Nematodes, especially plant-parasitic ones, do a great deal of harm to plants,
mostly by attacking the root systems. These tiny roundworms persist in the topmost
layer of soil and eat the belowground portion, which prevents the plant from getting the
vital nutrients and water it needs. As a result, afflicted plants show signs such as
stunted development, which is noticeable even under ideal circumstances, and
withering even in the presence of adequate soil moisture. The damage also affects the
leaves, which frequently become yellow as a result of nutritional shortages brought on
by compromised root function. Reduced yields are frequently the result of damaged
root systems that are unable to sustain strong plant development. Additionally, the
induction of lesions, galls, and deformities on roots caused by nematode feeding
exacerbates the suffering experienced by plants and creates openings for other
infections. In severe cases-especially in young or weak specimens - the cumulative
effects result in plant death. These consequences highlight the serious threat that
nematodes represent to agricultural output, which calls for the application of a number
of management techniques to lessen their negative effects and protect crop yields and
health. In order to combat nematode infestations, plants have developed a variety of
defense systems that include both chemical and physical tactics. To combat nematode
infection, plants have developed several defense mechanisms which include both
physical and chemical nature. Physical barriers that prevent nematodes from
penetrating roots and causing harm include thicker cell walls, lignification, and the
creation of suberin layers. In reaction to nematode infestation, plants simultaneously
release an abundance of secondary metabolites. These substances, which have
nematicidal qualities and directly target nematodes or prevent them from establishing feeding sites, include phytoalexins, phenolics, and terpenoids. Keeping the above
mentioned facts in mind, this chapter tends to focus primarily on the damages caused
by the plants to their hosts and the nature of defense strategies adopted by them.
Keywords: Allelochemicals, Chlorosis, Defense, Host, Nematodes, Oxidative damage.
