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Nematodes Introduction - kingdom: Animalia - feed on microorganisms and microscopic plants and animals - obtain food with stylets - cause billions of dollars damage annually Characteristics - small and invisible to the naked eye - smooth unsegmented bodies Anatomy - transparent - lips (6) around mouth - hollow stylet - reproduction in plant parasitic nematodes is through eggs and may be sexual or parthogenic - many species lack males Life Cycles - have four juvenile stages Ecology and Spread - soil temp., moisture, and aeration affect survival and movement of nematodes in the soil - most eggs hatch freely in water in the absence of any special stimulus - 2 genera Classification - belong to phylum Nematoda - 2 orders - ectoparasites: feed only from the outside on the cells near the root surfaces - endoparasites: enter the host and feed from within - migratory: live freely in the soil - sedentary: do not move about Symptoms Caused by Nematodes - appearance of symptoms on roots as well as on the aboveground parts of plants - root knots or root galls, root lesions, excessive root branching, injured root tips, and root rots - yellowing of foliage, excessive wilting in hot or dry weather, reduced yields, and poor quality of products - aboveground galls, necrotic lesions and rots, abnormal development can occur How Nematodes Affect Plants - direct mechanical injury - secretion of saliva injected into plants - puncturing of cell wall, inject saliva into the cell, withdraw part of the cell contents - cause tissue disentegration and the death of cells - cause cell enlargement in some cases Interrelationships between nematodes and other plant pathogens - etiological complex resulting in a combined pathogenic potential that can be greater than the individual damages that can be done by just the pathogen or just the nematode - nematodes lower the natural resistance to the fungus Control of Nematodes - crop rotation - biological control with resistant varieties - physical agents, such as heat and flooding - control with chemicals like nematicides Root-Knot Nematodes (Meloidogyne) - favor warm or hot climates and short or mild winters - damage plants by devitalizing root tips and causing formation of swellings of the roots Symptoms - aboveground symptoms are reduced growth and fewer, small, pale green, or yellowish leaves that tend to wilt in warm weather - underground infected roots swell and develop into root-knot galls The Pathogen - second-stage juvenile is the only infective stage of the nematode - the juvenile enters the root where it inserts its stylet and secretes saliva into the cells - the juvenile turns into a female and produces eggs with or without the male’s help - when the eggs hatch, second-stage juveniles cause new infections in the same root Development of Disease - Giant cells are formed (3-6) Control - control in greenhouses with steam sterilization of the soil or soil fumigation with nematicides - resistant varieties Cyst Nematodes: Heterodera and Globodera - known as the “golden nematode” - severe in potato, tomato, and eggplant - diagnostic feature is the presence of cysts on the roots and usually the proliferation of roots and production of shallow, bushy root systems - enlarged cells are known as syncytia Lesion Nematodes: Pratylenchus - attack the roots of all kinds of plants such as cereals and other field crops, vegetables, fruit trees, and ornamentals - form local lesions on young roots, which may then rot because of secondary fungi and bacteria Symptoms - plants appear stunted and chlorotic as though they are suffering from mineral deficiencies or drought - yields are reduced drastically - can kill plant - infected roots at first show small, water-soaked lesions that soon turn brown to almost black The Pathogen: Pratylenchus - nematodes overwinter in infected roots or in soil except for egg-producing females, which cannot survive in the winter Control - row treatment of the soil with nematicides before the crop is planted
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