Biology Reference
In-Depth Information
Nematodes
In the six decades since the first edition of this topic
was prepared, nematodes have become of major
importance in plant pathology. It used to be stated
that plant pests, insects, and diseases, took a toll of
one-tenth of all our crops. Now we believe that
nematodes alone may cause a 10 % crop loss, and
some place the figure as high as 25 %. The mone-
tary loss is not easy to figure. Guesses range from
$500,000 to $8 billion a year in the U. S. Nematodes
may be as damaging in home gardens as on farms.
Nematodes used to be considered primarily
a southern problem, with the root-knot nematode
the major culprit. Now we know that nematodes
can be as serious in Maine or Minnesota as in
Florida or Texas, and that root-knot species are
responsible for only a fraction of total losses.
A 1957 report from Maryland states that sam-
ples were taken from around the roots of crop
plants on 1210 different farms and gardens, and
that every sample included at least one species of
nematode known to be a plant parasite, with root-
knot nematodes making only 3.2 % of the total.
A 1959 report from New Jersey states that, on the
basis of 2500 soil and root samples taken since
1954, a very conservative estimate of annual loss
in the state is $15 million. The root-knot nema-
todes which are reduced by cold winters, were in
third place because of their importance as pests of
greenhouse crops, including African-violets,
roses, and other ornamentals, as well as vegetable
seedlings. Nematodes (eelworms or round-
worms) are threadlike animals in the phylum
Nematoda (or Nemata). The following two
references were used in the nematode taxonomic
descriptions in this section:
Nickle WR (1991) Manual of agricultural
nematology. Dekker, New York. 1035pp
Blaxter ML, DeLey P, Garey JR, Liu LX,
Scheldeman P, Vierstraete A, Vanfleteren JR,
Mackey LY, Dorris M, Frisse LM, Vida JT,
Thomas WK (1998) A molecular evolutionary
framework for the phylum Nematoda. Nature
392(6671):71-75.
Nematodes live in moist soil, water, decaying
organic matter, and tissues of other living organ-
isms. Some cause diseases of man or animals;
others cause plant diseases. The animal parasites
include hookworms, pinworms, and the worms in
pork causing trichinosis, and they range in length
from less than an inch to nearly a yard. Most plant
parasites are practically microscopic in size,
sometimes just barely visible to the naked eye.
They mostly range from 0.5 to 2 mm long, or
from 1/50 to 1/10 inch.
Nematode diseases of plants are not new. The
wheat eelworm was recorded more than two cen-
turies ago (in 1743); root knot has been
a recognized problem since 1855. Our systematic
investigation of plant parasitic nematodes is very
new. Only in the past few years have we made
surveys to find out how widespread nematodes
are and how many cases of “decline” in plants are
due to them. Nematodes injure plants directly by
their feeding, causing cell death or gross modifi-
cations and general stunting, and indirectly by
affording entrance to bacteria and fungi causing
