ENDOPARASITES

ECTOPARASITES

Root-lesion nematodes

Dagger nematodes

Root-knot nematodes

Reniform nematodes

Nematode DamageNematode Damage Rarely, does a single nematode pose Rarely, does a single nematode pose

a threat to a plant. (exceptions - virus a threat to a plant. (exceptions - virus vectors and sting nematodes)vectors and sting nematodes)

Damage to plant parts results from Damage to plant parts results from many nematodes feeding at once. many nematodes feeding at once. The root system of plants can be The root system of plants can be

growing in the presence of hundreds of growing in the presence of hundreds of thousands or even millions of thousands or even millions of nematodes. nematodes.

Nematode DamageNematode Damage Quite often it is very difficult to see Quite often it is very difficult to see

symptoms caused by nematode (even symptoms caused by nematode (even though yield loss may be reduced by though yield loss may be reduced by 30%). 30%).

This is compounded by the fact that This is compounded by the fact that nematodes are rarely normally nematodes are rarely normally distributed in a field. distributed in a field.

Nematode damage can be confused with Nematode damage can be confused with herbicide and other chemical injury. herbicide and other chemical injury.

DamageDamageMechanical injury results from the nematode stylet puncturing the cell Mechanical injury results from the nematode stylet puncturing the cell

wall, and is followed by the secretion of enzymes and nutrient wall, and is followed by the secretion of enzymes and nutrient extraction. This process leaves cells that are damaged or extraction. This process leaves cells that are damaged or completely destroyed. completely destroyed. 

Nematode damage can result in a variety of symptoms: Nematode damage can result in a variety of symptoms: 1. Lesions1. Lesions2. Galls or swellings 2. Galls or swellings 3. Stunted plants3. Stunted plants4. Loss of vigor4. Loss of vigor5. Excessive root branching 5. Excessive root branching 6. Twisted or distorted stems and/or leaves 6. Twisted or distorted stems and/or leaves 7. Disruption in flower development / sterility 7. Disruption in flower development / sterility 8. Dead or incapacitated root tips8. Dead or incapacitated root tips

Disease Complexes - While nematodes are devastating pathogens, Disease Complexes - While nematodes are devastating pathogens, their most significant influence in agriculture results from their their most significant influence in agriculture results from their participation in pathogen complexes. participation in pathogen complexes. 

DamageDamageNematodes and viruses - Nematodes can serve as Nematodes and viruses - Nematodes can serve as

vectors for as many as 28 viruses, virus retention vectors for as many as 28 viruses, virus retention can last until molting and viruses cannot be passed can last until molting and viruses cannot be passed to offspring. to offspring. 

• TrichodorusTrichodorus spp. spp. -  Stubby-root nematodes-  Stubby-root nematodes• Netuviruses (NETU) rod-shaped - tobacco rattle Netuviruses (NETU) rod-shaped - tobacco rattle

virus, pea early browning virusvirus, pea early browning virus

• XiphenemaXiphenema spp. – Dagger nematodes spp. – Dagger nematodes• Nepoviruses (NEPO) have a polyhedral shape - Nepoviruses (NEPO) have a polyhedral shape -

grapevine fanleaf virus, tomato ringspot virus grapevine fanleaf virus, tomato ringspot virus

DamageDamage

DamageDamage

TaxonomyTaxonomyKingdom AnimaliaKingdom AnimaliaPhylum NemataPhylum NemataClass Secernentea Class Secernentea 5 other orders contain free-living forms and parasites of 5 other orders contain free-living forms and parasites of

animalsanimals

Order Aphelenchida - parasites of higher plants (usually on Order Aphelenchida - parasites of higher plants (usually on above ground parts), fungi, and insectsabove ground parts), fungi, and insects

Important genera:Important genera:AphelenchoidesAphelenchoides - foliar nematode - foliar nematode BersaphelenchusBersaphelenchus - pine wilt nematode- pine wilt nematode

Order Tylenchida - parasites of higher plants, insects, and Order Tylenchida - parasites of higher plants, insects, and fungi – largest % of plant pathogensfungi – largest % of plant pathogens

Important genera:Important genera:HeteroderaHeterodera spp. - cyst nematodesspp. - cyst nematodesMeloidogyneMeloidogyne spp. - root-knot nematodes spp. - root-knot nematodesPratylenchusPratylenchus spp. - root-lesion nematodes spp. - root-lesion nematodes

TaxonomyTaxonomyKingdom AnimaliaKingdom AnimaliaPhylum NemataPhylum NemataClass AdenophoreaClass Adenophorea  (as opposed to Secernentea)(as opposed to Secernentea)

11 other orders contain free-living forms and 11 other orders contain free-living forms and parasites of animals and microorganismsparasites of animals and microorganisms

Order Dorylaimida - plant parasites/virus vectorsOrder Dorylaimida - plant parasites/virus vectors(Stylet without knobs and no distinct median (Stylet without knobs and no distinct median

bulb)bulb)Important genera:Important genera:

XiphinemaXiphinema spp.- dagger nematode spp.- dagger nematode LongidorusLongidorus sppspp.- .- needle nematode needle nematode TrichodorusTrichodorus spp. spp.- - stubby-root nematodestubby-root nematode

Root lesion nematodesRoot lesion nematodes PratylenchusPratylenchus spp. spp.

7 important species in United States7 important species in United States Most plants are susceptible to one or more Most plants are susceptible to one or more

speciesspecies Migratory endoparasite, can leave and reenter Migratory endoparasite, can leave and reenter

the roots many times in its lifecycle. the roots many times in its lifecycle. Males may or may not participate in Males may or may not participate in

reproduction.reproduction.

Root lesion nematodesRoot lesion nematodes

Root-knot nematodeRoot-knot nematode MeloidogyneMeloidogyne spp. spp.

M. incognitaM. incognita – southern-root knot – southern-root knot M. haplaM. hapla – northern root-knot – northern root-knot All are sedentary, endoparasitesAll are sedentary, endoparasites

After J2 stage enters the root and establishes giant cells After J2 stage enters the root and establishes giant cells (cells enlarge and rapidly divide) creating a more efficient (cells enlarge and rapidly divide) creating a more efficient nutrient sink for the nematode = gall production.nutrient sink for the nematode = gall production.

After the J2 becomes an adult, males leave the root. The After the J2 becomes an adult, males leave the root. The

female will swell upon maturity producing several hundred female will swell upon maturity producing several hundred

eggs. Males may or may not participate in reproduction.eggs. Males may or may not participate in reproduction.

Population is managed by the ratio of females : males that Population is managed by the ratio of females : males that

are produced. Immature females can change to males if are produced. Immature females can change to males if

the population density can not be supported. the population density can not be supported.

Root-knot nematodeRoot-knot nematode

Root-knot nematodeRoot-knot nematode

Juveniles in root Male, hatching from cuticle

Giant cell

Gall, with female protruding

Root-knot nematodeRoot-knot nematode

Root-knot NematodeRoot-knot Nematode

Cyst nematodesCyst nematodes HeteroderaHeterodera spp. spp.

H. schactii H. schactii – sugar beet cyst nematode– sugar beet cyst nematode H. glycines – H. glycines – soybean cyst nematode – $3 billion in soybean cyst nematode – $3 billion in

damage/yeardamage/year All are sedentary, endoparasitesAll are sedentary, endoparasites

After J2 stage enters the root and establishes a smaller feeding After J2 stage enters the root and establishes a smaller feeding site than root-knot nematode. No gall production. site than root-knot nematode. No gall production.

After the J2 becomes an adult, males leave the root to fertilize After the J2 becomes an adult, males leave the root to fertilize

the females that have protruded through the root. the females that have protruded through the root.

The female will swell upon maturity producing several hundred The female will swell upon maturity producing several hundred

eggs outside and inside of her body. When she dies (4 wks old) eggs outside and inside of her body. When she dies (4 wks old)

her body will become a protective cyst for her young. her body will become a protective cyst for her young.

Some eggs will hatch immediately, some later in the season, Some eggs will hatch immediately, some later in the season,

next year or years, or never. next year or years, or never.

Soybean cyst nematodeSoybean cyst nematode

Soybean cyst nematode Soybean cyst nematode No visible symptomswith 30% yield loss

Visible symptomswith 60 -80% yield loss

Dagger nematodesDagger nematodes Xiphinema Xiphinema spp.spp.

3 important species in United States3 important species in United States Characterized by long body and stylet.Characterized by long body and stylet. Sedentary ectoparasite. Feeds only at the root Sedentary ectoparasite. Feeds only at the root

tips. tips. Feeding produces knobby, stunted roots. Feeding produces knobby, stunted roots. Males are required for reproduction, females Males are required for reproduction, females

produce very few eggs, but lives several months produce very few eggs, but lives several months (most other nematodes live a few weeks). (most other nematodes live a few weeks).

Dagger nematodesDagger nematodes

Dagger nematodesDagger nematodes

Stunted plants

Stubby roots

Dagger nematodes Dagger nematodes (grape fan leaf (grape fan leaf virus)virus)

Management StrategiesManagement Strategies

I. Cultural practices - Includes agricultural tactics that I. Cultural practices - Includes agricultural tactics that indirectly influence pathogen populations and indirectly influence pathogen populations and communities.communities.

a. Crop rotationa. Crop rotation

b. Trap cropsb. Trap crops

c. Fallow c. Fallow

e. Flooding or heate. Flooding or heat

f. Tillage f. Tillage

g. Planting date   g. Planting date  

Management Strategies Management Strategies II. Breeding for resistanceII. Breeding for resistanceThe use of nematode resistant varieties is a major The use of nematode resistant varieties is a major

management strategy.  In many crops, chemical control management strategy.  In many crops, chemical control is not economically viable and breeding is the only is not economically viable and breeding is the only available tactic.  available tactic.    

One of many limitations is that where races of nematodes One of many limitations is that where races of nematodes are problematic (such as soybean cyst nematode and are problematic (such as soybean cyst nematode and root-knot nematode), effective control of nematode root-knot nematode), effective control of nematode populations occurs only when the plant contains populations occurs only when the plant contains resistant genes against the specific race present.resistant genes against the specific race present.

Management StrategiesManagement StrategiesIII. BiocontrolIII. BiocontrolThe use of fungi, bacteria, viruses, other nematodes,to The use of fungi, bacteria, viruses, other nematodes,to

manage nematodes.  The are many examples of manage nematodes.  The are many examples of biocontrol of nematodes, however, very few work in biocontrol of nematodes, however, very few work in the field. the field.

  Bacterium - endospore forming Bacterium - endospore forming PasteuriaPasteuria penetranspenetransFungus - adhesive rings by Fungus - adhesive rings by ArthrobotrysArthrobotrys spp. spp.

Management StrategiesManagement StrategiesIV. Chemical controlIV. Chemical controlThe use of pesticides or other chemicals to reduce The use of pesticides or other chemicals to reduce

or eliminate nematode populations.or eliminate nematode populations.

Nematicides - are used to manage nematode Nematicides - are used to manage nematode populations on high value crops.  The use of populations on high value crops.  The use of nematicides is being reduced because of toxicity nematicides is being reduced because of toxicity to the environment and to humans.to the environment and to humans.

examples – Methyl Bromide, Vapam, Telone, Temik, examples – Methyl Bromide, Vapam, Telone, Temik, Mocap, CounterMocap, Counter