head
rests in endodermal cell.
R.S. Hussey
Nemapix 1

Rotylenchulus reniformis – Reniform Nematode
Female becomes sedentary and the feeding site develops into a
syncytium of 5-10 interconnected, and usually enlarged pericycle
cells.
R.V. Rebois
Nemapix 1

Rotylenchulus reniformis – Reniform Nematode
Life cycle is completed
in 3-4 weeks.
Populations may reach
10,000/100 cc soil!
Kidney-shaped reniform nematode
U. Zunke
Nemapix 2

Rotylenchulus reniformis – Reniform Nematode
C. Overstreet
Nemapix 1
Females lay eggs into large
gelatinous matrix.
Sand grains adhere to
Matrix and serve as a sign
of infection.

Rotylenchulus reniformis – Reniform Nematode
Symptoms
- Infected plants have reduced levels of nitrogen,
potassium, and manganese and exhibit these nutrient
deficiencies.
- Inadequate root function due to root damage results
in leaf tissues with compact, small cells.
- Smaller leaves reflect less light than healthy leaves
and allows for large areas to be assessed for damage
with remote sensing.

Rotylenchulus reniformis – Reniform Nematode
Feeding damage to banana rhizomes
Sambasivam

Rotylenchulus reniformis – Reniform Nematode
Six Untreated Rows of Cotton
C. Overstreet
Nemapix 1

Rotylenchulus reniformis – Reniform Nematode
Symptoms – Pineapple
E.C. McGawley
Nemapix 1

Rotylenchulus reniformis – Reniform Nematode
Control
- Resistant varieties of soybean have been developed.
- Some legumes, grasses and sugarcane do not support
reproduction and can be used in crop rotation.
- Chemical nematicides