INTERACTION OF NEMATODES WITH OTHER ORGANISM.

INTERACTION OF PLANT PARASITIC NEMATODES WITH OTHER ORGANISM.

Plant parasitic nematodes favor the establishment of secondary pathogens viz., Fungi, bacteria, virus etc. The nematodes alter the host in such a way that the host tissue becomes suitable for colonization by the secondary pathogens. The nematode cause mechanical injury which favors the entry of microorganisms. The association of nematode and pathogen break the resistant in resistant cultivar of crop plant.
There are three type of Interaction.

1) Nematode - Fungal Interaction.
2) Nematode - Bacterium Interaction.
3) Nematode – Virus Interaction.

1. COURSE NO : PL-PATH-504 COURSE TITLE : Plant Nematology TOPIC : “INTERACTION OF PLANT PARASITIC NEMATODES WITH OTHER ORGANISMS” SUBMITTED TO : Dr. S. J. Magar SUBMITTED BY : Shaikh Abdul Kalam Shaikh Abdul Sami REG NO : 2023A/84ML Vasantrao Naik Marathawada Krishi Vidyapeeth,Parbhani College Of Agriculture, Latur

2. Plant parasitic nematodes favor the establishment of secondary pathogens viz., Fungi, bacteria, virus etc. The nematodes alter the host in such a way that the host tissue becomes suitable for colonization by the secondary pathogens. The nematode cause mechanical injury which favors the entry of microorganisms. The association of nematode and pathogen break the resistant in resistant cultivar of crop plant. There are three interactions : 1) Nematode - Fungal Interaction 2) Nematode - Bacterium Interaction 3) Nematode – Virus Interaction Nematode - Fungus Interaction Nematode - fungus interaction was first observed by Atkinson (1892) in cotton. Fusarium wilt was more severe in the presence of Meloidogyne spp. Since then the nematode - fungus interaction had received considerable attention on important crops like banana, cotton, cowpea, brinjal, tobacco and tomato. Some examples of nematode - fungus interaction are given in the following table.

3. Crop Name of the disease Nematode Fungus Role of nematode Cotton Damping off Meloidogyne incognita Meloidogyne incognita Rhizoctonia solani Pythium debarynum Assist Vascular wilt M. incognita Fusarium oxysporrum F. vasinfectum Assist Rotylenchulus reniformis Fusarium oxysporrum F. vasinfectum Assist Tobacco Dampink off Meloidogyne incognita Meloidogyne incognita Pythium debarynum Alternaria tenuis Assist Vascular wilt Meloidogyne incognita Meloidogyne incognita Fusarium oxysporrum Fusarium parasitica Assist Banana Vascular wilt Radopholus similis Fusarium oxysporrum Essential Tomato Cortical rot Globodera rostochinensis Rhizoctonia solani Assist Vascular wilt Meloidogyne spp. Fusarium oxysporrum Assist Potato Damping off Ditylenchus destructor Ppytophthora infestans Assist Cortical rot Globodera rostochinensis Globodera rostochinensis Rhizoctonia solani Verticillium dahliae Assist Onion Damping off Ditylenchus dispaci Botrytis allii Assist Brinjal Vascular wilt Pratylenchus penetrans Verticilllium dahliae Assist Pea Vascular wilt Pratylenchus spp. Fusarium oxysporrum Assist Pratylenchus penetrans Fusarium pisi Assist Soybean Damping off Meloidogyne javanica Rhizoctonia solani Assist Vascular wilt Heterodera glycines Fusarium spp. Assist Cow pea Vascular wilt Meloidogyne javanica Fusarium oxysporrum Assist wheat Stem rot Anguina tritici Dilophospora alopecuri Essential Wheat rot Heterodera avenae Rhizoctonia solani Assist

4. Nematode Fungus Interactions

5. Nematode Fungus Interactions The first record on the involvement of nematodes in disease complexes was reported in 1892, when atkinson observed that cotton wilt ( fusarium oxysporum f. Sp. Vasinfectum ) was more severe in the presence of root-knot nematode. Prior infection by nematodes results in drastic qualitative and quantitative changes in the root exudates of infected plants in the rhizosphere. Root-knot nematodes cause increased leakage of electrolytes from galled tissues which presumably activate the resting spores of pathogenic fungi. It is reported that in the first two weeks of infection, the galled roots exude more carbohydrates than in uninfected roots. Subsequently, protein and amino acid contents increase in exudates from galled roots. These changes in the nature of root exudates from infected plants influence the attraction and growth of fungi in the roots. The above observations are based on a detailed study on meloidogyne incognita and rhizoctonia solani interaction on tomato. Both fungus and exudates from nematode-infected roots are necessary for root rot disease to occur. The giant cells and galls induced by root-knot nematode provide a nutrient rich food base for fungal colonisation. Root-knot nematode infection on tobacco, cotton and peas increases in susceptibility to fusarium in much the same way. In a study involving peppermint grown by split-root technique, inoculation of pratylenchus sp. To one part of the root system predisposed the plants to verticillium fungus inoculated on a different part of the root system of the same plant .

6. The mechanical wounding by nematodes, or modification of host physiology or rhizosphere by nematodes is believed to be responsible for breakdown of genetic resistance in certain crop cultivars against fungal pathogens. Tobacco cultivars resistant to black shank disease (Phytophthora parasitica var. nicotianae ) succumbed to Wilt in the presence of root-knot nematode. Plant parasitic nematodes and mycorrhizal fungi share plant roots for space and nutrition. Mycelium feeding nematodes belonging to genera Ditylenchus, Aphelenchus and Aphelenchoides cause considerable reduction in mycorrhizal colonization; consequently, additional uptake of nutrients by the plants through mycorrhizal fungi decreases or ceases. Ectoparastic nematodes that feed upon root surface and root hairs directly affect the colonization of ectomycorrhizal fungi on the root surface. Several species of Tylenchorhynchus have been reported to suppress the colonization by Scleroderma species. Migratory endoparasitic nematodes such as Radopholus , Hirschmanniella , Pratylenchus spp . feed, migrate and form lesion inside the cortical tissues of host roots. Since mycorrhizal fungi also colonize the cortical region of roots, their sporulation, colonization and arbuscules may be adversely affected due to nematode activity. Sedentary endoparasitic nematodes, in general, less adversely affect mycorrhizal fungi than their migratory counterparts. In some cases, however, galls, syncytia and nurse cells induced by them do not support colonization and sporulation of mycorhhizal fungi like Glomus fasciculatum .

7. Nematode Bacterium Interactions

8. Crop Name of the disease Nematode Bacteria Role of nematode Wheat Tundu Anguina tritici Clavibactor tritici Essential Tobacco Vascular wilt Meloidogyne incognita Pseudomonas solanacearum Assist Tomato Vascular wilt Meloidogyne hapla Meloidogyne incognita Pseudomonas solanacearum Assist Helicotylenchus nannus Pseudomonas solanacearum Assist Canker Meloidogyne incognita Clavibactor michiganens Assist Potato Vascular wilt Meloidogyne spp. Pseudomonas solanacearum Assist 2) Nematode - Bacterium Interaction Nematode - bacterium interaction comparatively fewer than the nematode - fungal interactions. Some examples of nematode - bacterium interactions are presented in the following table.

9. Nematode Bacterium Interactions Injuries ( micropunctures ) caused by nematodes on root surface play a key role in inciting many bacterial diseases. These may provide increased opportunities for bacteria to enter the roots directly through these avenues, or the increased exudation through surface punctures may also attract and nourish bacteria at the site of punctures. Mechanical wounding (without nematodes) and the presence of Meloidogyne or Helicotylenchus increased bacterial wilt of carnations. Similarly, mechanically injured roots or roots with Meloidogyne sp. had higher incidence of wilt caused by Ralstonia solanacearum, compared to normal tobacco. In raspberry. Agrobacterium tumefaciens applied alone to roots resulted in no crown gall, but in the presence of Meloidogyne hapla , they induced crown gall. A second, pathologically more relevant interaction between foliar nematode Aphelenchoides ritzemabosil A. fragariae and bacterium ( Rhodococcus facians = Clavibacter fascians ) is evident on strawberry. Plants infected with nematodes alone are either symptomless or bear narrow ( alaminate ) leaves while bacteria alone also cause very little effect. But plants with both the organisma (bacteria carried by the nematode on its body surface) show varying degree of symptoms including 'cauliflower disease in extreme cases. Besides other deformities like stunting and malformation of flowers, such plants continually produce axillary buds in the crown, which give the appearance of small cauliflowers.

10. Association of seedgall nematode Anguina tritici with bacterium Clavibacter tritici ( Corynebacterium tritici ) in causing tundu or yellow ear rot disease of wheat is another such example. Nematodes alone cause carcockle discase, Bacterial cells are present in soil, on surface or inside the galls. The nematode acts as a vector carrying the bacterium on their surface. The tundu (yellow ear rot) disease can not develop without the involvement of nematode. Rathayibacter toxicus ( Clavibacter toxicus , Corynebacterium toxicus ) is carried by second stage juveniles of Anguina funestra and A. agrostis on to the floral parts of fodder grasses (Lolium spp., Polypogon monspeliensis , Lachnagrostis sp .) in Australia and South Africa. Cattle and sheep feeding upon the inflorescence of these grasses suffer from nervous breakdown due to toxins produced by the bacteria. This disease in livestock is known as Annual Rye Grass Toxicity. The antagonistic role of nematodes has been established in several cases of symbiotic Rhizobium-leguminous plant systems. Soybean plants infected with Heterodera glycines (race 1) suffer heavily in terms of nitrogen fixation by Rhizobium. The number and size of nodules is drastically reduced. Roots with H. glycines had only one-twentieth the number and about one-fifth the weight of nodules as compared to uninfected plants. Meloidogyne spp. are known to parasitize nodules themselves and destroy them. Phytonematode species, however, differ in their capability to adversely affect nodulation in plants.

11. Nematode Virus Interactions

12. NEPO Virus Nematode Arabis mosaic Xiphinema diversicaudatum X. paraelongatum Grapevine fan leaf X. index Grapevine yellow mosaic X. index Tobaco ring spot X. americanum Cowpea mosaic X. basiri Tomato black ring, beet ring spot L. elongates Tomato black ring, lettuce ring spot L. attenuatus NETU Virus Nematode Tobacco rattle Paratrichodorus P. allius , P. nanus P. porosus , P. teres Trichodorus christei T. primitivus , T. cylindricus T. hooperi T. minor, T. similes Pea early browning P. anemones, P. pachydermus P. teres, T. viruliferus Nematode - Virus Interaction In nematode - virus complex, nematode serves as a vector. Numerous virusnematode complexes have been identified after the pioneer work by Hewit , Raski and Goheen (1958) who found that Xiphinema index was a vector of grapevine fan virus. Xiphinema,Longidorus , Paralongidorus spp. transmits the ring spot viruses called NEPO derived from nematode transmitted polyhedral shaped particles. Trichodorus spp. and Paratrichodorus spp. transmitted rattle virus called NETU derived from nematode transmitted tubular shape virus particles. All these nematodes have modified bottle shape oesophagus . The nematodes acquire and transmit the virus by feeding required little one day. Once acquired it persist for longer time in nematode body e.g. Grapevine fan leaf virus will exist upto 60 days in X. index

13. Nematode Virus Interactions Plant parasitic nematodes had long been suspected to act as vectors of soil-borne viruses due to their subterranean mode of life and root parasitism. It was only in 1958 that hewitt , raski and goheen experimentally proved that xiphinema index transmits grapevine fanleaf virus (GFLV), presently species of xiphinema , longidorus , trichodorus and paratrichodorus are known to act as vectors. Interestingly, all these genera belong to order dorylaimida whereas majority of plant parasites are members of order tylenchida . All the virus vector genera are cetoparasites of roots, cosmopolitan in distribution and have moderate to wide host range. Viruses: viruses transmitted by nematodes are RNA viruses. They also have moderate to wide plant host range, and are transmitted by nematodes, seeds, pollens, etc. They are broadly classified into two groups according to the size and shape of virus particle. 1. NEPO (nematode transmitted polyhedral particles) viruses : They measure 25-30 nm ( inm 10 metre) in size, are polyhedral in shape and are transmitted by species of xiphinema and longidorus , e.G. GFLV, tomato ring spot virus (TRSV). 2. TOBRA of NETU (nematode transmitted tubular particles ) viruses : These rod shaped viruses are transmitted by species of trichodoras and paratrichodorus . There are three main groups of these viruses which differ in size and host response tobacco rattle virus (TRV), pea early browning virus (PEBV), and pepper ringspot virus (PRV).

14. Steps involved in Virus Transmission Acquisition : nematodes become viruliferous when they feed upon virus infected roots. Viruses enter nematode body along with cell sap. All the four juvenile stages and adults of both the sexes are capable of acquiring and transmitting the viruses. Retention : viruses passing through the stomodaeum along with the ingested food are selectively adsorbed on the cuticular lining of the stomodaeum. Sites of viral retention differ among genera (fig. 8.2). In case of xiphinema species the viruses are retained on the cuticular lining of lumen of odontophore (stylet extension) and oesophagus, and in longidorus on guiding sheath and odontostyle . TOBRA viuses are retained on the cuticular lining of oesophageal lumen of trichodorus and paratrichodorus . Viral particles can be retained inside the nematode body for weeks together. However, the viral particles are shed off along with old cuticle during moulting these particles do not multiply inside the nematode body Dissociation : viral particles get separated from the site of retention when the saliva (oesophageal gland secretion) passes through stomodacum during salivation. This process is very slow and all the viral particles are not released simultaneously. Inoculation: viruses enter inside the new plant host along with saliva when viruliferous nematode feeds upon it. Inoculation : viruses enter inside the new plant host along with saliva when viruliferous nematode feeds upon it.

15. Specificity of Transmission Virus transmission is specific, i.E. , All the nematodes cannot transmit all the viruses and vice versa, e.G. , X. Index transmits GFLV but cannot transmit cherry leafroll virus. This specificity is determined by the chemical nature of lining of cuticle at site of retention, and chemical nature of protein coat of virus. One of the puzzling questions had been why tylenchids , which constitute major group of plant parasitic nematodes, do not transmit viruses. It may be due to: 1) difference in the chemical nature of cuticular lining of stomodacum , 2) very little space available for virus adsorption and dissociation as the lumen of dorsal oesophageal gland empties just posterior to the stylet knobs in tylenchids , and 3) contents of saliva may inactivate viruses. Table 1.4: An analysis of possible plant nematode relationships given as below (source: sasser and jenkins , 1900)

16. An association is found between a nematode and a diseased condition of roots, but fungi, bacteria and other factors may be involved The nematode occurs in necrotic areas but is unable to attack living plant tissue   The nematode (a) is morphologically adapted for parasitiem (b) penetrates and colonises or fee feeds upon living plant material (c) reproduces within or upon the host   Any nematode which, while present in a necrotic area formed by an incitant or pathogen releases metabolic by-products capable of killing host cells directly and/or predisposing unaffected host cells to invasion by microorganisms and/or stimulating the growth of harmful microorganisms A nematode which carries a pathogen into host tissue but is not further involved in the etiology of the disease A perasitic nematode which attacks healthy plant tissue which, forming infection courts for other organisms but by itself, cannot cause disease A parasitic nematode which can cause the disease in the absence of all other organisms PLANT PARASITES OTHERS Biology PATHOGEN AGGRAVATOR RELETIONSHIP VECTOR INCITANT Ec ology Eti ology

17. Fig. 1.1 Anterior portion of nematode vectors (A- Xiphinema , B- Longidorus , C- Trichodorus and Paratnchodorus spp .) of plant viruses: red portion indicates parts where vinus particles retained Acquisition     Retention Inoculation     Dissociation B- Longidorus A- Xiphinema C- Trichodorus and Paratnchodorus spp .

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