Ditylenchus dipsaci
| Stem and bulb nematode | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Nematoda |
| Class: | Tylenchoidea |
| Subclass: | Diplogasteria |
| Order: | Tylenchida |
| Superfamily: | Tylenchoidea |
| Family: | Anguinidae |
| Subfamily: | Anguininae |
| Genus: | Ditylenchus |
| Species: | D. dipsaci |
| Binomial name | |
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Ditylenchus dipsaci (Kuhn, 1857) |
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| Synonyms | |
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Ditylenchus dipsaci is an plant pathogenic nematode that primarily infects onion and garlic. It is commonly known as the stem nematode, the stem and bulb eelworm, or onion bloat (in the United Kingdom). Symptoms of infection include stunted growth, discoloration of bulbs, and swollen stems. D. dipsaci is a migratory endoparasite that has a five-stage lifecycle and the ability to enter into a dormancy stage. D. dipsaci enters through stomata or plant wounds and creates galls or malformations in plant growth. This allows for the entrance of secondary pathogens such as fungi and bacteria. Management of disease is maintained through seed sanitation, heat treatment, crop rotation, and fumigation of fields. D. dipsaci is economically detrimental because infected crops are unmarketable.
D. dipsaci is a microscopic worm about 1.5 mm long. It penetrates into plants from either the soil or infested planting material and occasionally from seeds. They live between the cells of onion or garlic leaves and between the scales of the bulbs where they feed on cell sap and multiply. The female lays 250 eggs during a season and six generations may develop under optimum conditions when the temperature is in the range 15–20 °C. As the number of nematodes increase, symptoms become visible. Onion leaves start to curl, garlic leaves become yellow and die, bulb scales are loosened, and bulb necks become cracked. Development continues in infested bulbs during storage. D. dipsaci is not restricted to onions and garlic. Its other plant hosts include peas, beetroot, vegetable marrow, pumpkin, rhubarb, and ornamental bulbs. Some weeds also act as hosts, including Stellaria media, Linaria vulgaris, Polygonum aviculare, Fallopia convolvulus, and Galium aparine.
Stem and bulb nematodes are migratory endoparasites. Their lifecycle occurs in five stages with the first molt occurring in the egg and the second and third molt occurring in the soil. By the fourth stage, juveniles have entered the plant through young tissue and/or seedlings. The fourth molt then occurs inside the plant. The adult female must mate with a male to reproduce and lay eggs. A complete reproductive lifecycle of the stem and bulb nematode is 19–25 days (egg to egg). Reproduction takes place in succulent, rapidly growing tissues or in storage organs and continues throughout. A female can lay 200–500 eggs in her lifespan. However, if conditions are unfavorable, the nematodes can halt their lifecycle. The lifespan of stem and bulb nematodes is about 70 days. Most generations are passed inside bulbs, stems and leaves. Eggs and larvae overwinter in dried infected host material. They are also found in weed hosts and seeds of composite. Stem and bulb nematodes can survive up to two years in freezing or extremely dry environments in the soil.D. dipsaci can survive on or in plant tissue by entering cryptobiosis and survive for 3–5 years in this stage. During dormancy, D. dipsaci shows no sign of life and the metabolic activity is almost at a standstill.
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Wikipedia