lecture 5 classification of nematodes on the basis of phytoparasitism 6/14/2014walia ccshau1

Lecture 5

Classification of Nematodes on the basis of Phytoparasitism

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Habitat

• Majority (90%) of PPNs attack roots or other below ground plant parts such as tubers, rhizomes, suckers, bulbs etc.– Ectoparasites 60%– Endoparasites 30%

• Only a few forms (10%) attack above ground parts such as leaves, stems, buds, inflorescence etc.– Ectoparasites 2%– Endoparasites 8%

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Parasites of below ground part parts

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Ectoparasites• Spend entire life cycle in soil, all life cycle stages, including

eggs in soil• Only stylet is inserted into roots, body remains outside• A vast majority of ectoparasites feed on root hairs and

epidermal cells• Not considered very damaging, except for some groups

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Ectoparasites

• Migratory (Vagrant ectoparsites)– Feed at a particular site very briefly and then move to

another site– Remain vermiform, eggs scattered in soil– Examples

• Awl nematode, Dolichodorus• Sting nematode, Belonolaimus• Dagger nematode, Xiphinema• Needle nematode, Longidorus• Stubby root nematode, Trichodorus, Paratrichodorus

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Ectoparasites• Sedentary (Sessile) ectoparasites

– Feed at a site for long period – Very sluggish in movement– Have coarse striation or annulations on cuticle– Criconematid group having small bodies and long

stylets relative to their body fall in this category– May secrete an adhesive plug to fix the stylet into the

root– Examples

• Sheath nematode, Hemicycliophora arenaria• Sessile nematode, Cacopaurus pestis

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Semi-endoparsites

The anterior portion of the body is embedded into the plant tissues

• Migratory semi-endoparasites– Remain vermiform– Do not establish a permanent feeding site in plant

tissues– Rarely the entire body may be inside the plant tissues– Examples

• Spiral nematode, Helicotylenchus• Lance nematode, Hoplolaimus• Stunt or Stylet nematode, Tylenchorhynchus group

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Semi-endoparasites

• Sedentary semi-endoparasites– Establish a permanent feeding site inside plant tissues– Do not move after infection– Eggs are deposited in masses around the body of

females; fecundity is more - about 40-80 eggs per female

– The posterior part of females outside the root becomes swollen to varying degrees

• Citrus nematode, Tylenchulus semipenetrans• Reniform nematode, Rotylenchulus reniformis

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Sedentary Semi-endoparasites• Examples

– Reniform nematode, Rotylenchulus reniformis

– Citrus nematode, Tylenchulus semipenetrans

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Endoparasites• Migratory endoparasites

– All stages (except egg) can cause infection, and are present in soil initially

– Complete the entire life cycle in side plant tissues– Feeding, migration, growth, reproduction, and oviposition take

place in plant tissues– Biological activities confined to cortex only; eggs are laid

scattered, fecundity around 25 eggs per female– Do not induce any special feeding area– Any stage can leave the roots and come out into the soil due

crop senescence of tissue destruction• Lesion or Meadow nematode, Pratylenchus• Rice root nematode, Hirschmanniella• Burrowing nematode, Radopholus

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Migratory Endoparasites

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Endoparasites• Sedentary endoparasites

– Evolutionary most advanced and most damaging among all PPNs

– Only a particular stage (J2) of life cycle infective– Induce special feeding areas, involving vascular tissues– Females become swollen to varying degrees after

infection and do not move– Eggs laid in masses either inside the female body or

outside in an eggmass– Fecundity is high (200-500 eggs per female)

• Root-knot nematode, Meloidogyne • Cyst nematode, Heterodera, Globodera

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Sedentary Endoparasites

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Parasites of above ground plant parts

• Specially adapted to feed on leaves, stems, buds, inflorescence etc.

• May feed ecto- or endoparasitically• Do not produce any special feeding area• Can crawl up the plant in a thin film of water• Eggs are deposited in plant tissues• Usually undergo anhydrobiosis at crop maturity or

under moisture stress; a particular stage of life cycle only undergoes quiescence

• Can remain dormant for varying periods, revive upon availability of moisture

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Anhydrobiosis

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Parasites of above ground plant parts

• Gall forming– Wheat seed gall nematode, Anguina tritici– Leaf gall nematode, Anguina balsamophila

• Non-gall forming– Stem nematode, Ditylenchus dipsaci, D. angustus– Foliar nematode, Aphelenchoides fragariae,

A. ritzemabosi• Associates of insects

– Pine wood nematode, Bursaphelenchus xylophilus– Red ring nematode, Bursaphelenchus cocophilus

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