TEXTBOOK OF INTRODUCTORY PLANT NEMATOLOGY (Revised 2nd edition)
RAMAN K. WALIA HARISH K. BAJAJ
Department of Nematology CCS Haryana Agricultural University Hisar (Haryana) 125 004
ICAR
Directorate of Knowledge Management in Agriculture Indian Council of Agricultural Research Krishi Anusandhan Bhavan I, Pusa, New Delhi 110 012
FIRST PRINTED REPRINTED REVISED
Project Director (DKMA)
Incharge (English Editorial Unit) Editing
Chief Production Officer Assistant Chief Technical Officer
MAY 2003 FEBRUARY 2012 JULY 2014
Dr Rameshwar Singh Dr Aruna T. Kumar Dr Sudhir Pradhan Dr Virender Kumar Bharti Ashok Shastri
All rights reserved Š2014, Indian Council of Agricultural Research, New Delhi
ISBN : 978-81-910388-4-2
Price :
600/-
Published by Dr Rameshwar Singh, Project Director, Director of Knowledge Management in Agriculture, Indian Council of Agricultural Research, Pusa, New Delhi 110012, lasertypeset at M/s Print-O-World, 2579, Mandir Lane, Shadipur, New Delhi 110 008, and printed at M/s Chandu Press, D-97, Shakarpur, Delhi 110 092.
Contents Foreword to First Edition Foreword to Second Edition Preface to First Edition Preface to Second Edition
iii v vii ix
PART I: GENERAL NEMATOLOGY 1. 2. 3. 4. 5. 6. 7. B. 9. 10.
Introduction History Morphology Taxonomy Biology Ecology Nature of Damage Pathological Interactions of Nematodes with other Organisms Principles and Practices of Nematode Management General Nematological Techniques
3 12 18 34 58 68 75 82 89 102
PART II: ECONOMIC NEMATOLOGY 11. 12. 13. 14 15 16 17 18 19 20 21
Root-knot Nematodes
Cyst Nematodes Lesion Nematodes Rice Root Nematodes Burrowing Nematodes Citrus Nematodes Reniform Nematodes Lance, Spiral and Stunt Nematodes Ring, Sheath, Pin and Sessile Nematodes Dagger, Needle and Stubby-root Nematodes
Wheat Seedgall Nematodes 22 Aphelenchid Nematodes 23 Genus Ditylenchus 24 Entomopathogenic Nematodes
113 125 136 142 147 153 158 163 169 174 181 186 193 198
xii
Contents
PART III: APPENDIX I. Nematological Glossary II. Classification of Important Phytonematodes III. Common and Scientific Names of Important Phytonematodes IV. Nematodes and Diseases Caused by them V. Nematological Societies and Journals VI. Nematological Centres in India VII. Suggested Further Readings Index
213 220 224 226 229 230 232 236
PARTI
GENERAL NEMATOLOGY
1 Introduction
......
“If all the matter in this universe except the nematodes were swept away, we would find its mountains, our world would still be dimly recognizable hills, valleys, rivers, lakes and oceans represented by a film of nematodes” N.A. Cobb
—
T
HE WORD ‘NEMATODE’ is derived from two Greek words - ‘nema’ meaning thread, and ‘oides’ meaning resembling or form. Thus nematodes 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 also call them eelworms since their general shape and serpentine movement resemble that of eels (marine fishes). In USA, they are often nick¬ named nemas.
NEMATODE HABITATS AND DIVERSITY Nematodes dwell in all types of habitats on earth - from ocean depths to tops of mountains, from hot water springs to icy arctic and antarctic, from barren lands to cultivated fields, and from meadows to tropical forests. Nematodes thus occupy any conceivable habitat on this earth. Nematodes are numerically most abundant among all the metazoans on this earth, and perhaps next only to insects, as far as diversity of forms (species) is concerned. Out of an estimated 5,00,000 species of nematodes, only about 25,000 are known till date. Broadly, nematodes can be grouped into two categories. Most of the nematodes are free-living and their food consists of microorganisms. The dietary requirements of some of these nematodes are still a matter of conjecture. Free-living nematodes in soil form an important constituent of the group of organisms involved in organic matter recycling. Nematodes are also highly successful parasites of plants and animals. Hundreds of parasitic nematodes can be extracted from soil supporting vegetative life anywhere. There is hardly any animal (vertebrate or higher invertebrate) on this earth, which is free from one or the other kind of nematode infection. The parasitic forms have been studied in greater detail since they directly affect the human beings, their domesticated animals and crops. A few examples of each category are cited below.
Free-living nematodes Relatively, the free-living nematodes have not been studied much since they
4
Textbook of Introductory Plant Nematology
are not considered economically important. Most of these nematodes, especially those existing in fresh water and soil, are very minute. Marine forms such as Chaetostoma, Chromadora, Deontostoma etc. are specially adapted to live in salt waters. Species belonging to genera Plectus, Dorylaimus, Nygolaimus, Mononchus, Rhabditis etc. are common inhabitants of fresh water and soil. The soil forms may essentially be considered as aquatic since they live in a thin film of water around soil particles or water in the soil pores. Some of the free-living bacterial feeding soil nematodes e.g., Caenorhabditis elegans and C. briggsae have recently become the subject of intensive research by geneticists, cytologists, nutritionalists, physiologists and toxicologists, to understand some of the basic biological phenomena such as ageing (gerontology), genetic control of various life processes, cell lineage leading to organ formation, nutrition and physiology. The genome of Caenorhabditis elegans has been worked out. Brenner, Sulston and Horvitz received the Nobel Prize in Physiology or Medicine in 2002 for their work on the fate of individual cells (cell lineage pattern) and the role of genes in regulating development and apoptosis in this nematode. Caenorhabditis Genetic Center at National Institute of Aging, University of Missouri, Columbia, USA has been established that is responsible for maintenance of C. elegans genetic map, genetic nomenclature, storage, distribution of mutants. The simple genetic make-up of free-living bacteriophagous nematodes, ease of genetic manipulation (induced mutation), complete nervous system, mass culturing on synthetic media, short life-cycle, transparent cuticle, small size, storage in liquid nitrogen; are some of the characteristics which are being exploited for their use as biological models. Another free-living nematode, Panagrellus redivivus is being used as a biological indicator of pollution in toxic terrestrial and aquatic ecosystems.
Parasitic nematodes Parasites of human beings: The nematode parasites of human beings are known since ancient times because of their large size and severe ailments to mankind. Ascaris lumbricoides: The intestinal roundworm is the most common among people living in poor hygienic conditions, approximately 25% of the world population is infected with this nematode. The adults reach up to 40 cm in length, each female lays 2.7 million eggs per day in the faeces. It causes anaemia, and heavy infection may lead to intestinal blockage. Enterobius vermicularis: The pinworm, is parasitic in caecum and is about 1 cm long. These are commonly visible as wriggling worms in the faeces of children. These cause severe itching in the anal area, particularly while sleeping, when the female worms emerge through anus to lay eggs in the perianal area. Wucheraria bancrofti: The filarial worm is a parasite of lymphatic system causing inflammation of limbs and genital organs (Fig. 1.1). The disease is known as ‘elephantiasis’, and in India it is prevalent in the coastal areas of south India besides West Bengal, Bihar, Odisha and other eastern parts. The nematode is transmitted by mosquitoes.
5
Introduction
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Fig. 1.1 Some extreme cases of elephantiasis; A. of legs and feet, B. of scrotum and legs, C. of mammary glands (Source: Chandler & Read, 1960)
Onchocerca volvulus: Another filarial worm, the adults of which occur in the nodules of subcutaneous tissues (Fig. 1.2). It causes ‘onchocerciasis’ or ‘river blindness’ and is prevalent in Africa, central and south America and Yemen. It is transmitted by black fly, Simulium sp. Ancylostoma duodenale and Necator americanus: The hook¬ worms which infect about one quarter of world’s population, are common in Europe, North Africa and Asia. The Fig. 1.2 A nodule (arrow) caused by adults reside in intestinal mucosa and Onchocerca volvulus on the head each adult female can suck up to 0.2 of the host (human) in West Africa (Source: Poinar, 1983) ml blood daily, leaving a bleeding wound on the small intestinal wall. Dracunculus medinensis: The guinea worm, is a parasite of subcutaneous tissues. Approximately 50 million people in Africa and Asia are infected with this nematode. There is intense local pain when nematode emerges through blisters on limbs to release juveniles in water (Fig. 1.3). The ‘folk’ way of W
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Fig. 1.3 Guinea worm ( Dracunculus medinensis) infection in human beings. Top. a blister on the foot; Bottom, an adult worm partially emerged from the burst blister
Textbook of Introductory Plant Nematology
6
extracting the female is to catch it on a cleft stick and roll it on the stick (Fig. 1.4). The ‘fiery serpents’ which molested Israelites by the Red Sea were probably guinea worms.
Parasites of other vertebrates: The nematode parasites of vertebrates, mainly the domesticated animals and poultry, were discovered much early. These are easily visible to the naked eye, and some forms are common to human beings as well. Trichuris species: The whipworm, is about 30-50 cm long and is very commonly encountered in the colon, rectum and appendix of dogs, pigs and ruminants. Dioctophyma renale: The giant kidney worm, may reach up to 3 feet (90 cm) in length, is a parasite of dog, besides man. Haemonchus contortus: Is another common nematode parasite in the stomach of sheep, goat and cattle. It is a blood sucking nematode and causes anaemia in infected animals. Trichostrongylus spp.: Many species of this small nematode commonly parasitise the stomach of ruminants, horses, sheep and goats. Ascaridia galli: The common ascarid worm parasitic in the small intestine of chicken. Parasites of invertebrates: Among invertebrates, nematode parasites of insects are well known. Mermis nigrescens - a parasite of grasshoppers, and Romanomermis culicivorax - a parasite of mosquitoes (Aedes, Anopheles, Culex etc.), belong to mermithid group. The insects die shortly after the large
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7
Introduction
\ 1 A Fig. 1.5 Parasitism of a grasshopper by a mermithid nematode
nematodes leave the insect body (Fig. 1.5). These parasites have been used for the biological control of insects, particularly Romanomemis culicivorax against mosquitoes. Another group of microscopic nematodes belonging to genera, Steinernema (Fig. 1.6) and Heterorhabditis are unique in their ability to carry and release specific bacteria (Xenorhabdus and Photorhabdus spp.) inside the insect haemocoel, where they cause septicaemia and kill the insect host, and in turn provide nourishment for the developing nematodes in the insect cadaver. Some of these nematodes are being mass multiplied on artificial media and have been commercialised for the biological control of insects.
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Textbook of Introductory Plant Nematology
8
Parasites of plants: Plant parasitic nematodes are microscopic, mostly attacking roots (Fig. 1.7), but some forms specialise in parasitising aerial plant parts. Only a few examples are cited here, as they form the subject of this book in the ensuing chapters.
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Various types of tylenchid nematodes feeding on root tissues (Source: Siddiqi, 1986)
Anguina tritici: The seedgall nematode of wheat Meloidogyne spp.: The root-knot nematode of rice, vegetable, fruit, fibre and pulse crops Heterodera avenae: The cyst nematode of wheat, barley and oats Tylenchulus semipenetrans: The nematode parasite of all citrus group. Nematodes are morphologically and physiologically adapted to live in diverse habitats. Consequently, different groups of scientists have emerged who specialise in dealing with different types of nematodes. The free-living forms are usually studied by Zoologists, parasites of animals (livestock, poultry) by Veterinary Parasitologists, parasites of human beings by Human Parasitologists or Helminthologists, parasites of insects by Insect Pathologists, and parasites of plants by Plant Nematologists or simply Nematologists.
PHYTO-NEMATOLOGY By convention ‘Nematology’ refers to only Plant Nematology or Agricultural Nematology or Phytonematology, and deals with those forms of nematodes which parasitise plants and are of economic importance to agriculture, horticulture and forestry. Compared to human and animal parasitic
Introduction
9
nematodes, the plant parasitic nematodes were discovered much later. The first plant parasitic nematode was recorded in 1743, later on named as Anguina tritici.
Although plant parasitic nematodes were long being suspected as limiting factors in agriculture, their economic importance was not recognised until the middle of twentieth century. These can be attributed to microscopic size; hidden mode of life, either in soil or roots; absence of clear-cut symptoms on plants; and lack of trained personnel. After 1940s, however, when the experimental evidence proved the damaging potential of phytonematodes to crops beyond doubt, this discipline has grown very fast. Numerous nematode diseases of agricultural and horticultural crops have been discovered in temperate as well as tropical regions of the world. Nematology now stands as an independent branch of plant protection, at par with Entomology, Plant Pathology and Weed Science.
Economic importance of nematodes to agriculture Plant parasitic nematodes are ubiquitous and more than 1,800 species have been recorded so far. They parasitise all types of plants - from algae to trees. A handful of soil from around the roots of any plant would yield hundreds of plant parasitic nematodes belonging to at least 4-5 genera. Being obligate parasites, they must draw their nutrition from plant hosts, which in turn debilitate the plant to some extent. The extent of direct damage by the nematodes to plants depends on several factors. These include - nematode density in soil, nature of parasitism (ectoparasite, endoparasite), host susceptibility, cropping pattern, edaphic factors (soil texture, moisture etc.), and ambient climatic conditions (mainly temperature). Nematodes, by themselves, rarely kill the plants in order to ensure their own survival. However, in nature, they are involved in all sorts of interactions with other microorganisms (fungi, bacteria, viruses) leading to disease complexes, in which nematodes may play the role of incitant, aggravator, vector or predisposer (indirect damage) of plants to secondary attack by other plant pathogens. The economic importance of a plant parasitic nematode is judged by its parasitic or pathogenic potential, geographical distribution, and value of the crop. It is very difficult to estimate the extent of losses inflicted by nematodes to the crops. Crop loss assessments due to nematodes are usually based on field trials involving the use of nematicides. The increase in crop yield following nematicidal treatments compared to untreated plots is usually related to that
avoided by nematode control. Quite frequently, crop loss estimates are also expressed as per cent reduction in yield in relation to nematode density, which is highly heterogenous even in a single field. Further, our knowledge about nematode problems, particularly in the developing countries many of which lack trained nematologists, is still meager. Nematode problems from such areas which mostly lie in the tropical and subtropical zones, are likely to be more damaging and varied, considering highly conducive climatic conditions for nematode development and poor crop husbandry in these countries. Several crop loss estimates have been made on a world wide and individual
10
Textbook of Introductory Plant Nematology
country basis, particularly in the developed countries. The most authentic and widely quoted estimates on crop losses due to plant parasitic nematodes were provided by Prof. J.N. Sasser, who led an International Meloidogyne Project during 1980s. His estimates are based on the response to questionnaires he sent to leading nematologists all over the world. Overall average annual loss of the world’s major crops due to damage by plant parasitic nematodes was estimated to be 12.3%. For the 20 major crops which serve as the man’s primary food source, annual yield loss of 10.7% was estimated, while for another group of 20 crops mainly of commercial importance, a 14% annual yield loss was assessed (Table 1.1). Developing countries had a crop loss figure of 14.6% compared to 8.8% in developed countries, when estimated losses for all the 40 crops were considered. Monetary losses due to nematodes on 21 crops were estimated at US $ 77 billion annually based on 1984 production figures and prices. According to a report of 1971, in USA alone, nematodes are known to cause 6% loss in field crops ($ 110 million per year), 12% loss in fruits and nuts ($ 225 million per year), 11% loss in vegetables ($ 267 million per year), and 10% loss in ornamentals ($ 60 million per year). In India, national loss in 24 different crops has been estimated to the extent of ? 21,068.73 million based on minimum support price (MSP) of 2005. Earlier, Table 1.1 Estimated annual yield losses due to damage by plant parasitic nematodes world wide Life sustaining crops
Banana Barley
Cassava Chickpea
Coconut Com/Maize Field bean Millets
Oat Peanut Pigeonpea
Potato Rice Rye Sorghum Soybean Sugarbeet Sugarcane Sweet potato Wheat Average
Loss (%) 19.7 6.3 8.4 13.7 17.1 10.2 10.9 11.8 4.2 12.0 13.2 12.2 10.0 3.3 6.9 10.6 10.9 15.3 10.2 7.0 10.7
Economically important crops
Cacao Citrus Coffee
Cotton Cowpea Brinjal
Forages Grape Guava Melons Misc. others * Okra Ornamentals Papaya Pepper Pineapple Tea Tobacco Tomato
Yam Average
Loss (%) 10.5 14.2 15.0 10.7 15.1 16.9 8.2 12.5 10.8 13.8 17.3 20.4 11.1 15.1 12.2 14.9 8.2 14.7 20.6 17.7 14.0
Overall average 12.3%
'Additional miscellaneous crops of economic importance, especially for food or export
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