FUNDAMENTALS OF PLANT
PATHOLOGY
Course No.- PP-121
Semester: 2nd
UNIT-6: NEMATODES
Dr. Paritosh Kumar
Dr. M. Ranjana Devi
Assistant Professor-cum-Junior Scientist
Department of Plant Pathology
Tilka Manjhi Agriculture College, Godda
BAU, Ranchi
Contents
NEMATODES
• General morphology
• Reproduction
• Classification
• Symptoms and nature of damage caused by plant nematodes
(Heterodera, Meloidogyne, Anguina etc.)
The word “NEMATODE” is derived from two Greek words- ‘Nema’ meaning thread and ‘Oides’ meaning
resembling or form.
✓ They are thread like forms therefore they are also called threadworms. They are also known as roundworms
being tubular in shape and rounded in cross section.
✓ Britishers called them eelworms because of their general shape and serpentine movement resemble that of
eels.
HABITAT: Nematodes dwell in all types of habitats on earth from ocean depths to top of the mountains, from barren
lands to cultivated fields and from meadows to tropical forests.
❑ Most of the several thousand species of nematodes live freely in fresh water or salt water or in the soil and feed on
microorganisms and microscopic plants and animals.
✓ Numerous species of nematodes attack and parasitize humans and animals in which they cause various
diseases. Example:
Ascaris lumbricoides Enterobius vermicularis
(intestinal roundworm) Wucheraria bancrofti (pinworm- in faeces of
(filarial worm causing children)
elephantiasis)
✓ Members of the Phylum Nematoda (round worms) have been in existence for an estimated one billion years,
making them one of the most ancient and diverse types of animals on earth.
✓ Several hundred species are known to be parasitic, feed on living plants obtaining food with spears or
stylets causing a variety of plant diseases worldwide.
✓ The vast majority of nematodes are also beneficial microbial feeders and reside in the soil. They help promote
healthy soil environments, that includes nutrient recycling.
NEMATOLOGY: Scientific discipline concerned with the study of nematodes.
✓ Plant Nematology (Agricultural Nematology/ Phyto- Nematology): Deals exclusively with those forms of nematodes
which parasitize plants and are of economically important to agriculture, horticulture and forestry.
✓ Father of American Nematology: N. A. Cobb
✓ First plant parasitic nematode discovered is Anguina tritici by Needham (1743)
✓ The study on these animal and human parasites are known as Helminthology.
✓ Annual worldwide losses caused by nematodes on life sustaining crops (banana, coconut, all grains & legumes, potato,
sugarcane are estimated to be about 11%. And losses for other economically important crops (vegetables, fruits & non
edible field crops) are about 14%.
✓ According to Sasser (1989), 20.6% of global loss of crop yield is due to nematodes. Out of all, Meloidogyne is most
damaging followed by Pratylenchus and Heterodera.
✓ Eg: Anguina tritici –Seed gall nematode of wheat, Meloidogyne sp.- root knot nematode, Heterodera avenae- cyst
nematode of wheat, oats and barley.
GENERAL MORPHOLOGY
SHAPE AND SIZE
a) Body length: Plant parasitic nematodes are small, 300-1000µm with some up to 4mm long, by 15-
35µm wide. The length may vary from 0.2 mm (Paratylenchus) to about 11.0mm (Paralongidorus
maximus). Their body width vary from 0.01 to 0.05 mm.
• Longest plant parasitic nematode: Paralongidorus epimikis
(reaching up to 1.2cm in length. Their small diameter makes them invisible to the naked eye but
they can be observed easily under the microscope.)
• Placentonema gigantissima largest size /giant nematode (8.4 metres and a diameter of
2.5 cm)
❖ Body of nematode cannot be easily divided into head, thorax and abdomen. Often the anterior most
extremity of the body bearing mouth and lips is called Head. The portion beyond the anus is known as Tail.
b)Shape: They are typically vermiform, thread like, eel like/ tubular in shape, tapering from both ends
and round in cross section with smooth, unsegmented body without legs and appendages. Male and female
generally look alike. However in some nematode species, their females (Heterodera, Meloidogyne) become
swollen upon maturity while males remain vermiform in all genera of parasitic nematodes.
• Nematodes are triploblastic, bilaterally
symmetrical, unsegmented, vermiform and
colourless animals. The plant parasitic nematodes
are slender elongate, spindle shaped or fusiform,
tapering towards both ends and circular in cross
section.
• In few genera, the females on maturity assume
pear shape (Meloidogyne), globular shape Globodera
(Globodera), reniform (Rotylenchulus reniformis)
or saccate (Tylenchulus semipenetrans).
Tylenchulus semipenetrans
Genera of the most common plant parasitic nematodes
1. Cyst nematode Globodera sp. & 9. Ring nematode Criconemella sp.
Heterodera spp. 10. Root – knot nematode Meloidogyne sp.
2. Dagger nematode Xiphinema sp. 11. Sheath nematode Hemicycliophora sp.
3. Foliar nematode Aphelechoides sp. 12. Spiral nematode Helicotylenchus sp.
4. Lance nematode Hoplolaimus sp. 13. Sting nematode Belonolaimus
5. Lesion nematode Pratylenchus sp. 14. Stubby-root nematode Paratrichodorus spp & Trichodorus spp.
6. Needle nematode Longidorus sp. 15. Stunt nematode Tylenchorhynchus spp
7. Pin nematode Paratylenchus sp. 16. Golden nematode- Globodera rostochiensis
8. Reniform nematode Rotylenchulus sp.
ECOLOGIAL CLASSIFICATION OF PLANT PARASITIC NEMATODE
There are two major classes: I. Above ground feeder II. Below ground feeder
I. Above ground feeders
II. Below ground feeders
Based on their feeding habits
The nematodes can be divide into 3 types:
1. Ectoparasitic nematodes
2. Semi endo-parasitic nematodes
3. Endo-parasitic nematodes.
1. Ectoparasitic nematodes:
• They do not normally enter the root tissue but feed from the outside crop plant.
• These nematode live freely in the soil and move closely or on the root surface,
feed intermittently on the epidermis and root hairs near the root tip.
• Eg. Ring nematode (Mesocriconema xenoplax)
1. Ectoparasitic nematodes:
A. Migratory ectoparasite : These nematodes spend their entire life cycle free in the soil . When
the roots are disturbed they detach themselves. (e.g.) Criconemoides spp., Paratylenchus spp., and
Trichodorus sp., etc.,
B. Sedentary ectoparasites : In this type of parasitism the attachment of nematode to the root
system is permanent or they become sedentary for their entire life. (eg.) Hemicycliphora arenaria, and
Cacopaurus pestis etc.,
2. Semi endo-parasitic nematodes :
The anterior part of the nematode, head and neck being permanently fixed in the cortex and the
posterior part extents free into the soil.
(e.g.) Rotylenchulus renifomis and Tylenchulus semipenetrans.
3. Endo-parasitic nematodes:
The entire nematode is found inside the root and the major portion of nematode body found inside the plant
tissue.
a. Migratory endo-parasite: These nematodes enter host plant, move in the cortial parenchyma of
host root and feed from within. While migrating they feed on cells, multiply and cause necrotic lesions.
(eg.) Hirschmanniella spp., Pratylenchus spp and Radopholus similes etc.
Lesion nematode (Pratylenchus spp )
b. Sedentary endoparasite : The second stage larvae penetrate the rootlets and become sedentary
through out the life cycle, inside the root cortex. (eg.) Heterodera spp and Meloidogyne spp.
CLASSIFICATION Phylum NEMATODA Class Adenophorea
Class Secernentea Order Tylenchida Order Dorylaimida
Genus 1. Paratrichodorus
Genus 1. Anguina
2. Trichodorus
2. Globodera
3. Heterodera
4. Meloidogyne
Phylum NEMATODA
Free living Parasitic nematodes
eg. Caenorhabditis elegans
b) Parasitic to invertebrates c) Parasitic to plants (PPN)
a) Parasitic to human (Helminthes)
(insects) Plant Parasitic Nematodes
eg. Ascaris lumbricoides
Entomo Pathogenic Nematode (EPN) eg. Anguina tritici
eg. Heterorhabditis
REPRODUCTIVE SYSTEM
• Nematodes are dioecious, both sexes look similar. Reproductive system is
tubular. Generally reproduction is sexual (usually males are smaller than
females and have a characteristically bent or fan-shaped tail) or
Parthenogenetic reproduction (reproduce asexually by parthenogenesis).
Some nematodes are hermaphrodite, and keep their self-fertilized eggs
inside the uterus until they hatch.
• Sexual reproduction is also known as amphimetic reproduction.
Parthenogenetic reproduction is also common phenomenon in Meloidogyne
and Tylenchus semipenetrans
• During copulation, one or more chitinized spicules move out of the cloaca
and are inserted into the genital pore of the female. Amoeboid sperm crawl
along the spicule into the female worm.
• Some nematodes are hermaphrodite, and keep their self-fertilized eggs
inside the uterus until they hatch.
MALE NEMATODES
Males are usually smaller than their female counterparts. Basic male reproductive
structures include:
1. one testis 2. a seminal vesicle 3. a vas deferens opening into a cloaca.
One testis is most common, but two testis are found in some species, while in others one testis
is reduced. Spermatogonia are produced in the testis and stored in the seminal vesicle until the
nematode mates.
❖ Sperms are formed in testis, stored temporarily in seminal vesicle.
❖ Spicules are protusible and help in insemination of females during mating. Movement of
spicules is guided by plate like structure called Gubernaculum (cuticularised structure
lying beneath the pair of spicules).
❖ At the tail end, two filamentous cuticular expansions are found and are commonly called
as Bursa helps in clasping the female during mating.
❖ Spicules, gubernaculum and bursa are secondary sex organs.
FEMALE NEMATODES
Basic female structures include: • The ovary produces oogonia, which later develop into oocytes.
1. one or two ovaries (gonad) • The females have two ovaries which are connected by oviducts
2. Oviduct to two different uteri (uteri is plural for uterus), a vulva and
3. Uterus vagina, as well as a seminal receptacle that stores sperm from a
4. Spermatheca male.
5. Vagina
• All nematodes lay eggs. Syngamy, or cross fertilization, is
6. A vuvla (gonoduct).
common in most nematodes. Hermaphroditism also occurs,
with the nematode gonads producing spermatozoa first and
storing them until the eggs are produced. Parthenogenesis is
also a normal means of reproduction in some nematodes.
SYMPTOMS AND NATURE OF DAMAGE CAUSED BY PLANT
NEMATODES
ABOVE GROUND SYMPTOMS
1. Dwarf/ Retarded growth in patches
2. Increased growth( in few specific cases)
3. Discoloration of foliage
4. Distortion and abnormal growth
a. Crinkled or distorted foliage
b. Seed galls
c. Leaf galls
5. Temporary wilting
➢ Pratylenchus penetrans in cherry
➢ Heterodera avenae in wheat and barley
➢ Globodera rostochiensis (Golden nematode) in potatoes
➢ Meloidogyne incognita in many vegetables and ornamental
hosts
➢ Ditylenchus dipsaci produces multiple
crowns in sugar beet and increased
tillering in oats (not recorded from India
so far).
➢ Meloidogyne exigua and Pratylenchus coffeae cause
leaf chlorosis in coffee.
➢ Foliage distortion in chrysanthemum is caused by
Aphelenchoides ritzemabosi.
➢ Seed galls by Anguina tritici in wheat.
➢ Anguina graminis and Ditylenchus graminophilus produce
leaf galls in many grasses.
BELOW GROUND SYMPTOMS
1. Reduced root system and injured root tips
2. Root lesions
Reduced root
3. Root rots system Root lesions
4. Root proliferation (root sprangling)
5. Root knot or root galls
6. Cyst on roots
ASSOCIATION OF NEMATODES (AS VECTORS) WITH
OTHER PLANT PATHOGENS
A. Nematode- bacterium Association
B. Nematode- fungus Association
C. Nematode- virus Association
A. Nematode- bacterium Association
1. Tundu disease/ Yellow slime/ ear rot of wheat:
• Nematode- Anguina tritici which acts as a vector carrying the bacterium Corynebacterium tritici
causing Tundu disease.
2. Vascular wilt in potato and tomato:
• Nematode- Meloidogyne incognita and bacterium Pseudomonas solanacearum
B. Nematode- fungus Association
1. Damping off of Cotton: Nematode- Meloidogyne incognita and fungal pathogens involved are Pythium
sp., Rhizoctonia solani
2. Vascular wilt: Nematode- Meloidogyne incognita and fungal pathogens involved are Fusarium sp.,
Verticillium sp., Phytophthora sp., Rhizoctonia sp., Sclerotium sp.
C. Nematode- virus Association
1. NEPO viruses:
• Eg: Grapevine fan leaf virus with Xiphinema
• Xiphinema spp., Longidorus spp., and Paralongodorus spp. tansmit the ring spot viruses which are called
“NEPO” derived from Nematode transmitted polyhedral shaped particles.
2. NETU viruses:
• Eg: Tobacco rattle virus with Paratrichodorus spp. and Pea early browning virus with Trichodorus spp.
• Paratrichodorus spp and Paratrichodorus spp. transmit the rattle viruses and are called “NETU”
derived from Nematode transmitted tubular shaped particles.
