What are Plant-parasitic nematodes?

Nematodes are usually microscopic, thread-like, colorless and non-segmented roundworms without any appendages. There are harmful (e.g., plant- and animal-parasitic) and beneficial (e.g., entomopathogenic) nematodes. Plant-parasitic nematodes generally cause damage to crops and many other types of plants. Although majority of plant-parasitic nematodes are root feeders, they have different types of association with plants. For example, the root-knot (Meloidogyne sp) and cyst (Heterodera sp.) nematodes have endoparasitic association meaning they live and feed within the tissue of roots, tubers, buds, seeds. Nematodes including stuby-root (Trichodorus sp.), dagger (Xiphinema sp), needle (Longidorus sp), ring (Criconemella sp), stunt (Tylenchorhynchus sp), pin (Paratylenchus sp), and spiral (Helicotylenchus sp) have ectoparasitic association meaning they feed externally on roots through their walls. Some of the nematodes like the reniform (Rotylenchulus reniformis) have semi-endoparasitic association meaning these nematodes feed on the roots by penetrating their anterior (head) region into root tissue and leaving their posterior (tail) region remains outside of the root.