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SCN:
SCN Basics
SCN Life Cycle
SCN Life cycle pictures
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SCN Invasion (pictures!
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2 day
4 day
6 day
8 day SCN databases
SCN gene database
SCN genes of interest
Soybean cv SCN race
Soybean Defense Response
Defense
Response overview
Thru
the microscope
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microarray database
Soybean gene database
R genes
R gene overview
Rhg
mapping
Rhg1
Rhg4
Hypersensitive response
Oxidative
burst
Systemic Acquired
Resistance
Pathways
Jasmonic acid
Salicylic acid
Secondary products
Ethylene
Sucrose & Trehalose
Genes/enzymes
peroxidase
copper amine oxidase
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Life Cycle of SCN
The first report of the soybean cyst nematode
IHeterodera glycines Ichinohe, was in Japan in 1915 and is a sedentary
endoparasitic nematode. The life cycle of SCN consists of four
stages which are separated by molts. During the molts the cuticle
is replaced. The first molt
occurs while the nematode is still inside the egg. The
second stage juvenile (J2) is motile and is infective, penetrating the root
and migrating to its feeding site.
Nematodes secrete cellulase in the saliva from the secretory
granules of the subventral gland and use mechanical force to migrate
through the root. Second-stage juveniles penetrate the epidermis and migrate into
the root, cutting through successive cells, through the
cortex toward the vascular cylinder.
The cellular damage usually causes necrosis along the migration
path of the nematode. The nematode completely alters its behavior when it
arrives at suitable cells for feeding, where it gently pierces the initial
syncytial cell and injects saliva into the cytoplasm. The cell is
usually a procambial cell near the primary xylem.
The second-stage juveniles induce specialized feeding cells.
called syncytia. Multinucleate syncytia are produced from protoplasts of
procambial cells after partial dissolution of the cell wall; the nuclei
are hypertrophied at two days after infection. An electron dense
"feeding plug" is formed around the stylet to form a seal when
the stylet is removed. The nematode also makes a feeding tube
which allows molecules of about 40kDa and less pass into the nematode.The nematodes become sedentary then undergo three molts during
their development to the adult stage.
In the root the number of males increase under crowding or poor nutrition. Males feed until the end of the J3 stage, then become mobile
again. Syncytia have high metabolic activity, with hypertrophied
nuclei, increased cytoplasmic density and increased cell organelles.
Smooth and rough endoplasmic reticulum accumulate in the
thick-walled initial syncytial cell.
Nematode secretions are surrounded by a narrow region of
endoplasmic reticulum that integrates with the rough endoplasmic
reticulum of the host cytoplasm. Initial syncytial cell and adjacent cells show
slight enlargement at 18 hrs and have definite disruptions in their
connecting cell walls.
The third and fourth molts of the female occur as
the female feeds. At around thirty days after invasion, the female has
produced 200 to 600 eggs, some of which are extruded in a gelatinous
mass, while most are retained. The outer integument of the female
begins to harden and protect the encapsulated eggs, keeping them viable
in soil for up to nine years.
Refs:
Biology and Management of the soybean c, especially
LD Young Ch. 3. pp 27-36; and BY Endo. Ch. 4. pp.37-49
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