Dr. M. R. Khan
Department of Agricultural Entomology
Bidhan Chandra Krishi Viswavidyalaya,
Kalyani, Nadia-741235, West Bengal, India
Email: mrkhanbckv@rediffmail.com
Introduction
Plant parasitic nematode, the hidden enemy of crops is one of the many groups of harmful organism which depend on plants for their survival. Nematode 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 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 widely been recognized that plant parasitic nematodes constitute one of the most devastating pests groups and are responsible for insidious disease symptoms in different crops causing huge losses. Estimated annual yield losses in the world’s major crops due to plant parasitic nematodes is about 12.3% and it is about 14% in the developing countries (Sasser & Freckman, 1987). In India, recent estimate showed nematode is responsible for both quantitatively and qualitatively yield losses amounting about Rs.240 billion every year (Sehgal & Gaur 1999). Beside direct damage, plant parasitic nematodes serve as predisposing agents in development of disease complexes with fungi, bacteria and viruses. In many situations, plant varieties resistant to fungi, bacteria are rendered susceptible when parasitized by nematodes. There is no doubt that nematodes either alone or in combination with other pathogens constitute an important constraint to world food production. Intensive and extensive cultivation of crops particularly in irrigated crop production system has seriously aggravated nematode problems in various crops. The hidden nature of nematode causing damage out of sight of farmers, scientists and non specific disease symptoms in the above ground parts of the crops are perhaps main reasons why so little attention has been given to the hidden pest of crops.
Management of plant parasitic nematodes with the use high doses of DD, EDB, DBCP etc. had been found promising, though did not receive much popularity. Moreover, all the effective chemicals have been withdrawn from world market due to their harmful effects on environment. Subsequently, efforts have been made to search for newer chemicals among the group of non-fumigants but failed to achieve the effective control as that of fumigants. In fact, nematodes are comparatively hardy animals require high doses of insecticide having nematicidal property. The growers are still dependent on the limited number of insecticides only because of non-availability of true and effective nematicides. With the increasing concern on environment, various alternative pest control methods like cultural, physical and biological control methods and botanicals are being tried to reduce the nematode damage of crops. However, judicious use of chemical nematicides could be applied for protection of many crops. Integration of various available practices is one of the current approaches for managing pest problems of crops. Cultural practices are known from time immemorial as a multiple pest control strategy. Biopesticides of botanical origin have also been proved as effective alternative of nematicides (Mishra, 2002).
Therefore, current options for nematode management are cultural practices, physical methods, biointensive nematode suppression, botanicals and sensible use of chemical nematicides.
Considering importance of nematodes in the integrated pest management system, following low input plant protection technologies viz. summer ploughing, soil solarization, organic manuring, crop rotation, adjusting dates of sowing, growing resistant varieties, irrigation management, optimum fertilization, hot water treatment, clean cultivation, green manuring, inter/mixed cropping, judicious use of pesticides, integration of two or more above mentioned methods (Gaur &Khan,1995) could be adopted for managing insect pest, diseases including nematodes in the crop production system.
Nature of nematode problems
Plant parasitic nematodes 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 plants injury and due to feeding and secretion modify the host tissue into specialized nutritive cells as multinucleate giant cell, syncytium or nurse cells for ensuring permanent feeding. Some other nematodes induce gall formation on plant’s root, leaf and seed. While feeding on plant tissues, develop lesion as a result of cell death 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 nematode functions as plant pathogen, predisposing agent and vector of plant viruses. Plant parasitic nematodes are known to interfere the activity of beneficial nitrogen fixing Rhizobium bacteria in leguminous crops.
In this review, only economically important plant parasitic nematode problems of crops in India and their management options are briefly discussed:
1. Root knot nematodes (Meloidogyne spp.)
Root-knot nematodes (Meloidogyne spp.) are global menace to crop production (Sasser, 1980). It has a very wide distribution and causes serious damage to crops particularly in vegetables. The average yield losses in the world are believed to be about 5% and could be more in the developing countries of tropic and sub-tropic (Taylor & Sasser, 1978). Considering the universal significance of root-knot nematodes, an International Meloidogyne Project (IMP) was operated (1975-1984) with its head quarter at North Carolina State University, USA and its collaborating centres were in many developing countries of the tropics and subtropics. Worldwide more than 97 known species of root-knot nematode have been recorded and only 14 known species of Meloidogyne are recorded in India. Four species of root knot nematodes viz. Meloidogyne indica, M. lucknowica, M. triticooryzae and M. piperi have been described from India. Various insect-pests, diseases and weeds are inflicting damages to vegetable crops. Root-knot nematodes (Meloidogyne spp.) are one of the potential constraints for cultivation of vegetables particularly in the developing countries of tropics and subtropics. Vegetable crops harbour large number of plant parasitic nematodes but root-knot nematode is most damaging one. It affects the crop directly and indirectly by interaction with various soil borne fungi, bacteria and viruses. The most predominant species of root-knot nematodes are Meloidogyne incognita, M. javanica, M. arenaria and M. hapla. All the species of root-knot nematodes produce a characteristic ‘root gall ’or‘knotted root symptom, which could be easily recognized by naked eye. There is hardly any vegetable crop which is not attacked by the root-knot nematodes. Therefore, it has widely been 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 hindrance 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.
The infection of root-knot nematode produces characteristic disease symptoms on the below ground root system popularly known as ‘root gall’ or ‘knotted roots’. Different sizes of galls are induced depending on their host and the species of the nematode involved. On cucurbits, the nematode induces large galls, whereas in chilli small size of galls is produced. Usually the infection of M. hapla produces small galls as compared to M. incognita and M. javanica. 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 develops. 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. The interaction of root-knot nematodes is known in many vegetables, fibre, pulses and plantation crops. However, the most common problem is the breakdown of disease resistance and wilting of healthy plants. The most common interaction of root knot nematode with Ralstonia (=Pseudomonas) solanacearum is causing “Pseudomonas wilt” in tomato, brinjal and potato.
Nematode management options
Root-knot nematodes are polyphagous in nature, having high reproductive potential, and have acquired unique mechanism of survival strategy through laying their eggs in protective gelatinous matrix. Management of root-knot nematode is not easy task under intensive crop cultivation system. Therefore, the idea of keeping the nematode population below the economic damage level by adopting different available tactics is advised to the growers. The young tender seedlings of various crops are very much vulnerable to attack by nematode while the older plants achieve some degree of tolerance. Considering the farmer’s suitability, following hygienic cultivation practices of vegetable crops could be suggested for managing root-knot nematodes:
Cultural practicesCultural practices are the most effective and economical means of managing insect-pests and disease including nematode problems.
• Two to three summer ploughings (20 cm deep) during the months of May – June at the interval of 15 days expose nematodes, weeds, disease propagules and hibernating stages of insect-pests before the sun and cause their death.
• Inter-cropping with antagonistic plants like marigold (Tagetes spp.) reduces soil population of many soil nematodes including root-knot nematodes. Incorporation of such crop in cropping system either as inter-crop or alternative crop should be considered whenever feasible.
• Crop rotation with resistant varieties or non-host crops like mustard, sesame, maize, wheat etc. are useful to bring down the soil population of nematodes below the damage threshold level.
• Application of organic manure, Farm Yard Manures (FYM) at 18 to 20 t/ha reduces nematode population through their action of released toxic substances, enhanced crop tolerance and encouraging soil microbial antagonists
Resistant varieties
Plant resistance plays an important role in integrated management of root-knot nematodes diseases, however, availability of resistant varieties of vegetable crops are very few in number and many of them are not acceptable to the farmers for their suitability.
Some of the resistance varieties exhibited resistance or tolerance reaction to root-knot nematodes are as given below:
Tomato: SL-120, Hisar Lalit, PNR-7, Hisar N-1, Hisar N-2, Hisar N-3, NT-3, NT-8 NT-12, Ronita, Patriot, PAU-5, Mangla and Karnataka Hybrids.
Chilli: Pusa Jawala, CAP-63, CA-2057, Sindhuri, NP-46 A, Mohini, SP-26, P-6-3, K-235
Brinjal: Giant of Banaras, Black beauty, Gola, Gachha Baigan, Pbr-91-2, IC-95-13, HOE-101, Red Wonder.
Cowpea: Barasati mutant, 82-IB, C-152, IHR-29-5, GAU-1
Pea: B-58, C-50
Potato : Kufri Dewa
Okra: Kanki local green, Harichickni,Vaishali Badher
Pumpkin: Dasna, Jaipuri
Water melon: Shahjanpuri
Ridge gourd: Panipati, Meerut special(modified after Anon. 1988)
Chemical control
Chemical control with the application of nematicides is the most effective means of nematode management. However, most of the effective nematicides have been withdrawn from the world market. At present, a few insecticides having nematicidal property are available to the farmers but because of their high doses required to manage nematode, it becomes cost- ineffective and leaves high pesticide residues to the harvested crops. Despite their inherent drawbacks, chemical nematicides could be applied judiciously so that the doses and cost are reduced drastically. The application of nematicides through bare-root dip treatment, seed treatment and nursery bed treatment has been proved to be effective to protect the young seedlings from nematode attack.
Nursery bed treatmentIn most of the cases, the infection is carried through infested seedlings from nursery bed. The damage caused by root-knot nematode to the root system of tender seedlings is more harmful than to older plants. The application of nematicides to nursery bed helps to raise nematode free seedlings. Moreover, it reduces the dose of nematicides and cost substantially. The soil application of carbofuran (Furadan 3G) at 0.3 gm a.i./m2 is sufficient for producing nematode free seedlings of many transplanted vegetables crops. The treatment of nursery bed with sebuphos (Rugby 20 WP) or carbofuran (Furadan 3G) or benfurocarb (Oncol 50 WP) at 0.3 or 0.6 g a.i./m2 at the time of sowing reduced root-knot nematode and in seed yield of tomato by 25-62%.
Bare-root dip treatmentThe seedlings of many transplanted vegetables crops can be dipped in systemic nematicides like oxamyl, prophos, and dimethoate at 500 to 1000 ppm for six hours to denematize the roots. These practices will further ensure to protect the root system of tender seedlings from early attack of nematodes. The seedlings of transplanted vegetables like brinjal, tomato, chilli and planting materials of pointed gourd treated with carbosulfan (Marshal 25 EC) at 500 ppm for six hours provided effective control against root-knot nematodes. Nursery bed treatment with carbofuran at 0.3g a.i./m2 coupled with seedlings deep with carbosulfan 25 EC at 500pm before transplanting effectively manage M. incognita and enhance crop yield in vegetables.
Bare root dip treatment of tomato and brinjal seedlings with Zolone (Phosalone 35 EC) or monocrotophos (Monocil 36 SL) or carbosulfan (Marshal 25 ST or DS) at 0.05% reduces root-knot nematode and increase the yield.
Seed treatment
The practice of seed-soaking and seed-dressing are important prophylactic measures which give adequate initial protection to the young seedlings of tomato, brinjal, okra, chilli, etc. The most commonly used systemic nematicides viz. fenamiphos, isofenphos, carbosulfan etc. are used at 2-3% w/w.
Seed dressing with carbosulfan (Marshal 25 ST) at 3% w/w is quite effective for managing root knot nematode in okra, bottle gourd, pointed gourd, bitter gourd and jute. Seed soaking with dimethoate, carbosulfan (Marshal 25 EC) can also be adopted for providing better crop with early protection against nematode.
Field application
Field application of carbofuran 3G at 2Kg a.i./ha in tomato, brinjal and okra reduces nematode population and increases yields.
Biological control
Despite its several limitations, biological control of root knot nematode is cost effective and eco-friendly method. As a component of integrated nematode management, biological suppression of root-knot nematode is well documented. Several bioagents have been exploited against this but so far only three bioagents viz. Paecilomyces lilacinus (Khan & Goswami, 2002), Psuedomonas fluorescens and Pasteuria penetrans have widely been recognized as effective and promising bioagents. Some formulations of P. lilacinus (Bionematon, Yorker) and Pasteuria penetrans (Pasutsuria 50 WP), Trichoderma viride and T. harzianum(Trichostar, Tricho guard, Bioderma, Ecoderma etc) are available in the market for checking root knot nematodes.
Integrated Approach for root-knot nematode managementIndividual method of nematode control has either proved ineffective or uneconomical approach against root knot nematodes. Therefore integration of various suitable tactics may be an ecofriendly, economically viable and practically feasible approach for managing nematode problems in crops. The adoption of deep summer ploughing during summer period at fortnightly interval along with organic matter application followed by planting with nematode free seedlings is a feasible approach to reduce nematode population. Similarly, farmers with their available resources could follow integration of cultural, biological, chemical methods and resistant varieties in suitable combination for each crop cultivation system. Soil solarization/summer ploughing alone as well as in combination with carbofuran 3 G at 2 Kg a.i./ha has been found effective against nematodes infesting brinjal, chilli and tomato. Seedlings raised in solarized nursery beds treated with carbofuran at 0.3g a.i/m2 integrated with application of neem cake at 5q/ha gives better check against nematodes infesting vegetables and increases yield.
2. Wheat seed gall nematode (Anguina tritici)
This nematode is one of the most serious pests of wheat in the country. It is the oldest known plant parasitic nematode and the nematode alone causes ‘ear cockle’ disease in wheat and in association with the bacterium, Clavibactor tritici produces ‘yellow ear rot’ or ‘tundu’ disease. The host range of this nematode is very few in number and wheat is considered as the most suitable host. Although the control of this nematode is simple and easy as compared to other plant parasitic nematodes, it is still troublesome in many wheat growing parts of Rajasthan, UP, Bihar and Madhya Pradesh particularly in tribal belts where tons of wheat grains are wasted every year (Anon, 1995-2001). Wheat galls are the primary source of dissemination for nematode either as seed mixture of cockle. The juveniles of A. tritici remain viable in anhydrobiotic state inside the cockle for several years. After sowing the galls/cockles come in contact with soil moisture and become soft leading to release of large number of second stage juveniles. These juveniles infect the growing point of seedlings as ectoparasite and are carried to inflorescence due to the natural growth of seedling. The nematode enters the floral primordia and become endoparasite and eventually the floral primordial converted into seed galls.
The initial visible symptom is enlargement of basal stems near the soil surface at the stage of 20 to 25 day-old seedlings. Generally the infested plant exhibits more number of tillers and grows fast as compared to healthy ones. Twisting, curling, crinkling of leaves and stunted growth are common symptoms in the early stage of plants growth the affected ears are typically swollen, broader with or a few awns on the glumes. The cockled ears contain initially green galls later in each spike-let 1 to 5 galls can be seen.
Yellow ear rot or tundu disease
The early stage of plant exhibits similar disease symptoms as that of ear cockle disease. The yellow ear rot disease is primarily caused by a bacterium, Clavibactor tritici only in the presence of nematode, A. tritici. Under humid climatic conditions, the characteristic symptoms are appeared with a production of bright yellowish bacterial slime on the leaf surface which can be seen trickling down the ears. During dry weather, these slimes become hard, diseased spikes are generally distorted, stunted and narrower than healthy ones with the grains partially or completely converted by bacterial mass.
Management options
The nematode is easy to manage as because the gall is the only source of ear-cockle and tundu disease. Both physical and mechanical methods are successful for eradicating this nematode from several developed countries of the world, however, in India this nematode is still becoming problems probably due to poor awareness and failure of national campaign against the dreadful disease of wheat.
Physical methods
• Hot water treatment of wheat seed-lots at 54 to 56 0 C for 10 to 20 minutes.
• Water floatation of seed galls in 5-10% salt solution for 5 to 15 minutes. Seeds containing nematode gall will float in water surface and can be collected and discarded.
Mechanical methods
Fanning or winnowing is an effective method to remove the galls from seed lots. Sieving/ screening is a common practice and most successful method for eradication of seed gall nematode from many countries, though complete removal of gall is not possible with this methods because some large sized galls are retained on the sieves.
3. Cereal cyst nematode (Heterodera avenae)
Heterodera avenae is the causal organism of a serious disease popularly known as ‘molya’ disease of wheat and barley. This disease was first time recorded from Rajasthan in India and subsequently it is known to occur in major wheat growing states viz. Punjab, Haryana, Uttar Pradesh, Delhi, Himachal Pradesh and Madhya Pradesh of India (Kaushal et al., 2001).The nematode is mainly confined to the family gramminae.
The nematode infested fields exhibit patchy growth with stunted and yellowish plant. Infested plants shows thin narrow leaves, reduced tillering, fewer leaves and small size of ear heads with reduced number of grains. The roots of nematode attacked plants appear bushy, bunchy due to emergence of root lets at the site of infection and slight swelling of root tips may be encountered. The above ground symptoms are often confused with the general deficiency symptoms. However, presence of cysts is the only confirmatory evidence for nematode infection.
The second stage juveniles infect the growing tips of roots and upon feeding develop specialized syncytial cells for their growth and development. After three months, the juveniles achieve lemon-shaped sedentary female which is found to attack with roots. Eggs are laid inside the female body and after death of female, the body cuticle transform into brown cyst. During off-season, nematode survives in cysts.
Management options
Cultural practices
• Crop rotation with non-hosts like sarson, toria, raya, taramira, gram, berseem, carrot, coriander etc. with wheat.
• Deep summer ploughing (2-3) at an interval of 10-15 days during hot summer months
• Growing wheat cultivar C-306 as trap crop early in October
• Growing Resistant varieties: Barley cultivar like Rajkiran, C-164, BH-72.
Chemical control
Field application of Carbofuran (FRADAN 3G) at 2kg a.i./ha have been found effective (Kaushal et al., 2001).
Integrated management
Integration of different tactics was found economical against cereal cyst nematode. Early sowing in the month of November along with field application of carbofuran at 2kga.i./ha is quite effective in increasing yield and reduction of cyst population in soil.
4. Potato cyst nematode (Globodera rostochiensis, G. pallida)
It is one of the serious nematode pests of potato in some southern states like Tamil Nadu, Karnataka, and Kerala. The nematode is popularly known as ‘golden nematode’ and has been recognized as one of the major crop protection problems of the world. The nematodes are responsible for average losses of 9% of global potato amounting to about 40 million tons (Krishna Prasad, 1995). In India, potato cyst nematode is known since 1961 when F.G. Jones detected this nematode from a field at Vijayanagaram state farm in Ootacmund of Nilgiri Hills in Tamil Nadu. Considering importance of potato cyst nematode in the country, the Government of Tamil Nadu imposed the Destructive Insect Pest Act 1919(DIP Act 1919) in 1971 to contain the nematode in the Nilgiri Hills.
It is difficult to detect the disease symptoms at low infestation of nematode but the symptoms are prominent only after the build up of population in soil. The disease symptoms appears in small patches of poorly growing plants, temporary wilt of plants in day time, stunted plants, unhealthy yellowish foliage and poor root systems, reduction of number and size of tubers and production of potato yield gradually reduced over the years. The nematode is primarily confined to the family solanaceae and depends on the host root diffusates which induce the hatching of second stage juveniles from eggs. The second stage juveniles infect the root and modify the cells as giant cell for ensuring permanent nourishment to reach adult stage. The adult females are white spherical shape which is found attached with root and after death of female turn into brown cyst. All the eggs laid by the females are retained inside the body. This cyst containing eggs are protected and remain viable for several years in soil even in the absence of potato. The pathotypes RO1 and RO5 of G. rostochiensis and Pa2 and Pa3 of G. pallida of potato cyst nematodes are known to be prevalent in India.
The nematode cyst containing eggs are generally spread through soil particles adhering to tubers, farm implements, gunny bags, farmers’ feet etc. However, irrigation water or rain water running down the hill slope carry the cyst from the infested field to uninfested fields.
Management options
Cultural practices
• Growing non-host solanaceous vegetable crops like cabbage, cauliflower, beet root, carrots, garlic, radish, turnip etc. One of the most useful rotation as potato-cabbage-carrot is commonly practised by the farmers of Nilgiri Hills.
• Resistant Varieties : Kufri Swarna
Chemical control:
Use of carbofuran (FURDAN 3G) at 2kga.i./ha is effective to reduce nematode population as well as increasing potato yield.
Key nematode pests of rice in India
i) Rice root knot nematode, Meloidogyne graminicola
ii) Rice root nematode, Hirschmanniella spp.
iii) Rice stem nematode, Ditylenchus angustus
iv) White tip nematode, Aphelenchoides besseyi
v) Rice cyst nematode, Heterodera oryzicola
5. Rice root knot nematode (Meloidogyne graminicola)
Rice root knot nematode, Meloidogyne graminicola is a well established nematode pest of rainfed upland rice. It poses serious problems in boro and kahrif nursery particularly in sandy loam or recent alluvial soils of West Bengal. It is also becoming problem in transplanted rice grown in waterlogged conditions. The widespread occurrence of M. graminicola has been found in Assam, West Bengal, Gujarat, Orissa, Karnataka and Tripura.
The above ground symptoms are nonspecific 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 root lets and root hairs. The yield losses due to M. graminicola has been estimated to be between 16 to 32 % in upland rice and in severe cases go up to 64 %( Phukan, 1995). A complete failure of boro rice nursery in ‘simurali’ in the district of Nadia, West Bengal has been noticed (Anon, 2001)
After harvesting of rice, the nematode may survive in egg stage in soil or continue to reproduce on various weeds. Female often remains concealed within root tissue and eggs are laid in cortical tissues and hatched juveniles reinfect the same roots. It completes life cycle within 19 days at 22 to 29 0C in upland rice.
Management options:
Cultural practices
i.Scheduling crop rotation with non-host crops as cauliflowers, sesame, groundnut, onion, maize, soybean, cowpea
ii. Weeding: Rice fields supports a diverse kind of weeds like Echinochloa spp., Eleucine indica, Paspalam scrobiculatum, Cyperus spp. etc.
iii. Resistant varieties: CR-143-2-2, CR-147-2-1, CR-1009, CT-428, Sudha, Murti
Chemical approachesi. Seed soaking with carbosulfan (Marshal 25 EC) at500ppm or Carbosulfone at 0.1% for 12hrs
ii.Bare dipping in carbosulfan (Marshal 25 EC) at 500ppm for 20 minutes
iii. Nursery bed treatment with carbofuran (Furadan 3G) at 1kga.i./ha and similar dose of nematicides at 7 and 50 days after transplanting
6. Rice root nematode (Hirschmanniella spp.)
Rice root nematode is a migratory endoparasite of roots and occurs predominantly in moist habitat. Rice root nematode, Hirschmanniella spp. are unique migratory endoparasites of rice and cause yield losses to the extent of 19% in rice in West Bengal (Ahmad et al., 1984). Hirschmanniella oryzae and H. mucronata are two economically species in rice and occurrence of H. gracilis is doubtful in India (per. Comm. Dr. M. R. Siddiqi). The juveniles 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. Its feeding sometimes extends to central vascular regions. The infected roots exhibit water-soaked brown lesion which are of mostly spindle shaped. The physiological function of infected plants is disrupted and plants growth reduced. The above ground symptoms are non-specific as stunted growth, leaf chlorosis, reduced tillering and delayed flowering.
The population of Hirschmanniella species was found maximum during active growth phages of rice. The population build up of this nematode increases after transplanting up to 80 days of rice(Singh & Jain,1995) and declines when roots of rice starts degenerating.
Rice root nematode survives better in poorly drained clay and heavy soils. It can survive even in high temperature of May-June (35-45 0 C) as well as low temperature of December-January (8-12 0 C) in the North Indian conditions (Mathur & Prasad, 1973). Their survival in soil is much longer than in roots in flooded soils. H. oryzae can survive more than 12 months in wet soils. A number of weeds found in rice fields serve as alternative host for this nematode. In West Bengal, the nematode can survive in the months of summer in the absence of any crops under laterite soil conditions (Khan & Mukhopadhyay, 2002). Under rice-wheat cropping system, the nematode maintains a very high population, though wheat is not the host for the nematode. Spread of this nematode occurs mainly through irrigation water, flood water, soil adhering to farm implements, field workers and root of rice seedlings.
Management options
Direct seeding of rice has been found to be more vulnerable to attack by this nematode compared to transplanted crop (Singh & Jain, 1995).
Cultural practices
i. Early planting of rice in the month of June or middle of July
ii.Use of organic amendments such as mustard cake or neem cake at 220-240 kg/ ha
iii. Balanced NPK fertilization
iv. Crop rotation with wheat, linseed, potato, cauliflower, mustard and gram in rabi season
v. Deep dry summer ploughings
vi.Weeding during standing rice and in absence of the crop
vii. Growing resistant varieties/cultivars: TKM-9, CR-142-3-2, CR-52, N-136, W-136
viii. Sesbania rostrata can be used as trap crop for H. oryzae
Chemical approachesi. Nursery bed treatment with carbofuran 3G or phorate 10 G at1.0 kg a.i. /ha followed by I.0 kg/ ha at 7 and 50 days after transplanting
ii. Bare root dip treatment with chlorpyriphos/ carbosulfan 25 EC / monocrotophos 36 EC at 1000-2000ppm for 20 to 30 minutes
iii. Seed soaking with carbosulfan 25 EC or isofenphos at 0.2% for 6 hours.
7. Rice stem nematode (Ditylenchus angustus)
Rice stem nematode is usually problematic in rice grown in deep water situations. The vernacular name ‘stem nematode’ is derived from the stem inhabiting nature of the nematode. It is an obligate parasite and serious pest of rice causing popular disease symptom referred to as ‘Ufra disease’. In Bangladesh and some areas of India, 100 % yield loss has been recorded due to severe attack of D. angustus. The nematode has been found prevalent in Malda, Murshidabad, Hooghly, 24-Parganas, Jalpaiguri, Coochbehar and West Dinajpur districts of West Bengal and Sibsagar, Jorhat, Morrigaon, Sonitpur, Borbeta and Dhubri in Assam (Phukan, 1995)
The symptom produced by rice stem nematode is popularly known as Ufra or dakpora disease. The Ufra symptoms appear in patches and subsequently spread to the entire field. The nematode attack at vegetative stage results in yellowing or whitish pattern on the leaf sheath and margin becomes corrugated. In due course of time, the splash pattern turns brownish stains and stem and inter node become black. Twisting of leaf and leaf sheath are commonly found symptoms. Sometimes infested nodes give bushy appearance due to branching. The Ufra symptoms may be grouped as:
Swollen or Thor Ufra: Panicle does not come out, it remains enclosed within the leaf sheath and infected portion tending to branch.
Pucca or Ripe Ufra : Panicle emerges partially and panicle bears filled grains at tip only.
The primary sources of infection D. angustus are rice stubbles, straw, wild rice and weeds found in rice fields. The nematode can overwinter through quiescent state (fourth stage juvenile) which remains viable up to 15 months. They live in coiled anhydrobiotic state in grains (Prasad & Varaprasad, 2001); dried plants parts left in the fields and reinfect the crop in the next season.
Management options:
Cultural approaches
i. Destruction of rice stubbles, weeds and wild rice in the rice fields
ii. Crop rotation with jute, sesame, mustard with rice
iii.Summer ploughing helps nematode to destroy by desiccation in the scorching heat of sun
iv. Growing early (Padmapani) or resistant (Rayada selection) varieties (Prasad et al., 2001)
Chemical approaches
i. Spraying with diazinon at 0.01%
ii. Soil application of carbofuran 3G or phorate 10G at 1 kg a.i. /ha at transplanting
8. White tip nematodes (Aphelenchoides besseyi)
A. besseyi is a specialized parasite attacking aerial parts of its natural host, rice. Though rice is the most suitable host of this nematode, it can infect tuberose, onion, soybean, sugarcane, oat, millets, orchids etc. The most characteristic disease symptom is ‘white tip’ in rice leaf produced by this nematode due to which the common name of the nematode is ‘white tip nematode’. It has been recorded in serious form in rice from Gujarat, Tamil Nadu, Madhya Pradesh, Andhra Pradesh and West Bengal. In West Bengal, the nematode is becoming problem in the rice fields adjacent to tuberose fields in different tuberose growing areas of state (Khan, 2001). The nematode is prevalent through out the state of West Bengal (Das & Khan, 2007).
It is easy to detect the presence of nematode within the rice seeds. In field, the initial appearance of symptoms as the leaf tip up to 5cm becomes pale yellow or whitish at tillering stage and subsequently 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.
A. besseyi survives as pre-adults as well as in adult stages (quiescent state) beneath the hull of rice kernel and does not survive in soil after harvesting rice plants. Infected seeds or presence of other alternative hosts help nematode to survive up to next crop. They usually remain in coiled anhydrobiotic state in rice between lemma and palea up to 3 years. The infected rice seed is the only means for rapid spread of A. besseyi. It also spread through irrigation water or flood water. Female lays eggs on rice plants. All the developmental stages occur on rice plant. The life cycle of A. besseyi is completed within two weeks and, therefore, several generations are completed within a cropping season.
Management optionsProphylactic measuresi.Healthy rice seed checks the spread of white tip disease of rice
ii. Rice stubbles to be burnt or destroyed after harvesting
iii. Simple spreading the rice seed on the concrete floor on bright sunny days at least 4 hours for 6 consecutive days kills nematodes inside the grain
iv.Seed-soaking in water(1:2 ratio) for overnight followed by adding two volume of boiling water for 10 minutes and then drying of seeds in shade
v.Seed treatment with carbosulfan 25EC at 0.1% for 12 hours.
9. Rice cyst nematode (Heterodera oryzicola)
Heterodera oryzicola has been reported as a serious pest of rice in Kerala. It has also been known to occur in Burdwan and Bankura district of West Bengal (Rao, 1985). This nematode is one of the serious pests of rice and banana in Kerala (Kuriyan, 1995). Its occurrence has been recorded from Karnataka and Goa (Prasad, 2002).
The browning of roots and chlorosis of leaves, retardation in growth, early flowering of plants by 10 to 15 days and partial filling of grains are the typical symptoms of infection of H. oryzicola. No gall developed on rice roots. The presence of brown cyst on rice root is the confirmatory evidence of this nematode infestation. One life cycle is completed in 30 days and 12 generations may occur in a year. Yield losses could be to the extent of 38% due to the attack of nematode (Rao, 1978). The nematode spread through infested seedlings, irrigation water or farm implements.
Management options
i. Soaking of seeds with phenamiphos at 0.02% for 6 hours
ii. Soil application of carbofuran or phorate 1kg a.i. /ha at 7 and 50 DAT
iii. Growing resistant varieties like Lalnakanda, CR143-2-2
iv.Regulatory measures on the movement of banana rhizomes as well as rice seedlings from infested areas have to be adopted.
10. Burring nematode (Radopholus similis)
This nematode is internationally quarantined pest and is capable of parasitizing many fruits, spices and plantation crops. It is known to cause a serious disease of black pepper popularly referred to as ‘pepper yellows’ in Indonesia and ‘slow wilt’ in India and ‘spreading decline’ in Florida. Many economically important crops like banana, citrus, betelvine, coconut, arecanut black pepper, ginger etc. are seriously affected by the nematode. The nematode is mainly problem in Southern states like Kerala, Karnataka, Andhra Pradesh (Parvatha Reddy & Singh,1980). Recently, it has got spread to the state like Orissa, Manipur, Maharastra, Madhya Pradesh and Himachal Pradesh and Gujarat possibly through indiscriminate movement of planting materials of banana, ginger and turmeric rhizomes.
Nematode infested banana plants exhibits ‘toppling disease’ at bearing stage, premature defoliation, poor plant vigour and finally reduction of bunch size and weight. In root, lesion develops on root and subsequent rotting and decaying of tender roots due to the involvement of other soil microorganisms. The coconut plants attacked by R. similis show general decline symptoms like yellowing, stunting and smalling of leaves and button shedding resulted in low yield. In black pepper, slow growth of vines, yellowing of leaves, rapid panicle declines followed by severe die-back and death of vines are common symptoms. The roots of coffee, arecanut, betelvine are seriously attacked and develop characteristic lesions and root decay and rotting. The nematode is a migratory endoparasite of root and feed on the succulent tissues of feeder roots. Due to their intracellular movement, the nematode destroys the cells and forms burrows or cavity inside the root. All the developmental stages are capable of feeding roots. Eggs are laid in root tissues and newly hatched juveniles start feeding and develop inside roots. Therefore, the entire life cycle may be completed within the roots. The total life cycle is completed in 20-25 days. In India, only the banana race of R. similis is prevalent.
Management options
The nematode is difficult to manage due to its endoparasitic nature and wide host range.
Preventive measures
• Planting material/seedlings should be free from nematode
• Any occurrence of discolouration on the rhizome should be removed and treated with Bordeaux mixture or nematicides
• Hot water treatment of rhizomes at 50-55 0C for 20-25 minutes could be done to denematize the planting materials.
• Raising of seedlings of coconut, arecanut, black pepper from nematode free nursery bed
• Before planting, sun drying of banana rhizomes is also effective to reduce nematode population
Curative measures
• Application of carbofuran 6 g a.i. or phorate 3 g a.i./plant 2-3 times in a year is effective to reduce the nematode in coconut and banana.
• Application of neem cake at 400 g/plant once at planting and second dose after 4 months increase bunch weight and the yield of banana
• Avoiding susceptible crops as intercrop
• Intercropping with Crotalaria juncea reduces R. similis population
• Bioagents like P. lilacinus, Glomus fasciculatum, Pasteuria penetrans are promising agents against R. similis
Resistant / Tolerant Varieties:
Banana : Kadali, Pedalimoongil, Kunnan, Pey Kunnan, Pisang Seriby
Arecanut : Resistant: VTL-11x VTL-17( Sundarraju & Koshy, 1988)
Tolerant: Indonesia-6 (VTL-11)
Mahuva-B, Andaman-5 (VTL-29e)
Coconut: Kenthali, Klappawangi, Hybrid Java Giant (JG X Kulasekheram Dwarf Yellow (KDY), KDY X JG, Java Tall X Malayan Yellow dwarf, San ramon X Gangabondan (Sosamma et al.1980)
11. Citrus nematode (Tylenchulus semipenetrans):
Citrus nematode is found in all the citrus growing areas of the country and is widely recognized as economically important pest of citrus. It is one of the causal factors for ‘slow decline’ in citrus’ which is characterized by general reduction of the 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 nematode is best confirmed by microscopic observations of soil and root samples. The female nematodes and their gelatinous matrix containing eggs adhering soil particles and 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 to 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 nematode and to the degree of infection.
T. semipenetrans feeds on surface layers of roots causing discolouration and necrosis. A young female penetrate deeper root tissues and establishes a feeding site around the head. The feeding site comprising of 16 cortical cells referred to as ‘nurse cell’. The posterior part of mature female body remains outside and eggs are laid in a gelatinous matrix outside the host tissue. The life cycle of this nematode is completed within 6-8 weeks under optimum temperature at 25 to 31 0C.
Management options:
Prophylactic measures
a. Nursery raising of seedling should be free from nematode infection
b. Previously infested citrus orchard should be either avoided or fumigated to kill any nematode population in soil.
c. Preventing run off water from adjacent infested citrus orchard
d. Use of clean equipment/implements for cultural practices because movement of any adhering soil particles from one place to another in orchard may disseminate the nematode.
It is difficult to eliminate the nematode once it is established in orchard. Therefore, regular monitoring is essential for preventing the nematode to reach above the damage threshold level. Usually the nematode at low population level (500/g of feeding root) are not damaging to the crop but at high population (4000/g root) causes devastating damage to citrus plant (Nickle, 1991).
Curative measuresa. Application of oilcakes of neem, mahua, groundnut etc. at 1kg/plant can reduce nematode populations.
b. Combined use of neem cake at 1kg /plant along with carbofuran 3G (Furadan) 1.0 kg a.i./ha is also effective.
c. Use of biocontrol agent like Paecilomyces lilacinus at 4 g /plant along with carbofuran 3G (Furadan) 1 kg a.i./ha gives good results (Parvatha Reddy et al., 1996).
d. Use of resistant ‘trifoliate’ citrus stock may be an efficient method to check the nematode.
Cultural practicesRemoval of old feeder roots before the start of growth flush followed by application of FYM helps to reduce nematode population in soil.
12. Foliar nematode (Aphelenchoides besseyi) of tuberose
Tuberose is commercially important for loose flower, cut flower and for extraction of essential oils. Its commercial cultivation in West Bengal was started in the second half of 19th century to meet aesthetic need of the English people harboured in Calcutta. At present the total area under tuberose in India is estimated to be about 20,000 ha, out of which 2,110ha is in West Bengal and it is mainly confined in Kolaghat-Panskura, Ranaghat and Haringhata areas. In terms of area and production of tuberose, West Bengal ranked first. Recently, foliar nematode, Aphelenchoides besseyi has been appeared as a serious problem in tuberose in West Bengal. This nematode was first time reported from Hawaii Islands on the leaves of tuberose (Holtzman, 1968). The occurrence of floral malady caused by A. besseyi in tuberose was recorded from Ranaghat areas of Nadia district of West Bengal (Chakraborti & Ghosh, 1993). In India, this nematode is widespread in Eastern and Southern states particularly in rice causing ‘white tip disease’ and estimated to cause yield loss 20 to 30%in rice, though floral disease caused by A. besseyi in tuberose was not encountered any other states except West Bengal. Recently, it has got spread to neighbouring state, Orissa either through movement of bulbs or other means. Recent survey results revealed that A. besseyi is a major limiting factor for cultivation of tuberose in Ranaghat and Haringhata regions of Nadia, Bangaon of 24-Parganas (South) and some pockets of Howrah and Midnapore districts of West Bengal. The high population of A. besseyi was also recorded from fields of Kolaghat-Panskura-II of Midnapore district. The ‘single’ cultivar of tuberose was found to be the most vulnerable to damage caused by A. besseyi as compared to ‘double’ cultivar. Khan et al. (1999, 2001) investigated for severe foliar disease infestation in tuberose and found A. besseyi is the primary causal agent for malformed flowers. The population of A. besseyi causing white tip disease in rice is the same population infecting tuberose and causing floral disease (Khan, 2001). A. besseyi is now recognized as the key nematode pest of tuberose and it was becoming a potential threat for cultivation of tuberose in West Bengal.
The infected flower stalk initially appears rough, stalk become crinkled, stunted and finally distorted and in severe cases flower buds failed 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 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 & Pal, 2001). The ovary contains large number of nematodes. This nematode is more serious during rainy season generally from July to September and cent percent loss of second year crop particularly in ‘Calcutta single’ cultivar of tuberose was recorded. However, in ‘Calcutta double’ cultivar 30% to 40% flower stalk rendered unsaleable and from individual flower stalk up to 45,000 nematodes were recovered (Khan et al., 2002). In Calcutta single, the nematode could cause 38 to 59% yield loss (Pathak & Khan,2005)
The dissemination of A. besseyi occurs through bulbs collected from infested fields. The nematode survives in coiled anhydrobiotic condition (quiescent pre-adult and adult stages) in the scaly leaves outside the bulbs. The nematode can also survive in the dried scaly leaves, stems and flowers more than 25 months; however, they can not survive in soil for long time (Khan, 2004).
Nematode Management a. The planting material (bulbs) should be soaked in neem-seed-kernel-extract (home preparation from locally available neem) for overnight or dipping of bulbs in monocrotophos 36SL at 500ppm for 6 hours.
b. After sprouting of the bulb, three to four sprayings with monocrotophos 36 SL at500ppm at 15 to 20 days interval should be given (Khan et al. 2005).
c. In the second and third year crop, sprayings with monocrotophos 36 SL at 500ppm at 15 to 20 days interval starting from the month of May onward reduce the nematode infestation.
d. Clean cultivation of tuberose and any infested parts of plants found in the field should be burnt immediately (Khan, 2006).
13. Reniform nematode (Rotylenchulus reniformis):
The adult female of reniform nematode (Rotylenchulus reniformis) is an obligate, sedentary semi-endoparasite of a wide range of food, fibre, oilseed, oilseed, fruits and plantation crops. The common name ‘reniform’ was derived from the kidney-shaped mature female. It has worldwide distribution and is receiving importance as national pest of crops. At present, there are 10 species of reniform nematode known worldwide but R. reniformis is the most widespread and has economic importance. In West Bengal, R. reniformis has been known to be associated with many vegetable crops, banana, tuberose, tea, pulses, fruits, betelvine etc.
The 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 formation of necrosis on 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 diseases complexes. It has also been reported to parasitize the bacterial nodules.
The nematode is capable of surviving in air dried soil for a long period of time (Gaur & Perry, 1991). The retention of moulted cuticles of previous stages is a unique adaptation for survival of nematode in soil. Individual young females, males and fourth stages juveniles could survive in a coiled anhydrobiotic state with encrusted cuticles in soil. Survival of this nematode inversely related to the rate of moisture loss in soil. Therefore, alternate drying and wetting of soil resulted in sharpe decline of population density of the nematode in soil.
The first moult occurs within eggs and eggs are hatched in water without the influence of root exudates. Juveniles develop to pre-adult stage without any feeding host tissue and quickly completing three superimposed moulting. The young female is the only infective stage. After infection to the roots, young female orient themselves perpendicularly to the longitudinal axis of roots with the posterior part remain outside the root. After establishing the feeding site, it develops into kidney shaped female with posterior portion protrude outside the root. Egg laying starts within 7-10 days after invasion and eggs are laid into a gelatinous matrix secreted by six specialized cells around vagina. Each egg mass contains 30-200 eggs. Total life cycle is completed within 3 to 4 weeks depending upon temperature and host suitability.
Management options:
Cultural methods:Crop rotation with non hosts crops like mustard, maize, sugarcane, marigold
Growing the susceptible crops in winter seasons in the multiple cropping systems
Organic managements
Application of FYM, oilcakes like neem, karanj, mustard etc. have been found promising.
Summer ploughing:Two to three summer ploughings during hot months
Irrigation management:Irrigation between ploughings results in alternate drying and wetting which may stimulate exsheathment of young female of R. reniformis
Crop husbandry:
Good crop cultivation practices like field preparation, fertilizer application and moisture management can improve crop tolerance to nematodes
Resistant Varieties :
Cowpea: Pusa phalguni, C-152, RC-48
Papaya: Solo, Washington, Coorg Honey Dew
Onion: Evergreen
Chickpea: BG-425, BG-426, BG-434, BG-268, BG-273
Blackgram: UG-201, UG-135
Chilli: Pusa Jawala
Chemical Control:
Soil application of carbofuran (Furadan 3G) at 2 kg a. i./ha gives good control but it may not often be economical in many low value crops. However, judicious use of nematicides may be adopted by restricting their use at nursery bed, seed treatments, bare dipping of vine cuttings and pit application particularly for transplanted crops.
14. Lesion nematodes (Pratylenchus spp.)
Pratylenchus spp. are migratory endoparasite of root. The vernacular name of ‘root lesion nematode’ is derived from the discoloured patches (lesion) develop on roots. It has a very wide host range including important crops like wheat, maize, cotton, potato, rice, banana, tea, vegetables, ornamentals and fruits. Some nematode species like Pratylenchus thornei in wheat, soybean, chickpea, sunflower and opium, P. zeae in maize, P. indicus in rice, P. loosi in tea, P. coffeae in coffee and banana, P. pratensis and P.vulnus in fruits are serious problems.
The above ground symptoms caused by the nematode are non-specific in nature. The nematode usually infects in roots, rhizomes or tubers. Having penetrated into roots, they multiply in large numbers. All the stages of this nematode 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 symptoms. 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 are heavily impaired.
Management options1. Summer ploughing of field reduces nematode populations
2. Application of carbofuran (Furadan 3G ) at 1 kg a.i./ha at sowing reduces crop damage caused by soil nematodes
3.Growing antagonistic crop like marigold (Tagetes patula) cv. Harmony in autumn after main crop or in between rows of main crop.
4.Hot water treatment of bulbs, corms, tubers and fleshy roots can kill the dormant nematodes inside the root.
15. Pigeon pea cyst nematode (Heterodera cajani)
Heterodera cajani is the only species of cyst nematodes parasitizes a large number of leguminous crops. This nematode is prevalent and gaining importance in almost all pigeon pea growing states. Some populations of this nematode are known to attack sesame also. The species is distinctive for having large egg-sac (almost double of its cyst size). The nematode completes its life cycle in 16 days at 29 0C and in 45-80 day at 10 0C to 24 0C. It can also reproduce parthenogenetically, though it is bisexual species. During a cropping season, it can quickly multiply and build up a huge population. At seedling stage of plant pearl-like or lemon-shaped white female can be found attached with roots. Infected plants show yellowing, stunting, poor vigour and pod formation. Several crops like pigeonpea, cowpea, mungbean, soybean, blackgram and sesame are seriously damaged by the nematode.
Management options:
• Summer ploughing of fields during hot months
• Crop rotation with non host crops for 2-3 years
• Soil application of carbofuran (Furadan 3G) at 1-2 kg a. i / ha
• Bio-agent like Pasteuria penetrans (Pasutsuria 50WP) may be used to suppress soil population.
16.
Ectoparasitic nematodesSeveral ectoparasitic nematodes are emerging as new problems of crops. In spite of being numerous group in soil and attained much adaptive biological features of survival and multiplication as compared to endoparasites, they are regularly ignored as nematode pest. 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 and their pathogenic potential have been proved and their damaging nature are well documented. However, ectoparasitic nematodes are given least attention as because of their symptoms induced on plant are not easily convincing, 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 same crops, changes in cultivation practices like high yielding varieties, poor organic nutrition in soil, indiscriminate use of agrochemicals etc. resulted shift in pest status. For instances, Tylenchorhynchus brevilineatus, an polyphagy ectoparasite of diverse crops has appeared as serious problem as ‘kalahasti malady’ disease of groundnut in Andhra Pradesh accounting for 20 to 60% yield losses (Reddy et al.,1984). This nematode is also reported to cause concern in tobacco in Gujarat. There are many instances like T. brassicae in cabbage and cauliflower, Hoplolaimus indicus in rice and jute, Helicotylenchus multicintus in banana, Paratylenchus and Criconemoides in apple and peach, Xiphinema basiri and Hemicriconemoides in citrus and grape and Paralongidorus in sal are emerging nematode problems (Khan & Ganguly, 1995) in the changing agricultural scenario in India.
Management options• Ectoparasitic nematodes are very much vulnerable to summer ploughing which exposes and break the life cycle of many pathogens including nematodes.
• Crop rotation with poor hosts
Future approaches and conclusionPlant parasitic nematodes constitute one of the major limiting factors for cultivation of crops. The changes in agricultural situations have tremendous effects on the emergence of new nematode problems in India. The recent outbreak of M. graminicola in the Mandya district of Karnataka, West Bengal, Orissa, Assam, floral malady caused by Aphelenchoides besseyi in tuberose in West Bengal and Orissa, kalahasty malady in groundnut in Andhra Pradesh, Meloidogyne indica in kagzi lime in Gujarat and Pratylenchus zeae in maize are few examples of serious concern. Despite the fact, plant parasitic nematodes are mostly neglected and considered as low priority factor for crop production and protection In India. The economic significance of nematodes in agriculture is very often under estimated and their damage potential is not recognized by the plant protection specialists, scientists and administrators. As an important component of integrated pest management, nematode pathogens cannot be ignored and they could be tackled with the intelligent planning of nematode suppressive crop sequences, summer ploughing, organic manuring, clean cultivation, adjusting sowing time, water and irrigation management and sensible use of nematicides. The increasing concern on the ill effects of chemical pesticides on environment has driven the recent research interests on the use of several alternative strategies like botanicals, biopesticides and cropping system research for management of insect-pests diseases including nematodes. Some of the successes have been obtained for managing plant parasitic nematodes with neem based formulations, fungal formulation of P. lilacinus, bacterial formulations of Pasteuria penetrans and Pseudomonas fluorescens. However, wide application of bioagents in field scale is still limited probably due to their inconsistent efficacy in different agro-ecological situations. Integration of two or more methods can be explored on the basis of their compatibility, economic viability and availability to the farmers. Developing holistic approaches for managing field problems including nematodes inducing disease complexes in concert with other pathogens like fungi, bacteria and viruses will be the major future areas of research thrust.
Shortfalls of Nematology Extension:
1. Inadequate knowledge about nematode to the extension specialists
2. Ignorance of farmers, scientists and administrators about the nematode pathogen
3. Reluctance to give due importance of nematode problems in crops
4. Non acceptance of nematode pathogens as an important component of IPM
5. Lack of nematode specialists and their poor representation in different Government sponsored Training programmes organized by Extension Department/ Government Departments.
6. Non-availability of effective nematicides and a few or no pesticides industries are interested either to develop new molecules or judging their existing product having nematicidal properties.
7. Lack of coordination among the plant protection disciplines to resolve the field problems by developing a comprehensive package of practices.
Suggestions:
1. To create awareness among farmers and convince the authorities concerned about the potentialities of tiny worm to harm the crops.
2. Organizing group meetings of plant protection and production specialists and release a low cost publication for the farmers at least before Rabi and kharif season every year
3. Providing training lectures including practical problems by the Nematology specialist to the extension workers either separately or through routine training programmes organized by the Department,
Dr. Khan is a Reader of Nematology in the Department of Agricultural Entomology, Faculty of Agriculture, Bidhan Chandra Krishi Viswavidyalya(BCKV), Mohanpur, Nadia-741235, West Bengal, India. He has published more than 80 research papers in National and International Journals. He was the recepient of Youmg Scientist Award in 2005. His main interest is on working with nematode biosystematics, nematode problems of flower, rice, jute, tea and fruit crops. Recently eatblished a plant health clinic laboratory for extending Pest Advisory Services to the growers of West Bengal.
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