1. Section 4 Plant Parasitic Nematode

2. Brief introduction of plant nematodes  Nematodes - helminthes, are low invertebrate( 无脊 椎动物 ). They are the most abundant group of multicellular animals on earth, thriving in most habitats. E.g. Soil, freshwater and seawater. Most nematodes can parasitize human, animals and plants.  Nematodes which damage plants are entitled plant pathogenic nematodes or plant parasitic nematodes.

3.  Of the multitude of nematode species known, about 2500 species are able to feed on plants. Most attack roots and underground parts of plants (e.g. rhizomes, tubers). Some are able to feed on leaves and flowers. Nematodes are found in all climates and every type of soil, while every agricultural crop will host some species.  Plant parasitic nematodes obtain their nutrients exclusively from plants. They cannot feed on dead plant tissue and must have access to living plants if they are to complete their life cycles. While feeding, nematodes may damage plants and cause disease.

4. 1.Shape and structure of plant nematodes  Obvious difference in size, slenderly vermiform( 蠕虫形的） ; some adult female nematode, lemon-like or pyriform( 梨形 ), body wall transparent.  The body divides into four sections, i.e. head, neck, abdomen, tail; having body wall and body cavity; there are digestive system, reproductive system, etc in the body cavity.  There is a stylet which look like a miniature hypodermic needle in nematode’ mouth. A nematode feeds on a plant by puncturing （刺破） the cell wall with this stylet and sucking out the contents of the cell. Not only do nematodes suck out juices from plant cells, they also inject liquids into the cells and in this way may introduce viruses into plants.

5. 2. Life history of plant pathogenic nematodes  When the growing season begins, soil water carries substances exuded from plant roots to the dormant eggs causing them to hatch. From each egg a larva hatches which is capable of wriggling short distance in soil water. The newly hatched larvae attached to the plant roots, swim to the roots, enter, and proceed to feed and grow to adults. This usually take place in less than a month if the soil is warm and moist.  The new adults lay more eggs. Several generations of nematodes may appear during the growing season, constantly producing new nematodes to feed on the roots and drain( 消耗 ) away energy from the plant.

6. 3. Dispersal of plant nematodes  Nematodes spread very slowly by their own efforts. Most nematodes never move more than a few centimeters from the spot where they hatched. Nematodes can be spread by farming activities. Nematodes can be contaminants on the parts of plants: corms( 球茎）, rhizomes( 根茎）, roots, tubers, seeds, flowers, leaves, and stems. In the soil, nematodes stick to tools, vehicles, and the feet of animals. drainage and irrigation water also carry the eggs and larvae long distances to begin new centers of infection. In dry weather, strong winds may blow the eggs or nematodes from one field to another.

7. 4. Ecology of plant parasitic nematode  Nematodes are aquatic. Except larva, ovum, cyst in dormancy, nematodes need to live in water or to parasitize in alive cell and tissue.  Nematode can normally grow in 15-30 ℃, and can be killed in 40-50 ℃ for 10 minutes.  Mostly nematodes live in cultivation layer, especially in the soil around the roots.  In warm, damp soils, nematodes are very active, As the temperature cools, nematodes become less active. In warm climates, nematodes multiply at the rate of 5 to 10 generation a year and are also more vigorous in finding and attacking plants than in colder area.  Plant parasitic nematode are obligate parasites.

8. 5.1 Meloidogyne ( 根结线虫属）  Female nematode and male nematode have different shape. Female is pyriform with a obvious neck; male is linear. Endoparasites.  Eggs laid outside the female body in a gelatinous matrix sac( 卵囊） that often protrudes to the surface of the root and can be seen on the root surface as a sign ． 5. Main groups of plant pathogenic nematodes

9.  Forming “giant cells” or tumour in root.  Reproduction by parthenogenesis.( 孤雌生殖）  Parasitize in many species of plant, e.g. cyclamen( 仙客来 ) ， Chinese flowering crabapple( 四 季海棠 ) ， coxcomb( 鸡冠花 ) ， peony( 牡丹 ) ， Chinese rose ( 月季 ) ， willow( 柳树 ).

10. 5.2 Ditylenchus( 茎线虫属）  Female and male are linear; the tail is cuspate, the body length is 2mm, the female is tubbish ( 肥胖）．  Obligate endoparasites of higher and lower plants. Usually feeds below ground on tulips( 球茎 ) and other bulbs( 鳞茎 ).  Reproduction by amphimixis （两 性交配）.  Cause Swelling （隆起） and distortion to leaves, brown rings in bulbs.  Life cycle is 19-23 days at 15 ℃.

11. 5.3 Aphelenchoides( 滑刃线虫属）  Nematode is 0.5-1.2mm long, and slender ． They have a slender stylet with small, distinct knobs.  Endoparasite in leaves, but also feeds ectoparasitically on leaf and flower buds in some plants.  Nematode genus has wide host-range and is usually associated with leaves and buds.  Causing leaf shrinkage, russet lesion( 枯斑）, dead buds, stalk wilt, stalk rot.  They enter and leave the host plants by natural openings.

12. 5.4 Pratylenchus( 短体线虫属）  Adult nematodes are columnar( 圆桶 状）, the body length less than 1mm; Migratory endoparasite.  Pratylenchus does best in sandy soils ．  Bringing forth root lesion, stunting, chlorosis and discoloration of many plants, e.g. lily, narcissus( 水仙花 ), Chinese tulip tree( 鹅掌楸）．  Reproducing by parthenogenesis( 孤 雌生殖） or Sexual reproduction( 两性生 殖）.  Eggs laid singly in roots and soil; second stage hatches from egg.

13. 5.5 Bursaphelenchus( 伞滑刃线虫属）  Female and male nematodes are vermiculate( 蠕虫形的 ), body length 1.oomm ； tail is arcuate( 弓形）  Bringing forth wilt of pine, spruce( 云 杉 ), Larch( 落叶松 ). Affected trees can turn brown and die in as little as 3 weeks.  Transported by Pinesawyer beetles ． The nematodes spread throughout the tree and multiply very rapidly.