Indian Journal of Social and Natural Sciences Indian J. Soc. Nat. Sci. ISSN: 1(1): 1-16 (2011) © Raiganj- Gour Banga Research Forum, Raiganj, India

Review Article Nematode pests of crops in West Bengal, India Matiyar Rahaman Khan * Department of Agricultural Entomology, Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia 741 235, West Bengal, India * e-mail: mrkhanbckv@rediffmail.com Abstract: Plant parasitic nematodes (PPNs) are popularly known as the ‘hidden enemy’ of crops for their characteristic nature of damage. Economically important phytonematodes such as of root knot, foliar, rice stem, root lesion, reniform, rice root and citrus nematodes are documented along with the characteristic symptoms and the crops affected in West Bengal. Some of the dreaded species like Globodera rostochiensis, G. pallida, Anguina tritici, Radopholus similis, Heterodera cajani, Ditylenchus myceliophagus, Aphelenchoides composticola are known to have potential impact on important crops in other states of India but their occurrence in West Bengal is either limited or not known. Further, PPN acts as predisposing agent in the development of disease complexes with fungi, bacteria and viruses as resistance breaking agents. Nematode diversity in jute, rice, ginger, banana, guava, pineapple, arecanut, coconut etc. and in other soil environment has been known from West Bengal. PPN feed on plants causing injury and through secretion, modify the host tissue into specialized nutritive cells as multinucleate giant cells, syncytium or nurse cells for ensuring permanent feeding. Field diagnosis of nematode problems in major crops of West Bengal are given along with their management options. Ectoparasitic nematodes are abundant in soil but little attention is given for their pathogenic importance to crops. Foliar nematode in tuberose in West Bengal and Orissa and rice root-knot nematode in rice nursery and systems of rice intensification are emerging nematode pests in India. Reniform nematode is widespread in West Bengal and frequently encountered in various crops, however, little attention is given by the growers for its non-specific damage symptoms. Key words: Plant parasitic nematode pests, diversity, distribution, symptoms, management, field diagnosis, West Bengal Plant parasitic nematode (PPN), the farmers’ ‘hidden enemy’ of crops is one of the most harmful organisms which depend on plants for their survival and multiplication. Soil ecosystem supports huge population of diverse feeding groups of nematodes but only a fraction of that population establishes parasitic relationship with plants. Majority of soil inhabiting nematodes are free-living and they play a beneficial role in the soil system. Parasitic nematodes can cause damage to almost all kinds of crops; however, due to their subterranean habit, microscopic size (from 0.3 to 10 mm length), they are

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often invisible to the naked eye. They penetrate and feed on the root of growing plants, stealing nutrients vital for plant growth and exposing the roots to attack by other soil pathogens. It has been widely recognized that plant parasitic nematodes constitute one of the most devastating pest groups and are responsible for insidious disease symptoms in different crops causing huge losses. Estimated annual yield loss in the world’s major crops due to PPNs is about 12.3% and it is about 14% in the developing countries (Sasser and Freckman, 1987). According to Jain et al. (2007), nematode is responsible for loss in 24 crops to the tune of Rupees 21.07 billion every year in India (one US $ = ± Rupees 45). Beside direct damage, PPNs act as predisposing agents in development of disease complexes caused by fungi, bacteria and viruses. In many situations, plant varieties resistant to fungi and bacteria are rendered susceptible in the presence of nematodes. There is no doubt that nematodes either alone or in concert with other pathogens cause considerable yield loss. In a modern crop production system, intensive and extensive cultivation of crops particularly in irrigated system has seriously aggravated nematode problems in various crops. The hidden nature of nematodes, causing damage out of sight of the farmers and scientists and non-specific disease symptoms in the above ground parts of the crops are possible reasons for which they have been given little attention as a potential pest of crops. Nematode diversity and distribution in West Bengal Soil ecosystem supports a large diversity of soil nematode fauna and a small fraction of them establishes parasitic relationship with crops and causes yield loss. Plant parasitism in nematodes has evolved in three out of 18 orders: Tylenchida (class: Secernentea), Aphelenchida (class: Secernentea) and Dorylaimida (class: Adenophorea). The stylet-bearing nematodes belonging to the order Tylenchida are most damaging to crops and adequate attention has not been given to identify the species associated with the crops. In India, so far 600 species under this order have been identified, of which 67 species (11%) are from West Bengal. Another important order, Aphelenchida is represented by 70 species from India, of which only seven (10%) are recorded from West Bengal. Some long stylet-bearing nematode belonging to the order Dorylaimida are ectoparasites of many horticultural and agricultural crops and are potential vectors of plant viruses. Of the 500 species of this order recorded in India, 81 species (16%) have been identified from West Bengal. Some ectoparasitic nematodes and vectors of plant viruses belonging to the order Triplonchida are represented by 15 species in India; only two species of which are known from West Bengal. About 70 species of the order Mononchida (include predatory nematodes) are known from India; only 15 species (21%) among them have been recorded in West Bengal (Baqri, 1999). Chaturvedi and Khera (1979) described nematodes belonging to 42 genera, of which 33 genera were associated with jute in West Bengal. Nineteen species of PPNs within 13 genera were reported from five tea estates and plantations, showing heavy decline in production in Darjeeling district of West Bengal. Helicotylenchus dihystera was

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dominant followed by Macroposthonia ornata, Pratylenchus loosi, Meloidogyne brevicauda, Helicotylenchus sp. and Paratylenchus lepidus. H. erythrinae, P. lepidus, P. loosi, Atlantadorus porosus, Aglenchus agricola and Coslenchus sp. were associated with tea (Mukherjee and Dasgupta, 1982). Rama and Dasgupta (1998) investigated PPNs belonging to 8 genera and 10 species associated with ginger. The most economically important species found were R. reniformis, H. indicus and Xiphinema elongatum while R. reniformis, P. coffeae and H. multicinctus showed the greatest prominence values. Rama and Dasgupta (2000) undertook an ecological study of PPNs associated with coconut and arecanut in Darjeeling, Jalpaiguri and Cooch Behar districts of West Bengal and the nematode species found were P. coffeae, P. brachyurus, H. elegans, H. mucronata, Ditylenchus triformis, Criconemella onoensis, Nothotylenchus acutus and M. incognita in the descending order of importance. The nematode species viz, Scutellonema brachyurum, R. reniformis and H. elegans were considered important in coconut while in arecanut, R. reniformis, Hoplolaimus seinhorsti and Meloidogyne spp. were the important nematode species. Twelve species of 10 plant parasitic genera identified from guava rhizosphere of West Bengal were M. incognita, M. javanica, M. graminicola, P. coffeae, P. brachyurus, Hoplolaimus indicus, Rotylenchulus reniformis, H. goodi, H. indicus, H. abunaamai, Tylenchorhynchus mashhoodi and T. nudus (Khan et al., 2007). Seventeen species of PPNs viz. P. coffeae, P. brachyurus, P. similis, M. incognita, M. javanica, Hoplolaimus indicus, R. reniformis, H. multicinctus, H. abunaamai, H. incisus, H. gratus, H. dihystera, T. nudus, T. mashhoodi, T. coffeae, Hirschmanniella mucronata and Criconemoides sp. were identified from banana rhizosphere in West Bengal (Khan and Hasan, 2010). An updated distribution map (Khan et al., 2010) of major plant parasitic nematode infecting various crops in West Bengal is given in Figure 1. In this review, only economically important plant parasitic nematode problems of crops (Tabs 1 and 2) in West Bengal, diagnostic damage symptoms on major crops (Tab. 3) and their management options (Tab. 4) are briefly discussed. Nature of nematode problems PPNs can be detrimental to crop growth and development depending on population density and host susceptibility. Generally, they feed on the host tissues with the help of their protrusible stylet causing injury to plant tissue, and due to feeding and secretion, modify the host tissue into specialized nutritive cells as multinucleate giant cells, syncytium or nurse cells for ensuring permanent feeding. Some nematodes induce gall formation on the plant’s root, leaf and seed. The feeding of plant nematode on tissue develops lesion and subsequent discolourations. Infected plants are easily attacked by various soil pathogens like bacteria, fungi and develop a disease complex/diseases syndrome. The etiology of those diseases caused by the organisms involved is difficult to determine. Several nematodes serve as vector of plant viruses. Thus nematodes indirectly act as plant pathogen, predisposing agent and vector of plant viruses. Plant

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parasitic nematodes are known to interfere with the activity of beneficial nitrogen fixing Rhizobium bacteria in leguminous crops.

Figure 1. Distribution of major plant parastic nematodes infecting crops in West Bengal.

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Table 1. Plant parasitic nematodes of high economic importance in West Bengal. Nematodes Species Diseases Crops References

Root knot nematodes

Meloidogyne incognita, M. javanica, M. graminicola

Root gall Vegetables, oilseeds and pulses, fruits, tea, betelvine, jute, ginger, rice, mulberry

Chattopadhyay and Sengupta (1955); Sen and Dasgupta (1976a,b); Dutt and Saha (1975); Mukherji and Sharma (1973); Pal and Jayaprakash (1983); Singh and Khera (1980); Das et al. (1990); Khan (2001); Sukul and Sen (1989); Khan and Murmu (2004); Khan et al. (2004a,b); Khan (2005a,b); Chandra and Khan (2011)

Foliar/white tip nematode

Aphelenchoides besseyi

Floral malady/ Foliar white tip disease

Tuberose, rice Chakraborti and Ghosh (1993); Khan et al. (1999); Khan (2001a); Khan (2004c); Khan and Feza Ahmad (2002); Das and Khan (2007)

Rice stem nematode

Ditylenchus angustus

Ufra Rice Chakrabarti et al. (1985); Rao et al. (1986a, 1986b); Prasad et al. (1987, 1992)

Rice root nematodes

Hirschmanniella oryzae, H. mucronata

Root lesion

Rice Ahmad et al. (1984); Bala and Khan (2002); Khan and Bala (2003)

Citrus nematode

Tylenchulus semipenetrans

Slow decline

Citrus Das and Mukhopadhayay (1981); Dasgupta et al. (1985a); Thapa and Mukhopadhyay, (1994)

Lesion nematodes

Pratylenchus coffeae, P. indicus, P. zeae, P. brachyurus, P. loosi

Root lesion

Rice, jute, banana, pineapple, wheat, fruits, tea plantations, ginger, pulses, forage, fodder and grains legumes

Mukhopadhyay and Haque (1974a,b); Mukherjee and Dasgupta(1981a,b); Dasgupta et al. (1985a,b); Rama and Dasgupta (1987, 1998); Mishra and Sasmal (1988); Chaturvedi and Khera (1979); Khan (2005a)

Reniform nematode

Rotylenchulus reniformis

- Vegetables, pulses, ginger, banana, pine apple, betelvine, tuberose, oilseeds and fibres

Mukherjee and Dasgupta (1981b); Mukherjee and Dasgupta (1983a,b); Rama and Dasgupta (1987, 1998); Sukul and Sen (1989); Khan and Pal (2001); Khan (2005a); Khan (2006a); Anonymous (2006); Chandra and Khan (2011)

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Table 2. Nematodes of high economic importance but not known in West Bengal. Nematodes Scientific names Crops References

Potato cyst nematodes Globodera pallida, G. rostochiensis

Potato, tomato, brinjal -

Pigeon pea cyst nematode1 Heterodera cajani Pigeon pea Ganguly and Dhawan (1998); Khan (2005b)

Burrowing nematode Radopholus similis Banana, coconut, arecanut, black pepper

-

Wheat seed gall nematode Anguina tritici Wheat - Cereal cyst nematode Heterodera avenae Barley - Rice cyst nematode2 Heterodera oryzicola Rice, banana - Mushroom nematodes Ditylenchus myceliophagus,

Aphelenchoides composticola

Edible mushrooms

1. Limited information available from West Bengal 2. Occurrence of the species has not been further confirmed

Table 3. Nematode problems of crops and their symptoms in West Bengal. Name of the nematodes/diseases Nature of damage symptoms Crops

affected

1. Root-knot nematodes (M. incognita and M. javanica)

Infection of root-knot nematode produces characteristic disease symptoms on the below ground root system popularly known as ‘root gall’ or ‘knotted roots’. The size of galls also differs with the level of infection as in case of heavy infection, large size or multiple galls or secondary galls develop. Besides galling, forking of taproot in carrot and tubercle on potato tubers are also noticed. Above ground symptoms are non-specific in nature. Infected plants exhibit symptoms of general mineral deficiency, yellowing, stunting, wilting during hotter part of the day, chlorosis, premature shedding of leaves and poor look of plants resulting in low yield. The nematodes are also involved in interaction with other soil borne fungi, bacteria, and viruses and cause serious damage to crops. Most common interaction of root-knot nematode with Ralstonia (=Pseudomonas) solanacearum is causing “Pseudomonas wilt” in tomato, brinjal and potato.

Vegetables, oilseeds and pulses, fruits, fibres, tea, betelvine, ginger and flowers

2. Rice root-knot nematode (M. graminicola)

Above ground symptoms are non-specific in nature as yellowing, stunting of foliage, delayed flowering by 10 to 15 days and reduced number of tillers. The presence of characteristic ‘hook shaped’ or ‘ring-like’ root gall on the root tip of growing rice seedlings is the confirmatory evidence for the association of this nematode. Galls produced by the nematode induce growth of lateral rootlets and root hairs.

Rice

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Name of the nematodes/diseases Nature of damage symptoms Crops

affected 3. White tip disease

(A. besseyi)

It is easy to detect the presence of nematode within the rice seeds. In the field, the initial appearance of symptoms as the leaf tip (up to 5 cm) becomes pale yellow or whitish at tillering stage and subsequently, the leaves get dry. These symptoms are found for a short period in the plant. The tip of the flag leaf are often twisted which may obstruct the emergence of panicles. Infested panicles are shorter and lighter in weight as compared to healthy panicles.

Rice

4. Tuberose floral malady (A. besseyi)

Infected flower stalk initially appears rough, stalk becomes crinkled, stunted and finally distorted and in severe cases flower buds fail to bloom. Brown streaks appear on leaf bracts and petals and subsequently develop rusty brown spots. The severely infected flower stalk becomes rotten and brittle over drying, even get blind. The number of flowers per stalk is also reduced and small crinkled and distorted flowers are produced which are not acceptable in the market. The nematode, A. besseyi remains in masses forming ‘nematode wool’ which could be easily recovered from dark brown spots (Khan and Pal, 2001).

Tuberose

5. Rice root nematode (Hirschmanniella spp.)

The above-ground symptoms are non-specific as stunted growth, leaf chlorosis, reduced tillering and delayed flowering. The juvenile and adult stages penetrate through entire length of roots and feed on cortical cells leading to the formation of channels or cavities in the roots. Feeding sometimes extends to central vascular regions. The infected roots exhibit water-soaked brown lesions which are mostly spindle shaped. The physiological function of infected plants is disrupted and plant growth is reduced.

Rice

6. Citrus nematode (T. semipenetrans)

Nematode is one of the causal factors for ‘slow decline’ in citrus’ which is characterized by general reduction of tree growth, lack of vigour, yellowing of foliage and small size of fruits. The nematode is semi-endoparasite of citrus root. It causes symptoms that are often non-descriptive and difficult to diagnose. The nematode is often unnoticed in the seedlings in nursery which causes widespread distribution. The presence of the nematode is best confirmed by microscopic observations of soil and root samples. The female nematodes and their gelatinous matrix containing eggs with adhered soil particles give the roots a dirty appearance which is not easily washed off. The most serious effects of the nematode on the growth and yield of citrus are usually encountered when new seedling are planted on old orchard. This condition is known as ‘citrus replant problem’. The young tree grows slowly and fruiting is delayed. This condition of infested trees is referred to as ‘slow decline’ which implies general deterioration of citrus trees beginning with production of smaller and fewer fruits. The extent of decline in mature trees is related to their vigour, tolerance to the nematode and to the degree of infection. The nematode feeds on surface layers of roots causing discolouration and necrosis.

Citrus

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Name of the nematodes/diseases Nature of damage symptoms Crops

affected

7. Reniform nematode (R. reniformis)

Symptoms of damage to crops are non-specific on the above ground or even in the below ground parts necessitating a close observation to confirm their presence and damage. It feeds on cortical tissue, phloem and pericycles and its infection may cause necrosis in roots of certain crops. Symptoms appear as root discolouration, shedding of the leaves and formation of malformed fruits and seeds. In addition to causing direct damage to plants roots, the nematode in concert with other pathogens like Fusarium spp., Verticillium spp., Sclerotium rolfsii and Rhizoctonia solani develop disease complexes. It has also been reported to parasitize the bacterial nodules.

Papaya, jute, cowpea, tomato, cotton, castor, banana, betelvine, tuberose, etc.

8. Root lesion nematodes (Pratylenchus spp.)

Above ground symptoms caused by these nematodes are non-specific in nature. The group usually infects roots, rhizomes or tubers. Having penetrated into roots, they multiply in large numbers. All the life stages of this group are infective. The attacked plant’s root exhibits dark red brown lesions caused by necrosis of the invaded cells. Root lesion is the most characteristic symptom. The lesions initially appear as small elongate, water-soaked spots which soon turn brown to black. Loss of primary roots, pruning or decay of roots, reduced size of blossoms, shrinking of grains are also associated with the nematodes. Several secondary soil borne fungi, bacteria are also involved for rotting and decay of roots and thus normal functioning of infested roots is heavily impaired.

Banana, tea, rice, jute, ginger, pulses and vegetables

Table 4. Crop-wises nematode management options (updated from Khan, 2004b). Crop Nematode species Management options

Jute Root-knot nematode (Meloidogyne spp.)

i) Removal and safe destruction of stubbles. ii) Vegetables-jute rotation should be avoided. Jute-wheat/mustard

crop sequence is nematode suppressive (Khan and Banerjee, 2003).

iii) Before sowing, seed treatment with carbosulfan, such as Marshal 25ST at 3% w/w is found effective (Khan, 2004a).

Rice Rice root nematode and Rice root-knot nematode

i) Nursery bed treatment with carbofuran 3G at 0.3 g a.i./m2 followed by main field application of carbofuran 3G at 1 kg a.i./ha at 40 days after transplanting (Jain et al., 2010).

White tip nematode (Aphelenchoides besseyi)

i) Rice stubble to be burnt or destroyed ii) Sun-drying of rice seed on concrete floor on bright sunny days at

least for six consecutive days, for four hours/day. iii) Soaking rice seeds in plain water (1:2 v/v) for overnight followed

by adding double volume of boiling water for 10 min and drying of seeds in shade (Kuriayan, 1995).

iv) Seed soaking in carbosulfan (Marshal 25EC) at 0.1% for 12 h (Rao et al., 1986a).

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Crop Nematode species Management options

Tuberose Foliar nematode (A. besseyi)

i) Pre-soaking of bulbs for overnight followed by hot water treatment at 500C for 20 min (Khan et al., 2005, 2006) or dipping of bulbs in monocrotophos 36SL at 750 ppm for 6 h (Khan et al., 2008).

ii) Three to four sprayings with monocrotophos 36SL at 500 ppm at 15-20 days interval (DI) starting at sprouting from bulb.

iii) During peak flowering stage additional spraying with NSKE 5% at 15 DI may be advocated.

iv) Infested plant parts should be burnt immediately on inspection. v) Growing nematode tolerant cultivars (Prajwal, Shringar, Phule

rajani). vi) Run-off or irrigation water from infested field should not be allowed

to enter the uninfested tuberose fields (Khan, 2006b).

Vegetables Root-knot nematode (Meloidogyne spp.)

i) Raising nematode-free seedlings: Seed soaking with carbosulfan 25EC at 0.1% or seed dressing with carbosulfan (Marshal 25DS) at 3%w/w was found effective.

ii) Crop rotation with non-host crops like mustard, sesame, maize etc. helps to reduce soil nematode population.

iii) Use of farm compost or FYM or concentrated organic manures like neem, mustard, mahua, karanj cakes either as broadcasting or pit application is effective against nematode.

iv) Growing nematode resistant varieties, if available. v) Nursery-bed treatment with carbofuran 3G at 0.3 g to 0.6 g a.i./m2

for raising nematode free seedlings. vi) Bare dipping of root with systemic nematicides like carbosulfan

25EC, or cartap hydrochloride 50WP at 0.05 to 0.1% for 1 to 6 h. vii) Vine dipping of pointed gourd into carbosulfan 50EC at 0.05 to

0.07 % for 6 h. viii) Antagonistic like marigold, mustard, sesame, either in crop rotation

or as inter crop/mixed crop. ix) Using biocontrol agents (BCAs) like Paecilomyces lilacinus

(Bionematon, Yorker), Pseudomonas fluorescens at 20 g/m2 or Trichoderma spp. either in nursery or mix with well decomposed FYM (incubate 1 kg BCA in 100 kg FYM for at least two weeks) for effective control of root knot nematodes.

Betelvine Root-knot nematode, Reniform nematode (Rotylenchulus reniformis)

New Betelvine Orchard: i) Soil application of carbofuran 3G (Furadan) at 1.5 kg a.i./ha at

planting of vines. ii) Organic manuring with FYM at land preparation and neem cake at

200-400 kg/ha in 2 to 3 split doses. Old Betelvine Orchard: i) Application of neem, karanj, ground nut at 1ton/ha or poultry

manure at 2 ton/ha. ii) Using BCAs like Paecilomyces lilacinus at 10 g/pit in combination

with carbofuran at 0.75 kg a.i./ha.

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Crop Nematode species Management options

Mandarin Orange

Citrus nematode (Tylenchulus semipenetrans)

Prophylactic Measures: i) Nursery raising of seedlings free from nematode infection. ii) Previously infested citrus orchard should be destroyed and burnt

or fumigated. Curative Measures : i) Application of oilcakes of neem, mahua, groundnut etc. 1 kg/plant. ii) Intercropping with marigold, garlic, onion in citrus orchard. iii) Combined use of neem cake at 1kg/plant along with carbofuran

3G 1.0 kg a.i./ha or 100 g Furadan or Thimet/tree twice a year (Thapa and Mukhopadhyay (1994).

iv) Use of resistant ‘trifoliate’ citrus stock.

Field diagnosis of nematode problems in crop plants A. Above ground field symptoms a. Stunting growth, reduction of foliage and progressive decline of plants b. Yellowing (chlorosis) of leaves c. Leaf with angular spots and necrosis, white tip d. Wilting of plant in hot sunny days e. Early senescence f. Poor yield g. Reduction in number of tillers in rice h. Deformed or distorted foliage (crinkling, curling and twisting), earhead, panicles,

flowers (floral malady), grains i. Formation of seed gall, stem gall or leaf gall B. Below ground symptoms a. Root knot or root gall, swelling of root tip, forking, branching or stubbed/

abbreviated root b. Root lesions or brown/black spots, root discolouration c. Lesion or deformation on tubers, rhizomes etc. d. Dirty root with soil adhered to surface (modified after Jain et al., 2010) Root-knot nematodes (Meloidogyne spp.) Root-knot nematodes (Meloidogyne spp.) are one of major concerns for profitable cultivation of crops. These have very wide distribution and cause serious damage to all kinds of vegetables, pulses, fruits, plantation crops etc. The average global yield loss is about 5% and could be more in the tropics and sub-tropics (Taylor and Sasser, 1978). Till date, of the 100 known species of root-knot nematodes, only 14 species of Meloidogyne are recorded in India, and only four species – Meloidogyne indica, M. lucknowica, M. triticoryzae and M. piperi have been described exclusively from India. In West Bengal, Chattopadhyay and Sengupta (1955) recorded for the first time a root-knot nematode, M. incognita infecting jute. Chaturvedi and Khera (1979) recorded the

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occurrence of M. incognita and M. javanica in jute in West Bengal. The occurrence of root-knot nematodes species like M. incognita, M. javanica and M. arenaria on some crop plants was recorded in Sriniketan (Sen and Dasgupta, 1976a,b). The most predominant species of root-knot nematodes are M. incognita, M. javanica, M. arenaria and M. hapla. Four races (designated as 1, 2, 3 and 4) of M. incognita are known to be present in India, but in West Bengal, only race 2 and race 3 were identified (Khan, 2001b). Race 2 is prevalent in southern Bengal and race 3 in northern Bengal (Khan and Murmu, 2004). Root-knot nematodes are one of the potential constraints for cultivation of vegetables, particularly in alluvial tracts of West Bengal. Vegetable crops harbour large number of plant parasitic nematodes, but root-knot nematodes are the most damaging one. They affect the crop directly and indirectly by interaction with various soil-borne fungi, bacteria and viruses. All the species of root-knot nematodes produce characteristic ‘root gall’ or knotted root symptoms, which could be easily recognized by the naked eye. There is hardly any vegetable crop which is not attacked by the root-knot nematodes. Several crops like onion (Khan, 2003a), balsam (Khan, 2003b), beet root, cabbage, potato, amaranthus etc. are currently under the threat of root-knot nematodes in West Bengal. Therefore, these are widely considered as a limiting factor for cultivation of vegetables. The lack of awareness among the farmers about the nematode problems and non-availability of suitable package of practices to extension workers for managing the root-knot nematodes are the major hindrances for protecting the vegetable crops from root-knot nematodes. Chemical approach of nematode management is no doubt effective but high doses of nematicides required for managing nematodes are neither economical nor environmentally safe. Ectoparasitic nematodes Several ectoparasitic nematodes are emerging as new problems of crops. In spite of being numerous and having much adaptive biological features for survival and multiplication as compared to endoparasites, they are regularly ignored (Khan and Ganguly, 1995). Many genera like Tylenchorhynchus, Hoplolaimus, Helicotylenchus, Paratylenchus, Hemicriconemoides, Hemicycliophora, Criconemoides, Xiphinema, Longidorus, Trichodorus etc. are prevalent in the rhizosphere of agricultural, horticultural and forest crops: their pathogenic potential have been proved and their damaging nature are well documented. The occurrence of T. brevilineatus in groundnut (kalahasty disease) in Andhra Pradesh (Reddy et al., 1984) and tobacco in Gujarat, rice crop failure due to Hoplolaimus indicus in West Bengal (Banerjee and Banerjee, 1966) and T. brassicae in cabbage and cauliflower have been reported. However, ectoparasitic nematodes are given very little attention because their symptoms induced in plants are not easily convincing and often confused with other soil problems and soil pathogens. The role played by this group of nematode is much more dangerous particularly when they interact with other soil microorganisms and thereby make the plants vulnerable to weak pathogens. In modern agricultural system, intensive and extensive cultivation of the same crop, changes in cultivation practices like high yielding

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varieties, poor organic nutrition in soil, indiscriminate use of agrochemicals etc. have resulted in a shift in this group’s pest status. Emerging nematode problems in West Bengal Root-knot nematodes (Meloidogyne spp.) are widely known as potential pests of diverse crops; however, some other nematode species are recently becoming threat in cultivation of crops. Chakrabarti and Ghosh (1993) recorded a floral malady problem in tuberose from Ranaghat area of Nadia, West Bengal. Tuberose foliar nematode (A. besseyi) inducing floral malady in Calcutta double and Calcutta single cultivars is now one of the limiting factors for cultivation of tuberose in West Bengal and this has been investigated over a decade. The management approaches for floral malady problem in tuberose has been stated in Table 2, however, it is one of the great concerns for the growers of West Bengal and Orissa. The rice root-knot nematode, M. graminicola is emerging as a nuisance in rice nursery and in the system of rice intensification (SRI) in West Bengal. M. graminicola, which was earlier found in pockets in the states of West Bengal (Mukhopadhyay and Khan, 2000), Orissa, Assam and Kerala, has now spread to newer areas of eastern Uttar Pradesh, Delhi, Haryana, Punjab, Himachal Pradesh, Tamil Nadu, Karnataka, Orissa, West Bengal and recently to Gujarat as per the reports from various cooperating centres of All India Coordinated Research Project (AICRP) on nematodes. The distribution of M. graminicola and its major hot spot areas in different parts of India identified by the cooperating centres of AICRP (Nematodes) has been well documented in a nematode distribution atlas by Khan et al. (2010). Pal and Jayaprakash (1983) reported this nematode species from the rice varieties IET2233, IET1444, and CNM25 grown at seed farms in Islampur and Chopra and in some standing crops in farmer fields in Balurghat and Tapan block of erstwhile West Dinajpur district of West Bengal. This nematode has many alternative hosts including weeds (Khan et al., 2004). The changing climate and growing conditions have probably provided congenial environment for survival and multiplication of the nematode species. Some of the SRI fields in Nadia district showed increased root-knot nematode infestation as compared to previous years of traditional rice crop. The system of rice cultivation is shifting from traditional method to SRI practice as a consequence of which a new ecological condition is being created which is probably favouring the nematodes. SRI practice includes planting younger and tender seedling, creation of greater aeration in soil and regulation of irrigation; all these have resulted in increased weed infestation. The altered niche provides a congenial situation for increased infestation of rice root-knot nematode. A semi-endoparasite, reniform nematode (R. reniformis) is widespread in West Bengal (Anonymous, 2006) and it is frequently encountered from the rhizosphere of various crops. Next to root-knot nematode, this nematode species occupies the second position in terms of its pathogenic potential to crops. However, little attention is given by the growers for its management.

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References Ahmad, N., Das, P.K. and Q.H. Baqri. 1984. Evaluation of yield losses in rice due to Hirschmanniella

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