ENDOPARASITES

Root-lesion nematodes Root-knot nematodes Dagger nematodes

ECTOPARASITES

Reniform nematodes

 

Nematode Damage Rarely, does a single nematode pose a threat to a plant. (exceptions - virus vectors and sting nematodes) Damage to plant parts results from many nematodes feeding at once.

 The root system of plants can be growing in the presence of hundreds of thousands or even millions of nematodes.

Nematode Damage

 Quite often it is very difficult to see symptoms caused by nematode (even though yield loss may be reduced by 30%).  This is compounded by the fact that nematodes are rarely normally distributed in a field.  Nematode damage can be confused with herbicide and other chemical injury.

Damage

Mechanical injury results from the nematode stylet puncturing the cell wall, and is followed by the secretion of enzymes and nutrient extraction. This process leaves cells that are damaged or completely destroyed.

Nematode damage can result in a variety of symptoms: 1. Lesions 2. Galls or swellings 3. Stunted plants 4. Loss of vigor 5. Excessive root branching 6. Twisted or distorted stems and/or leaves 7. Disruption in flower development / sterility 8. Dead or incapacitated root tips Disease Complexes - While nematodes are devastating pathogens, their most significant influence in agriculture results from their participation in pathogen complexes.

Damage

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

• Trichodorus spp. - Stubby-root nematodes • Netuviruses (NETU) rod-shaped - tobacco rattle virus, pea early browning virus • Xiphenema spp. – Dagger nematodes • Nepoviruses (NEPO) have a polyhedral shape grapevine fanleaf virus, tomato ringspot virus

Damage

Damage

Taxonomy

Kingdom Animalia Phylum Nemata Class Secernentea 5 other orders contain free-living forms and parasites of animals Order Aphelenchida - parasites of higher plants (usually on above ground parts), fungi, and insects Important genera:

Aphelenchoides

- foliar nematode

Bersaphelenchus

- pine wilt nematode Order Tylenchida - parasites of higher plants, insects, and fungi – largest % of plant pathogens Important genera:

Heterodera

spp. - cyst nematodes

Meloidogyne

spp. - root-knot nematodes

Pratylenchus

spp. - root-lesion nematodes

Taxonomy

Kingdom Animalia Phylum Nemata Class Adenophorea (as opposed to Secernentea) 11 other orders contain free-living forms and parasites of animals and microorganisms Order Dorylaimida - plant parasites/virus vectors (Stylet without knobs and no distinct median bulb) Important genera:

Xiphinema Longidorus Trichodorus

spp.- dagger nematode spp.- needle nematode spp.- stubby-root nematode

Root lesion nematodes

 Pratylenchus spp.

    7 important species in United States Most plants are susceptible to one or more species Migratory endoparasite, can leave and reenter the roots many times in its lifecycle. Males may or may not participate in reproduction.

Root lesion nematodes



Root-knot nematode

Meloidogyne spp.  M. incognita – southern-root knot   M. hapla – northern root-knot All are sedentary, endoparasites  After J2 stage enters the root and establishes giant cells (cells enlarge and rapidly divide) creating a more efficient nutrient sink for the nematode = gall production.

 After the J2 becomes an adult, males leave the root. The female will swell upon maturity producing several hundred eggs. Males may or may not participate in reproduction.

 Population is managed by the ratio of females : males that are produced. Immature females can change to males if the population density can not be supported.

Root-knot nematode

Juveniles in root

Root-knot nematode

Male, hatching from cuticle Gall, with female protruding Giant cell

Root-knot nematode

Root-knot Nematode

 Heterodera spp.

Cyst nematodes

 H. schactii – sugar beet cyst nematode   H. glycines – soybean cyst nematode – $3 billion in damage/year All are sedentary, endoparasites  After J2 stage enters the root and establishes a smaller feeding site than root-knot nematode. No gall production.  After the J2 becomes an adult, males leave the root to fertilize the females that have protruded through the root.  The female will swell upon maturity producing several hundred eggs outside and inside of her body. When she dies (4 wks old) her body will become a protective cyst for her young.  Some eggs will hatch immediately, some later in the season, next year or years, or never.

Soybean cyst nematode

Soybean cyst nematode

No visible symptoms with 30% yield loss Visible symptoms with 60 -80% yield loss

Dagger nematodes

 Xiphinema spp.

     3 important species in United States Characterized by long body and stylet.

Sedentary ectoparasite. Feeds only at the root tips. Feeding produces knobby, stunted roots. Males are required for reproduction, females produce very few eggs, but lives several months (most other nematodes live a few weeks).

Dagger nematodes

Dagger nematodes

Stubby roots Stunted plants

Dagger nematodes

(grape fan leaf virus)

Management Strategies

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

a. Crop rotation b. Trap crops c. Fallow e. Flooding or heat f. Tillage g. Planting date

Management Strategies

II. Breeding for resistance The use of nematode resistant varieties is a major management strategy. In many crops, chemical control is not economically viable and breeding is the only available tactic.

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

Management Strategies

III. Biocontrol The use of fungi, bacteria, viruses, other nematodes,to manage nematodes. The are many examples of biocontrol of nematodes, however, very few work in the field. Bacterium - endospore forming Pasteuria penetrans Fungus - adhesive rings by Arthrobotrys spp.

Management Strategies

IV. Chemical control The use of pesticides or other chemicals to reduce or eliminate nematode populations.

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

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