''Heterodera medicaginis'', the alfalfa cyst nematode, is a plant pathogenic nematode which is cited as an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

. It is closely allied to '' Heterodera daverti'', '' H. glycines'' and '' H. sonchophila'' in the H. schachtii-group. The only known host plant of this obligate parasite is the important crop alfalfa or lucerne, ''

Medicago sativa Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, and silage, as we ...

''.A Redescription of Heterodera Medicaginis
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Description

The female alfalfa cyst nematode is white and shaped like a lemon with a body length of 0.4 to 1.2 mm and a width of 0.2 to 0.9 mm. The male is

vermiform Vermiform (ˈvərməˌfôrm) describes something shaped like a worm. The expression is often employed in biology and anatomy to describe usually soft body parts or animals that are more or less tubular or cylindrical. The word root is Latin, ''ve ...

with a body length of 1.2 to 1.4 mm and a width of about 0.028 mm. The

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

are

reniform Reniform is an adjective meaning "kidney-shaped" and may specifically refer to: * Reniform leaf The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single ...

, measuring 0.12 by 0.05 mm and the first two

instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e are vermiform. The second instar larvae are mobile in damp soil and search down to a depth of 30 centimetres for suitable roots to invade. Here they develop further and become sedentary, burying their heads in cells and feeding on the cell sap. The central part of their bodies swells, and after moulting they develop into bottle-shaped third instar larvae and after moulting again, lemon-shaped fourth instar larvae. The swollen larvae break out of the root cortex. At this stage they differentiate into males and females. The males become mobile and migrate through the soil searching for females with which to mate. The females remain attached to the root tissues by their heads, continue feeding and start laying eggs. These are held within the bodies of the females which later die and turn into brown cysts with hard cuticles. These eventually become detached from the roots. The eggs develop into larvae inside the cyst and some second instar larvae emerge into the soil to start a new cycle of development. Most of the larvae lie in a state of anabiosis within the cysts where they can remain dormant for several years and still be viable.AgroAtlas
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Economic significance

The alfalfa cyst nematode causes a decrease in yield of herbage and seeds. The main criterion is the population density of larvae in spring. A 5-10% threshold of harmfulness occurs when there are 330 to 890 larvae per 100 cubic centimetres of soil. Control measures preventing yield losses include crop rotation and the use of tolerant varieties. Other factors affecting the harm done include the date of sowing, the density of seeding, the use of cover crops and the weather.

References

{{Taxonbar, from=Q5747107 medicaginis Plant pathogenic nematodes Nematodes described in 1971