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Root-knot nematode

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Root-knot nematode
Larva of root-knot nematode,Meloidogyne incognita,magnified 500×, shown here penetrating atomatoroot
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Nematoda
Class: Secernentea
Order: Tylenchida
Family: Heteroderidae
Genus: Meloidogyne
Göldi,1892
Species

See text

Root-knot nematodesare plant-parasiticnematodesfrom the genusMeloidogyne.They exist insoilin areas with hot climates or short winters. About 2000 plants worldwide are susceptible to infection by root-knot nematodes and they cause approximately 5% of globalcrop loss.[1]Root-knot nematodelarvaeinfect plantroots,causing the development of root-knotgallsthat drain the plant's photosynthate and nutrients. Infection of young plants may be lethal, while infection of mature plants causes decreased yield.

Economic impact

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Root-knot nematodes (Meloidogynespp.) are one of the three most economically damaging genera of plant-parasitic nematodes on horticultural and field crops. Root-knot nematodes are distributed worldwide, and are obligate parasites of the roots of thousands of plant species, includingmonocotyledonousanddicotyledonous,herbaceous and woody plants. The genus includes more than 90 species,[2]with some species having several races. FourMeloidogynespecies (M. javanica,M. arenaria,M. incognita,andM. hapla) are major pests worldwide, with another seven being important on a local basis.[3]Meloidogyneoccurs in 23 of 43 crops listed as having plant-parasitic nematodes of major importance, ranging from field crops, through pasture and grasses, to horticultural, ornamental and vegetable crops.[4]If root-knot nematodes become established in deep-rooted,perennialcrops, control is difficult and options are limited.[citation needed]

Meloidogynespp. were first reported incassavaby Neal in 1889.[5]Damage oncassavais variable depending on cultivar planted, and can range from negligible to serious.[6]Early-season infection leads to worse damage.[7]In most crops, nematode damage reduces plant health and growth; in cassava, though, nematode damage sometimes leads to increased aerial growth as the plants try to compensate. This possibly enables the plant to maintain a reasonable level of production. Therefore, aerial correlations to nematode density can be positive, negative or not at all.[8]Vegetablecrops grown in warm climates can experience severe losses from root-knot nematodes, and are often routinely treated with a chemicalnematicide.Root-knot nematode damage results in poor growth, a decline in quality and yield of the crop and reduced resistance to other stresses (e.g.drought,other diseases). A high level of damage can lead to total crop loss. Nematode-damaged roots do not use water and fertilisers as effectively, leading to additional losses for the grower. In cassava, it has been suggested that levels ofMeloidogynespp. that are sufficient to cause injury rarely occur naturally.[8]However, with changing farming systems, in a disease complex or weakened by other factors, nematode damage is likely to be associated with other problems.[9]

Root-knot galls

Control

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Root-knot nematodes can be controlled with biocontrol agentsPaecilomyces lilacinus,Pasteuria penetrans[10]andJuglone.[11]

Life cycle

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All nematodes pass through anembryonicstage, fourjuvenilestages (J1–J4) and an adult stage. JuvenileMeloidogynesparasites hatch fromeggsas vermiform, second-stage juveniles (J2), the firstmoulthaving occurred within the egg. Newly hatched juveniles have a short free-living stage in the soil, in therhizosphereof the host plants. They may reinvade the host plants of their parent or migrate through the soil to find a new host root. J2 larvae do not feed during the free-living stage, but uselipidsstored in the gut.[3]

An excellent model system for the study of the parasitic behaviour of plant-parasitic nematodes has been developed usingArabidopsis thalianaas a model host.[12]TheArabidopsisroots are initially small and transparent, enabling every detail to be seen. Invasion and migration in the root was studied usingM. incognita.[13]Briefly, second stage juveniles invade in the root elongation region andmigratein the root until they became sedentary. Signals from the J2 promoteparenchymacells near the head of the J2 to becomemultinucleate[14]to form feeding cells, generally known as giant cells, from which the J2 and later the adults feed.[15]Concomitant with giant cell formation, the surrounding root tissue gives rise to a gall in which the developing juvenile is embedded. Juveniles first feed from the giant cells about 24 hours after becoming sedentary.[citation needed]

After further feeding, the J2s undergo morphological changes and become saccate. Without further feeding, they moult three times and eventually become adults. In females, which are close to spherical, feeding resumes and the reproductive system develops.[3]The life span of an adult female may extend to three months, and many hundreds of eggs can be produced. Females can continue egg laying after harvest of aerial parts of the plant and the survival stage between crops is generally within the egg.[citation needed]

The length of the life cycle is temperature-dependent.[16][17]The relationship between rate of development and temperature is linear over much of the root-knot nematode life cycle, though it is possible the component stages of the life cycle, e.g. egg development, hostroot invasionor growth, have slightly different optima. Species within the genusMeloidogynealso have different temperature optima. InM. javanica,development occurs between 13 and 34 °C, with optimal development at about 29 °C.[18]

Gelatinous matrix

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Root-knot nematode females lay eggs into a gelatinous matrix produced by six rectal glands and secreted before and during egg laying.[19]The matrix initially forms a canal through the outer layers of root tissue and later surrounds the eggs, providing a barrier to water loss by maintaining a high moisture level around the eggs.[20]As the gelatinous matrix ages, it becomes tanned, turning from a sticky, colourless jelly to an orange-brown substance which appears layered.[21]

Egg formation and development

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Egg formation inM. javanicahas been studied in detail,[22]and is similar to egg formation in the well studied, free-living nematodeCaenorhabditis elegans.[23]Embryogenesis has also been studied, and the stages of development are easily identifiable with a phase contrast microscope following preparation of an egg mass squash. The egg is formed as one cell, with two-cell, four-cell and eight-cell stages recognisable. Further cell division leads to the tadpole stage, with further elongation resulting in the first stage juvenile, which is roughly four times as long as the egg. The J1 stage ofC. eleganshas 558 cells, and the J1 ofM. javanicalikely has a similar number, since all nematodes are morphologically and anatomically similar.[23]The egg shell has three layers, with the vitelline layer outermost, then achitinouslayer and a lipid layer innermost.

Egg hatching

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Preceded by induced changes in eggshellpermeability,hatching may involve physical and/or enzymatic processes in plant-parasitic nematodes.[24]Cyst nematodes,such asGlobodera rostochiensis,may require a specific signal from the rootexudatesof the host to trigger hatching. Root-knot nematodes are generally unaffected by the presence of a host, but hatch freely at the appropriate temperature when water is available. However, in an egg mass orcyst,not all eggs will hatch when the conditions are optimal for their particular species, leaving some eggs to hatch at a later date.Ammoniumionshave been shown to inhibit hatching and to reduce the plant-penetration ability ofM. incognitajuveniles that do hatch.[25]

Reproduction

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Root-knot nematodes exhibit a range of reproductive modes, including sexuality (amphimixis),facultative sexuality,meiotic parthenogenesis (automixis) and mitotic parthenogenesis (apomixis).

Species

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References

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  1. ^Sasser JN, Carter CC: Overview of the InternationalMeloidogyneProject 1975–1984. In An Advanced Treatise onMeloidogyne.Edited by: Sasser JN, Carter CC. Raleigh: North Carolina State University Graphics; 1985:19–24.
  2. ^Moens, Maurice, Roland N Perry, and James L Starr. 2009. "Meloidogyne Species: a Diverse Group of Novel and Important Plant Parasites." In Root-knot Nematodes, ed. Roland N Perry, Maurice Moens, and James L Starr, 1–17. Wallingford, UK: CABI Publishing.
  3. ^abcEisenback, J. D. & Triantaphyllou, H. H. 1991 Root-knot Nematodes:Meloidogynespecies and races. In: Manual of Agricultural Nematology, W. R. Nickle. (Ed). Marcel Dekker, New York. pp 281–286.
  4. ^Stirling, G. R.; Stanton, J. M.; Marshall, J. W. (1992). "The importance of plant-parasitic nematodes to Australian and New Zealand agriculture".Australasian Plant Pathology.21(3): 104–115.doi:10.1071/app9920104.S2CID30012090.
  5. ^Neal, J. C. 1889. The root-knot disease of the peach, orange and other plants in Florida due to the work ofAnguillulaBull. I.S. Bur. Ent.20.31pp.
  6. ^Jatala, P., bridge, J. 1990. Nematode parasites of root and tuber crops. InPlant parasitic nematodes in sub-tropical and tropical agriculture., pp 137-180. Luc, M., Sikora, R.A., Bridge, J., CABI Publishing, Wallingford, UK.
  7. ^Makumbi-kidza, N. N., Speijer and Sikora R. A. 2000. Effects ofMeloidogyne incognitaon growth and storage-root formation of cassava (Manihot esculenta). J Nematol.; 32(4S): 475–477.
  8. ^abGapasin, R.M. 1980. Reaction of golden yellow cassava toMeloidogynespp. Inoculation. Annals of Tropical Research 2:49–53.
  9. ^Theberge, R. L. (eds). 1985. Common African Pests and Diseases of cassava, Yam, Sweet Potato and Cocoyam. International Institute of Tropical Agriculture (IITA). Ibadan, Nigeria 107 p.
  10. ^Charles, Lauren; Carbone, Ignazio; Davies, Keith G.; Bird, David; Burke, Mark; Kerry, Brian R.; Opperman, Charles H. (2005)."Phylogenetic analysis ofPasteuria penetransby use of multiple genetic loci ".Journal of Bacteriology.187(August 2005): 5700–5708.doi:10.1128/JB.187.16.5700-5708.2005.PMC1196054.PMID16077116.
  11. ^Dama, L.B.; Poul, B.N.; Jadhav, B.V.; Hafeez, M.D. (1999). "Effect of Herbal" Juglone "on Development of the plant parasitic nematode (Meloidogynespp.) onArachis hypogaea".Journal of Ecotoxicology and Environmental Monitoring.9:73–76.
  12. ^Sijmons, P. C.; Grundler, F. M. W.; von Mende, N.; Burrows, P. R.; Wyss, U. (1991). "Arabidopsis thallianaas a new model host for plant-parasitic nematodes ".The Plant Journal.1(2): 245–254.doi:10.1111/j.1365-313x.1991.00245.x.
  13. ^Wyss, U., Grundler, F.M.W. & Munch, A. 1992 The parasitic behaviour of second stage juveniles ofMeloidogyne incognitain roots ofArabidopsis thaliana.Nematologica, 38, 98–111.
  14. ^Hussey, R. S. & Grundler, F. M. W. 1998 Nematode parasitism of plants. In: The Physiology and Biochemistry of free-living and plant-parasitic nematodes. Perry, R. N. & Wright, D. J. (Eds), CABI Publishing, UK. pp 213 – 243.
  15. ^Sijmons, P. C.; Atkinson, H. J.; Wyss, U. (1994). "Parasitic strategies of root nematodes and associated host cell responses".Annual Review of Phytopathology.32:235–259.doi:10.1146/annurev.phyto.32.1.235.
  16. ^Madulu, J. & Trudgill, D. L. 1994 Influence of temperature onMeloidogyne javanica.Nematologica, 40, 230–243.
  17. ^Trudgill, D. L. 1995 An assessment of the relevance of thermal time relationships to nematology. Fundamental and Applied Nematology, 18, 407–417.
  18. ^Bird, A. F.; Wallace, H.R. (1965). "The Influence of Temperature On Meloidogyne Hapla and M. Javanica".Nematologica.11(4): 581–589.doi:10.1163/187529265X00726.
  19. ^Maggenti, A. R. & Allen, M. W. 1960 The origin of the gelatinous matrix inMeloidogyne.Proceedings of the Helminthological Society of Washington, 27, 4–10.
  20. ^Wallace, H. R. 1968 The influence of soil moisture on survival and hatch ofMeloidogyne javanica.Nematologica, 14, 231–242.
  21. ^Bird, A. F. 1958 The adult female cuticle and egg sac of the genusMeloidogyneGoeldi, 1887. Nematologica, 3, 205–212.
  22. ^McClure, M. A.; Bird, A. F. (1976). "The tylenchid (Nematoda) egg shell: formation of the egg shell inMeloidogyne javanica".Parasitology.72:29–39.doi:10.1017/s003118200004316x.S2CID84455043.
  23. ^abWood, W. B. 1988 Introduction to C.elegans. In::The NematodeCaenorhabditis elegans,W. B. Wood (Ed), Cold Spring Harbour Laboratory, New York. pp 1–16.
  24. ^Norton, D. C. & Niblack, T. L. 1991 Biology and ecology of nematodes. In: Manual of Agricultural Nematology, Nickle, W. R. (Ed), Marcel Dekker, New York. pp 47–68.
  25. ^Surdiman; Webster, J. M. (1995)."Effect of ammonium ions on egg hatching and second-stage juveniles ofMeloidogyne incognitain axenic tomato root culture ".Journal of Nematology.27(3): 346–352.PMC2619617.PMID19277298.
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