Nodule formation involves a sequence of multiple interactions between Rhizobium and roots of the host plant. The principal stages in the nodule formation are given below.

(I) Amature nodule establishes a direct vascular connection with the host for exchange of nutrients.

(II) Root hair curls and the bacteria invade the root hair.

(III) Rhizobia multiply and colonise the surrounding of roots and get attached to epidermal and root hair cells.

(IV) The infection thread is produced carring the bacteria and grows into the cortex of the root.

(V) The bacteria get modified into rod-shaped bacteroids and cause inner cortical layer and pericycle to divide to

form nodule.

The correct sequence is