Mesocriconema xenoplax

Mesocriconema xenoplax is a plant pathogenic nematode. Nematodes of this particular species are collectively called ring nematodes.

Hosts and Symptoms

It has a wide host range, infecting many woody plants, and it is known to infect all species of the genus Prunus, which includes peach, almond, apricot, cherry, and plum. It also infects various other fruit trees, and grapes, in particular.

Symptoms can include, but are not limited to: root-pruning, decreased nutrient uptake, vascular damage, possible death of shoots and limbs, and stunted plant growth. With the reduced nutrient uptake, some cases have shown that the change in ratio if carbon:nitrogen can make plants infected by ring nematodes more susceptible to bacterial canker cause by Pseudomonas syringae, (Lownsberry, et al. 1977).

Anatomy and Morphology

Ring nematodes are easily distinguished by distinctive coarse ridges, known as annulations, around the body.

Females have a long, wide stylet, and have "knobs" that allow for the attachment of the stylet muscles. Head is broad, and the lip region shape is variable and sometimes there are four extra submedial lobes. The tail is broadly round, and the terminus is most often a small, simple, rounded button. The vulva is very distinctly open, and appears more posterior than usual.

Male ring nematodes tend to be much thinner than females, and they lack a stylet. They also lack a distinct esophagus, which renders them incapable of feeding. Their spicules are simple and slender, and can be straight or slightly curved.

Juveniles are much smaller than the adults, but tend to resemble adult females more than adult males.

Life Cycle

Ring nematodes live their lives as migratory ectoparasites. This means that they do not enter the plant cell, but instead use their large stylet to feed on the root tips from outside the plant. The nematode moves through the soil, and finds a root to feed on. It inserts its stylet into an epidermal cell on the plant, feeds for a certain amount of time, then moves along to a different locations, and feeds on a different root.

General Life Cycle for Mesocriconema xenoplax and Migratory Ectoparasites:

1. Adult females deposit single eggs in the soil, every two to four days.

2. First molt occurs within the egg, taking a first stage juvenile (J1) to a second stage juvenile (J2).

3. Second stage juveniles (J2) hatch from the egg in 11–15 days.

4. Second stage juveniles (J2) molt to third stage juveniles (J3) in three to five days.

5. Third stage juveniles (J3) molt to fourth stage juveniles (J4) in four to seven days, then become adults five to six days later.

6. Adult females begin to lay eggs in two to three days. Males rarely observed.

Environment and Distribution

Ring nematodes has a very broad distribution range. It has been reported in six of the seven continents: North and South America, Europe, Africa, Australia, and Asia—most notably India and Japan. In the United States, it is especially prevalent in California, and on the west coast.

Being a migratory ectoparasite, Mesocriconema xenoplax spends its life in the soil. It can be found in many different types of soil, including: highly porous soils, some silt and clay soils, and especially very sandy soils. It can be sensitive to dehydration, so soils that contain more moisture create the best environment.

See also

• List of almond diseases
• List of apricot diseases
• List of pecan diseases
• List of peach and nectarine diseases
• List of Persian walnut diseases
• List of grape diseases

References

External links

• Nemaplex, University of California - Mesocriconema xenoplax