Various types of Nematode - By Habitat

1. Introduction of nematology
Course: B.Sc. Agriculture
Sem II
Subject: Introductory nematology
Unit: 1

2. Introduction: History of phytonematology.
Economic importance. General characteristics
of plant pathogenic nematodes. Nematode
general morphology and biology.
Unit-1

3. Nematology is an important branch of biological science, which
deals with a complex, diverse group of round worms known as Nematodes
that occur worldwide in essentially all environments. Nematodes are also
known as eelworms in Europe, nemas in the United States and round
worms by zoologists.
Many species are important parasites of plants and animals,
whereas others are beneficial to agriculture and the environment.
Nematodes that the plant parasitic forms are called nematodes and
the study is known as Plant Nematology. The name nematode was derived
from Greek words nema (thread) and oides (resembling).
The damage to plants caused by nematodes is often overlooked
because the associated symptoms, including slow growth, stunting and
yellowing, can also be attributed to nutritional and water related disorders.

4. History of Nematology
In light of the high population numbers of nematodes. N.A. Cobb (1915)
who is considered to be the father of American Nematology, provided a dramatic
description of the abundance of nematode.
Needham, T. (1743)- Wheat gall nematode, Anguina tritici. First record of plant
parasitic nematode. Described associated diseases of wheat and other grains.
Berkeley, M. J. (1855)- Discovered root-knot nematode, Meloidogyne spp in
greenhouse cucumber.
Goeldi, E. A. (1887), Neal, J.C. (1889), Atkinson, G.F. (1989), Bessey, E.A.
(1901)- Contribution in Meloidogyne spp. Distribution, host ranges and disease
complexes .
Schacht, H. (1859)- First reported cyst forming nematode in sugar beet in
GermanyIntroductory Nematology Prof. Avinash S. Mahale

5. Schmidt, A. (1871)- Described sugar beet nematode, Central Europe Heterodera
schachtti Carbon disulfide (CS2) – First report of effective chemical control of
nematodes.
Kuhn, J. (1857)- Described stem nematode, Ditylenchus dipsaci – on teasel heads.
Serious problem to alfalfa, garlic, oats, onion, red clover, rye.
Ritzema Bos, J. (1891)- Discovered foliar nematode, Aphelenchoides fragariae on
straw berry. A. ritzemabosi on chrysanthemum A. Besseyi on rice.
Cobb, N. A. (1914 to 1932)- Father of Nematology (America).
Developed techniques for sampling soil for nematodes.
Wet screening for extraction of nemas from soil.
Methods of preserving/sectioning/mounting nematodes.
Filipjev, I. N. (1930)- Russian Scientist published a book “Nematodes that are of
importance to Agriculture”.
Chitwood, B. G.(1937)- Published a book “Introduction to Nematology”

6. New Era in Nematology (1941-1990)
• Cannon, O. S. (1941)- New York – Potato root eelworm (Golden
Nematode) Heterodera rostochiensis (Globodera rostochiensis)
• Carter, C. C. (1943)- Discovery of D.D. (1, 3 Dicloropropane) soil
fumigant for control of golden nematode.
• Christie, J. R. & Albin, F. E. (1944)- Discovery of races of root-knot
nematodes.
• Chitwood, B. G.(1949)- Discovered genus Meloidogyne. Described
several species of root-knot nematodes which made possible to :
• Determine the host range of individual species.
• Design keys for their identification based on morphological
differences.
• Develop crop cultivars resistant to certain species.

7. •Study individual species cytologically and biochemically
•Early (1950)- Declining citrus in Florida due to burrowing nematodes,
Radopholus similis.
•Christie, J. R. and Perry, V. G. (1953)- Demonstrated the importance of
several ectoparasitic species (Belonolaimus, Dolichodorus, Xiphinema,
Trichodorus etc.)
•Moutain, W. B. (1955)- Culturing plant parasitic nematodes under sterile
conditions.
•Hewitt, W. B. (1958) - Discovery of transmission of virus diseases.

8. History of Nematology India
• 1901 : Barber, C. A.- Root-knot nematode infesting tea in
south India – First report of plant parasitic nematode in India.
• 1906 to 1919- Root-knot nematode – Black pepper in Kerala,
Ufra disease of rice (Ditylenchus angustus)
• 1934: Ayyar, P. N. K.- Root-knot nematode infesting
vegetables and other crops
• 1936: Dastur, J. F.- White tip nematode of rice
(Aphelenchoides spp.)
• 1961: Jones, F. G. W.- First authentic report on potato cyst
nematode, Heterodera (Globodera) rostochiensis from
Nilgiris.
• 1965- First authentic report on Radopholus similis on banana
from Kerala.

9. Economic Importance of Plant Parasitic Nematodes
The plant parasitic nematodes play a vital role in crop production as
most of the crop including field, orchards, vegetables, kitchen garden,
ornamental crops are attacked by various species of nematodes. More than
2000 species of phytonematodes belonging to about 200 genera have been
described; while it is estimated that about 42000 species of phytonematodes
may be present.
It has been estimated that on global basis 12 percent crop loss due to
diseases, 7 percent due to insects, 3 percent due to weeds and 11 percent due
to nematodes. The annual crop losses due to these obligate parasites have
been estimated to be about $78 billion worldwide. Estimated overall average
annual yield loss of the world’s major crops due to plant parasitic nematodes
was 12.3%. Estimated losses due to plant parasitic nematodes in developing
countries were 14.6% and 8.8% for developed countries. On worldwide
basis, the ten most important genera were reported to be Meloidogyne,
Pratylenchus, Heterodera, Ditylenchus, Globodera, Tylenchulus,
Xiphinema, Radopholus, Rotylenchulus and Helicotylenchus.

10. In India, the losses caused in different crops are due to the following
major nematode species.
• The seed gall nematode, Anguina tritici is responsible for ear
cockle disease of wheat in Northern India. It also causes tundu or
yellow slime disease with the association of a bacterium,
Clavibacter tritici. The overall damage is one percent but
sometimes it is as high as 80 percent.
• The root-knot nematode, Meloidogyne spp. is one of the few
nematodes known to the farmers due to the spectacular symptoms
of root gall formation on vegetable, pulses, fruits and ornamental
plants. The percent yield losses due to this nematodes has been
estimated to the tune of 28-47 percent in tomato, 26.2-50 percent
in brinjal, 19.7-33 percent in chillies, 6.0-90 percent in okra, 38-
47.2 percent in bitter gourd and 18-33 percent in melons at
different AICRP projects in India.

11. • The cereal cyst nematode, Heterodera avenae causes Molya
disease of wheat and barley in the states of Rajasthan, Haryana,
Punjab, Delhi, U.P., Himachal Pradesh, Jammu & Kashmir. It may
cause up to 50 percent or even a total loss of the crop.
• The reniform nematode, Rotylenchus reniformis attacks a large
number of plants and causes considerable losses to vegetables and
pulses varying from 4.8 to 14.9 percent loss in yield in different
crops.
• Citrus nematode, Tylenchulus semipenetrans causes slow decline
disease of citrus and also associated with ‘die-back’ in citrus.
• The burrowing nematode, Radopholus similis causes severe
damage to many fruit crops including banana, spice crop and other
plantation crops. It is responsible for spreading decline of citrus,
black head disease of banana and root-rot disease of crops.

12. • The golden nematode of potato, Globodera rostochinensis is a
serious problem in Nilgiri and Kodaikanal hills. An average
loss of 9 percent is caused by this nematode.
• The root lesion nematode, Pratylenchus coffeae is important
pest of coffee in South India. It causes foot-rot of young plants
and decline or die-back of older plants.
• The above examples include only the major nematode pests.
Besides infesting alone, they are also known to be associated
with various bacteria, fungi and viruses in causing complex
plant diseases which further increases the losses in yield of
crops. The nematode problem is more important in developing
countries, in tropical and sub-tropical regions.

13. Characteristic of nematode
Nematodes are highly abundant, non-segmented worms that
are present in a variety of habitats. Many are free-living (such as
those that live in the soil), while others are parasitic and must attach
themselves to a plant, insect, animal or human host to survive and
reproduce. Some common nematodes include roundworms, Ascaris,
hookworms and Trichinella. There are a number of characteristics
shared by members of this large phylum.

14. Life cycle
The nematode life cycle is typically divided into six stages: the
egg, four juvenile stages and the adult. The duration of any of these stages
and of the complete life cycle differs for different species, and also
depending on factors such as temperature, moisture and plant host.
Under favorable conditions in the tropics many species have
relatively short life cycles, with several generations possible per season.
This can lead to rapid population build up from just one (if self-fertilizing)
or two nematodes.
Nematodes can survive unfavorable conditions, such as a dry
season or a cold winter.
Different species survive best at different life stages, for example
Heterodera species survive best as eggs encapsulated within cysts,
Ditylenchus species as fourth stage juveniles, and Anguina species as
second stage juveniles

15. Morphology
Nematodes are vermiform in appearance. Their body is cylindrical
more or less tapered at the ends and covered with a cuticule. The mouth IS
at the anterior end. It "has a stylet,-a hardened cuticular structure analogous
to an hypodermic syringe. The stylet is extendable and a nematode feeds by
perforating the cell walls sucking the cell contents. Suction is produced by
the contractions of the m-dian bulb, a muscular bulb which acts like a pum.
The digestive tube includes the oesophagus, the intestine and the
rectum, which opens to the exterior through an anus situated at the base of
the tail.
The male reproductive apparatus consists of one or two testes and two
spicules which are the copulatory organs and which‘ are extruded through
the anus, guided by the gubernaculum. The caudill bursa, when present, is a
membrane that holds the female during mating.

16. The female reproductive structures include one or two ovaries,
a spermatheca, a uterus and a vagina. The position of the vulva
varies with species, but it is generally situated at the middle of
the body when there are two ovaries.
Nematodes also have:
-An excretory system
-A muscular system consisting of four muscle fields
- A nervous system composed of a nerve ring, nerve cords, tactile
sense organs and chemo-receptors.

18. Nematode types
Plant parasitic nematodes can be separated into aerial parasites –
those feeding on above-ground parts of plants – and root and tuber
parasites – those feeding on below-ground parts. They can also be
grouped by their feeding behavior and motility into three main groups:
• Migratory endoparasites– mobile nematodes that feed inside the plant
root tissue.
• Sedentary endoparasites – nematodes that, once they have reached a
feeding site inside the plant, cease to be mobile and feed from a fixed
location.
• Ectoparasites – nematodes that feed on the plant from the plant

19. Migratory endoparasites
All life stages of migratory endoparasitic nematodes are mobile
except the egg. The nematodes burrow through the plant from cell to
cell, or may leave the plant tissue in search of new feeding sites. Whilst
feeding they commonly lay eggs both inside the plant cortical tissue
and also in soil surrounding the root tissue. Damaged cells release
toxins which kill neighboring cells, resulting in small spots or lesions
of necrotic tissue.
Root rot fungi and bacteria are often associated with
infestations of migratory endoparasitic nematodes, which enter the
plant tissues through areas damaged by nematodes.

20. Sedentary endoparasites
Sedentary endoparasitic nematodes invade plant tissue usually
as newly hatched second-stage juveniles – the ‘infective’ wormlike
stage. They move through the soil to locate host roots, and then through
the plant tissue to find a feeding site. At the feeding site the female
develops, remaining permanently sited for the duration of her life. As
she develops, her body swells to a spherical, lemon, kidney, or ovoid
form. The nematode feeds on a relatively small number of cells, which
are regulated by the nematode with growth substances. Some groups
(e.g. cyst and root-knot nematodes) cause ‘giant’ feeding cells to form
in the host plant.

21. The males remain worm like, feeding on the surface of the root
for a few days, during which they may or may not fertilize the females
before moving into the soil where they die.
Female sedentary endoparasitic nematodes generally produce a
large number of eggs, which remain in their bodies (e.g. cyst nematodes –
Heterodera spp.) or accumulate in egg masses (e.g. root-knot nematodes –
Meloidogyne spp.) attached to their bodies. Some other nematodes are
sedentary, but only semi-endoparasitic, such as the reniform
(Rotylenchulus spp.) and citrus (Tylenchulus semipenetrans) nematodes,
which become only partly embedded in the root tissue.

22. Ectoparasites
Ectoparasitic nematodes feed externally, on the surface of the
plant, usually on root hairs or cortical tissue. They are often found in high
densities, but do not always pose a problem. However, they may cause
serious damage if the plant is suffering from other biotic or abiotic
stresses (e.g. fungal attack or low water availability). Examples of
ectoparasitic nematodes are ring nematodes (Criconemoides spp.), spiral
nematodes (Helicotylenchus spp.) and the aerial rice white-tip nematode
(Aphelenchoides besseyi).
It is well recognized that some ectoparasites transmit plant
viruses, for example some species of dagger nematodes (Xiphinema
spp.), needle nematodes (Longidorus spp.) and stunt nematodes
(Trichodorus and Paratrichodorus spp.).

23. Figure Reference:
1.http://www.aapsnet.org/edcenter/intropp/PathogenGroups/Page
s/IntroNematodes.aspx
Web References:
1. http://horizon.documentation.ird.fr/exl-
doc/pleins_textes/divers11-06/17336.pdf
2. http://www.livestrong.com/article/62037-characteristics-
nematodes/