Nemetodes

Nematodes

    • Nematodes are tiny creatures which live in soil or in the tissues of living plants and animals.
    • The juveniles (larvae) are tube-shaped and look like tiny worms.
    • Adults may be round or lemon-shaped.
    • Adult females of some species, including the citrus nematode, are sedentary.
    • They live all the time within a group of plant cells which have been modified into a feeding and breeding site.
    • Most nematodes are so small (less than 2 mm) that they cannot be seen even in a large group except with a powerful microscope.
    • A handful of ordinary soil may contain thousands of nematodes since these are mostly invisible, they are usually treated as a plant disease rather than a plant pest.
    • Most of the nematodes which infest plants, live in soil and attack the roots.
    • They pierce the walls of the root cells with a hollow tube like (stylet) and withdraw the contents of the cell.
    • Nematodes can move into the cell or move between cells.

    Slow Decline
    • Caused by the citrus nematode Tylenchulus semipenetrans
    Distribution
    • The citrus nematode is a world-wide pest of citrus plant.
    Symptom
    • A tree infected with citrus nematodes may survive for many years after it has been infected.
    • Main effect of nematode infestation is the "slow decline".
    • Symptoms include the dieback of small branches, yellowing of leaves and fruits are smaller in size.
    • Reduced number of feeder roots.
    • Citrus nematodes are too small to be seen, but the attached roots have a gritty appearance because of the egg masses which cling to them.
    • Authentic diagnosis must be made in a laboratory with a good microscope.
    • Growers may expect some citrus nematodes to be present in most of the orchard soils.
    • Nematodes do not become a problem unless populations are very high (i.e. more than 10,000 larvae per 500g of soil).
    • Growers planting new orchards must be very careful not to introduce nematodes accidentally, in the soil around roots of seedlings.
    • If nematodes are already present in the soil in large numbers the best protection is to use resistant rootstocks such as trifoliate orange or Troyer citrange.

    Life Cycle

    • The typical life cycle of the nematode is: Egg, four larval satges viz., L1, L2, L3, L4 and adult female

Last modified: Friday, 22 June 2012, 6:15 AM