Ditylenchus dipsaci

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symptoms of Ditylenchus dipsaci infestation on Narcissus bulb (click on image to enlarge it)
Source: Central Science Laboratory, Harpenden Archive, U.K. - IPM Images

Ditylenchus dipsaci (Kühn, 1857) - (stem and bulb nematode)

The nematode is wide-spread, mainly in temperate regions, and has many host plants, including onions, beans, other vegetables, cereals, potatoes and ornamentals. The nematode is a migratory endoparasite which means, it's location in the host plant is not fixed but it moves through the tissue. Plant parts attacked are stems, leaves, bulbs and tubers. Infections start with the nematode entering the plant through a stoma. It feeds on the content of cells through its stylet. This causes surrounding cells to divide and results in deformed leaves, stunted and swollen stems. Necrosis and rotting of plant parts is also a part of the disease because bacteria and fungi enter the damaged tissue. Yield losses can exceed 50% on a crop like onions.

The development cycle lasts 1-3 weeks, depending on the temperature and the host plant. Rapid population growth can result in severe crop damage, even when the initial population density is low.

Vernacular names
• Deutsch: Stengelälchen
• English: stem and bulb nematode
bloat nematode
alfalfa stem nematode
• Español: anguilula del tallo
• Français: anguillule des céréales et des bulbes
anguillule des tiges et des bulbes

The adult is about 1 mm long. It leaves the plant under moist conditions and can then infect other plants. In addition, the J4 stage survive severe desiccation for more than 20 years. This facilitates dispersal in seeds and bulbs, plant debris or contaminated equipment, and also by wind. Management options include healthy planting materials and seeds, heat treatment, crop rotation and fumigation.

About 30 host races with limited host ranges are known. Some of these "races" have been described as separate species, like Ditylenchus gigas.

For details see the respective page in Wikipedia.