2 Nematode DamageRarely, 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.
3 Nematode DamageQuite 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.
4 DamageMechanical 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. Lesions2. Galls or swellings 3. Stunted plants4. Loss of vigor5. Excessive root branching 6. Twisted or distorted stems and/or leaves 7. Disruption in flower development / sterility 8. Dead or incapacitated root tipsDisease Complexes - While nematodes are devastating pathogens, their most significant influence in agriculture results from their participation in pathogen complexes.
5 DamageNematodes 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 nematodesNetuviruses (NETU) rod-shaped - tobacco rattle virus, pea early browning virusXiphenema spp. – Dagger nematodesNepoviruses (NEPO) have a polyhedral shape - grapevine fanleaf virus, tomato ringspot virus
8 Taxonomy Kingdom Animalia Phylum Nemata Class Secernentea 5 other orders contain free-living forms and parasites of animalsOrder Aphelenchida - parasites of higher plants (usually on above ground parts), fungi, and insectsImportant genera:Aphelenchoides - foliar nematodeBersaphelenchus - pine wilt nematodeOrder Tylenchida - parasites of higher plants, insects, and fungi – largest % of plant pathogensHeterodera spp. - cyst nematodesMeloidogyne spp. - root-knot nematodesPratylenchus spp. - root-lesion nematodes
9 Taxonomy Kingdom Animalia Phylum Nemata Class Adenophorea (as opposed to Secernentea)11 other orders contain free-living forms and parasites of animals and microorganismsOrder Dorylaimida - plant parasites/virus vectors(Stylet without knobs and no distinct median bulb)Important genera:Xiphinema spp.- dagger nematode Longidorus spp.- needle nematode Trichodorus spp.- stubby-root nematode
10 Root lesion nematodes Pratylenchus spp. 7 important species in United StatesMost plants are susceptible to one or more speciesMigratory endoparasite, can leave and reenter the roots many times in its lifecycle.Males may or may not participate in reproduction.
12 Root-knot nematode Meloidogyne spp. M. incognita – southern-root knot M. hapla – northern root-knotAll are sedentary, endoparasitesAfter 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.
17 Cyst nematodes Heterodera spp. H. schactii – sugar beet cyst nematode H. glycines – soybean cyst nematode – $3 billion in damage/yearAll are sedentary, endoparasitesAfter 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.
19 Soybean cyst nematode No visible symptoms with 30% yield loss
20 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).
24 Management Strategies I. Cultural practices - Includes agricultural tactics that indirectly influence pathogen populations and communities.a. Crop rotationb. Trap cropsc. Fallowe. Flooding or heatf. Tillageg. Planting date
25 Management Strategies II. Breeding for resistanceThe 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.
26 Management Strategies III. BiocontrolThe 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 penetransFungus - adhesive rings by Arthrobotrys spp.
27 Management Strategies IV. Chemical controlThe 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