Lecture 7: Introduction to Root-Knot Nematodes

Question 1

RKNs (root-knot nematodes)

1. What kind of parasite are they?
2. What stylet do they use?
3. J2 length
4. Female diameter

Answer 1

1. Sedentary endoparasites
2. Stomatostylet
3. 200 μm – 380 μm
4. 400 μm – 1.3 mm

Question 2

Are root-knot nematodes obligate biotrophs? Do they have a narrow or broad host range?

Answer 2

Yes, they are obligate biotrophs
They have a broad host range

Question 3

Invasion of RKNs: how does it happen?

Answer 3

Enter the root (~24 hr)
Go to the root tip, and make a J-turn (~48 hr)
Go back up to the vascular cambium and create feeding site (3-4 days)
Nutrient acquisition on giant cells INSIDE a gall (7 days-8 weeks)

Question 4

RNK feeding site

Answer 4

5-7 giant cells inside a gall

Question 5

Giant cells

Answer 5

Inside the gall, formed by RKNs which feed on them
Cells that grow large but don’t divide

Question 6

Above-ground symptoms of RNKs

Answer 6

Slow growth
Wilting despite ample soil moisture
Yellowing of leaves (chlorosis) that is often diagnosed as a nutrient deficiency
Patchiness in the field

Question 7

Below-ground symptoms of RKNs

Answer 7

Root stunting
Swelling of root tips
Gall formation

Question 8

Egg masses

Answer 8

Gelatinous matrix where RNK eggs are laid in
Tolerant of environmental changes, can last several years

Question 9

Reproduction of RNKs: sexual or asexual?

Answer 9

Asexual