Introduction

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 forms an important group of obligate parasites of
plants and animals, whereas others are beneficial to agriculture and the environment. Nematodes
that are parasites of man and animals are called helminthes and the study is known as
Helminthology. 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).
Nematodes are numerically 2nd most abundant organism after insects. Out of estimated
species, i.e., 5,00,000, only 25,000 are known till today, out of which more than 1,800 species
are found to be associated with plat diseases. The nematodes rarely kill a plant to ensure their
survival. However, they may play the role of incitant, aggravator, vector or predisposer of plants
to secondary attack by other plant pathogens. Annual crop losses due to these obligate parasites
have been estimated to be about $ 78 billion word-wide and $ 8 billion for U.S. growers. The
estimated annual crop loss in Tamil Nadu is around Rs. 200 crores.
Estimated loss of some important crops:
Serial no. Crop Loss (%)
1. Banana 19.7
2. Coconut 17.1
3. Brinjal 16.9
4. Sugarcane 15.3
5. Cowpea 15.1
6. Coffee 15.0
7. Citrus 14.2
8. Potato 12.2
9. Cotton 10.7

For ease of study and host specify the nematodes may be studied under the heading of:
1. Free living nematodes
 This is a group of nematodes focused less, as not considered economically important.
They may be marine (Chaetostoma, Chromadora, Deontostoma. etc.) or fresh water
nematodes (Plectus, Dorylaimus, Mononchus, Rhabditis etc.). There are some free living
soil inhibiting nematode genera.
Some important genera of free living nematodes:
 Caenorhabditis elegans and C. briggsae: free living, soil inhibiting, bacterial feeding.
 Caenorhabditis elegans: used as model organism (proposed by Sydney Brenner in 1965)
to study development, neurobiology, and aging, due to its small life cycle (3 days), small
size (1.5 mm adult), small genome (97 million base pairs spread among six
chromosomes), and anatomical simplicity (>1000 cells), including the 302-cell
hermaphrodite nervous system. In addition it is the only organism to have
its connectome (neuronal "wiring diagram") completed.
 Brenner, Sulstin and Horvitz received Nobel prize in Physiology or Medicine in 2002, for
their work on cell linage pattern and role of genes in regulating and apoptosis in
Caenorhabditis elegans.
 Caenorhabditis Genetic Center: at National Institute of Aging, University of Missouri,
USA. This institute is responsible for maintenance, genetic map, genetic nomenclature,
storage, and distribution of mutants.
 Panagrellus redivivus: biological indicator of pollution in both terrestrial and aquatic
ecosystems.
2. Parasites of vertebrates
a) Parasites of humans
i) Ascaris lumbricoides: intestinal roundworm, infecting approx. 25% of world
population. It causes anemia, and heavy infection may lead to intestinal
blockage.
ii) Enterobius vermicularis: parasite of caecum (1cm long). Cause severe itching
in anal area, due to egg lying by the female in perianal area.
iii) Wucheraria bancrofti: filarial worm, parasite of lymphatic system, causing
inflammation of limbs and genital organs the disease is known as elephantiasis.
In India more prevalent in coastal areas of South India, West Bengal, Bihar,
and Odisha. The nematode is transmitted by mosquitoes.
b) Parasites of vertebrates other than human
 i) Trichuris spp.: Whipworm (30-50 cm long). Parasite in colon, rectum, and
appendix of dogs and pigs, etc.
ii) Dioctophyma renale: Giant kidney worm (up to 90 cm long), parasite of dog.
iii) Haemonchus contortus: blood sucking nematode of sheep, goat, and cattle
stomach, may cause anaemia.
iv) Ascaridia galli: most common ascarid worm parasite in small intestine of
chicken.
3. Parasites of invertebrates
i) Mermis nigrescens: parasites of grasshopper
ii) Romanomermis culicivorax: parasites of mosquitoes (Aedes, Anopheles,
Culex, etc.). Used as biological control of mosquitoes.
iii) Steinernema and Heterorhabditis: used as biological control of a large incest
group. These nematodes carry and release bacteria (Xenorhabdus and
Photorhabdus spp.) inside insect haemocoel which leads to septicemia and
kills the insect host, in return it provide nutrition to insect cadaver.
4. Parasites of plants
The phyto-parasite nematodes are mainly root parasites while few are parasite to
aerial plant parts. The most common genera of plant parasitic nematodes
are Aphelenchoides (foliar nematodes), Ditylenchus, Globodera (potato cyst
nematodes), Heterodera (cyst nematodes), Meloidogyne (root-knot nematodes),
Pratylenchus (lesion nematodes), and Xiphinema (dagger nematodes).
Several phytoparasitic nematode species also act as a vector of viruses. Few
examples are: Xiphinema index, vector of grapevine fan leaf virus, Xiphinema
diversicaudatum, vector of arabis mosaic virus.
The soils in a hectare of all agro ecosystems typically contain billions of plant parasitic as
well as beneficial nematodes. 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.

History of Plant Nematology

The very early mention of nematodes was done in Vedas (6000-4000 BC), under the
name Sanskrit name of Krmin or Krmi. Vedas divided them into two broad group, i.e., Drstam
(visible) and Adrstam (invisible). Further, mention of nematodes was done in Ayurveda (3000
BC and later). References of Ascaris can also be traced in Chinese literature named “Huang Ti
Nei Ching” or “The Emperor’s Classic of Internal Medicine” (2700 BC). 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 nematodes. He
stated, “If all the matter in the universe except the nematodes were swept away, our world still
would be dimly recognizable we would find is mountaintops, valleys, rivers, lakes and oceans
represented by a film of nematodes. The statement “ sowed cockle, reaped no corn” in
Shakespeare’2 “Love’s Labour’s List”’ act4, scene 3, as suggested by Throne (1961) possibly
the first record of plant parasitic nematodes in 1549. The nematode that Throne suspected to be
in that reference actually was described by Needham in 1743. Subsequently, discovery of
microscope and developments in various disciplines of science led to the discovery of plant
parasitic nematodes and the disease caused by them. Some of the important milestones on the
history of plant nematology are listed below in chronological order.
1656 – Borellus – discovered the first free living nematode ‘vinegar eels’ (Turbatrix aceti).

1743 – Needham – Discovery of wheat seed gall nematode Anguina tritici, the first plant
parasitic nematode to come to the attention of the early investigators.
1855 - Berkeley – observed root-knot nematode (Meloidogyne spp.) from root galls of cucumber
plants in greenhouse in England.
1857 - Kuhn – Reported the stem and bulb nematode, Ditylenchus dipsaci infesting the heads of
teasel.
1859 - Schacht – described the reason behind sugarbeet decline in Europe as cyst nematode.
1871 – Schmidt – named Sugarbeet cyst nematode was as Heterodera schachtii.
1873 - Butschli – Descriptions of the morphology of free –living nematodes.
1879 – Cornu – first specific mention of root knot nematode as a causal agent of root knot of
Onobrychis sativa, caused by Anguillula marioni (Meloidogyne sp.).
1884 - deMan – Taxonomic monograph of soil and fresh water nematodes of the Netherlands.
1889 – Atkinson and Neal – Publication about the root-knot nematodes in the United States.
1891 – Ritzema-bos – discovered the foliar nematode Aphelenchoides fragariae on strawberry.
1892 – Liebscher – reported pea cyst nematode Heterodera goettingiana on pea.
1892- Atkinson-Report of root-knot nematode and Fusarium complex in vascular wilt of cotton.
1907- N.A.Cobb – joined the USDA and considered to be the Father of American
Nematology
1913 – N.A.Cobb – published a book ’Contributions to the Science of Nematology”.
1914 – N.A.Cobb – coined the term “nematology”. Contributions to the Science of Nematology.
1918 – N.A. Cobb – Development of methods and apparatus used in Nematology.
1933 – T. Goodey – Book on “Plant parasitic nematodes and the diseases they cause”
1934 – Filipjev – Book on “Nematodes that are importance for Agriculture” translated from
Russian to English in 1941 by S.Stekhovan uner the title “A Manual of Agricultural
Helminthology”.
1943 – Carter-Description of nematicidal value of D-D which is used in the era of soil
fumigation.
1945 – Christie – Description of the nematicidal value of EDB.
1948 – Allen – Taught the World’s first formal university course in Nematology at the
University of California, Berkeley.
1950 – Oostenbrink – Wrote a Book of on “The Potato Nematode, A dangerous parasite to
Potato Monoculture”.
1951 – Christie and Perry – Role of ectoparasites nematodes as plant pathogens. T.Goodey –
Wrote a book on “Soil and fresh water nematodes”. Food and Agriculture Organisation of
the United Nations organized the first International Nematology course and
Symposiumheld at Rothamstead Experiment Station, England.
1953 – discovery of Borrowing nematode (Radopholus similis) causal organism behind
spreading decline of citrus in Florida (USA).
1955 – discovery of root lesion nematode “Pratylenchus penetrans” causing peach replant
problem in Canada. Frist ever attempt to study etiology of a nematode alone was made by
Mountain and Patrick on the same nematode, they also proved ‘Koch’s postulate’ in order to
prove pathogenicity of this nematode for the first time. In the same year, European Society of
Nematologists founded.
1956 – Nematologica – The first journal published entirely for Nematology papers from The
Netherlands.
1958 – Hewitt, Raski and goheen – first report of virus transmission by nematodes (Xiphinema
index transmitting fan leaf grapevine virus, in grapevine), in USA.
1961 – Society of Nematologists founded in the United States.
1967 – Organization of Tropical American Nematologists founded.
1969 – Journal of Nematology was first published by the Society of Nematologists, USA.
1973 – Nematologa Mediterranea – published from Italy.
1978 – Revue de Nematologie published from France
1930s – 1990s – Barron, Duddington, Mankau, Linford, Sayre and Zuckerman – they provided
an insite on the Biological control of plant – parasitic nematodes. Enhanced
understanding of antagonists and related biology enhancing the potential for practical
biocontrol.
1940-s – 1990s – Triantaphyllou – Provided advancement in Cytogenetics, modes of
reproduction/sexually – and information data base for genetics/molecular research.
Enhanced understanding of evolution and taxa interrelationships.
1950s – 1990s – Caveness, Jones, Oostenbrink, Sasser and Seinhorst – International programme
such as International Meloidogyne project – They expanded educational base of
nematologists world wide and provided ecological – taxonomic data base.
1960s- 1990s – Nickle, Poinar and Steiner – Biological control of insects with nematodes.
1960s- 1990s – Brenner, Dougherty and Nicholas – Caenorhabditis elegans developmental
biology and genetics – model system – provided fundamental information on cell lineage,
behavior, gene function ageing and overall genome for this model biological system.
In addition to the above, now the research advancement are in progress in the following areas in
USA from the year 1990. Molecular markers for resistance gene provide efficiency of breeding
for resistance. Cloning of resistance genes - Elucidation of the molecular fundamental
knowledge based on mechanisms of pathogenesis. Cloning of resistance genes- Elucidation of
the molecular. mechanism of resistance. Transgenic host resistance to plant parasitic nematodes
– Great potential, but limitied model system to date.