Question

The $3^{rd}$ and $4^{th}$ stage juveniles of root-knot nematodes are:

• A. Feeding
• B. Non-feeding
• C. Quiescent
• D. Infective

Hint:

Root-knot nematodes induce giant cell formation in roots, creating their feeding sites.

Answer 1

The Correct Option is D

Root
knot nematode life stages:
J1: Hatches from egg
J2: Infective stage (penetrates roots)
J3: Sedentary, begins feeding
J4: Develops into adult The $3^{rd}$ and $4^{th}$ stages are the infective juvenile forms that penetrate plant roots.

Answer 2

Alternate approach - track the juvenile through its stage-wise role:
The egg contains the first-stage juvenile (J1), which is non-motile and moults inside the egg shell.
The second-stage juvenile (J2) hatches, actively moves through soil, and locates and penetrates a host root, beginning the parasitic phase.
Once inside the root, the juvenile continues developing through the third and fourth stages while remaining associated with the feeding site it has established, retaining its parasitic relationship with the host rather than reverting to a resting or quiescent state.
Since none of these later juvenile stages are dormant or free of the host, and the parasitic engagement with the root persists through J3 and J4, the stages described in the question are classified as infective rather than feeding, non-feeding, or quiescent as separately defined in this scheme.