B.Sc. Agri II IN U-2 Classification of Nematodes

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 Germany Introductory 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.

17. 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

18. 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.

19. 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.

20. 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.

21. 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.).

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