Heterodera schachtii (Beet cyst eelworm, Sugarbeet nematode) is a plant pathogenic nematode. It infects more than 200 different plants including economically important crops such as sugar beets, cabbage, broccoli, and radish. H. schachtii is found worldwide. Affected plants are marked by stunted growth, wilting, yellowing, decreased yields, and death. While there are many methods of control, crop rotation with non-susceptible plants is preferred.

Discovery

In the early 1800s, "beet fatigue" was used to describe the decreased sugar beet yields which occurred after repeated planting on the same field. At first, this decrease was believed to be the result of nutrient depletion, but in 1859 the botanist H. Schacht discovered nematode cysts on the roots of affected plants and hypothesized that they were responsible for the disease. It wasn't until 1871 that another researcher, Schmidt, created the genus Heterodera, and named the nematode H. schachtii in honor of its discoverer .

Stage 1&2

Chemicals released from a susceptible host plant’s roots stimulate larvae to exit cysts which are located freely in the soil. Upon exiting the cysts, these larvae move toward the plant's root.

Stage 3

The larvae penetrate the root and release chemicals causing the plant’s cells to enlarge and extrude nutrients.

Stage 4

Both sexes burst through the root wall while their heads remain attached to the interior feeder cells. Males grow primarily in length while females swell to a lemon-like shape.

Stage 6

The fertilized mother continues to feed as her eggs develop. The mother eventually dies and her body toughens and becomes a cyst. The 400-500 eggs of the cyst remain sessile until stimulated by plant chemicals (at which point Stage 1 repeats).

Economic Impact

Because H. schachtii decreases crop yields globally, it has a significant economic impact on the agricultural industry. In 1999, H. schachtii was estimated to have cost European countries $90 million in losses for sugar beets alone. A small concentration of nematode can have a significant effect on crop yields. With just 18 eggs/gm of soil, yields of cabbage decreases by 28% . When there are more than 50 eggs/ml of soil, it is unprofitable to grow sugar beets and a crop loss of 5% is expected .

Identification

Stunted growth and yellowing are early signs of the disease. Infection can be confirmed by the presence of maturing cysts on plants’ roots.

Fumigants

Ethylene dibromide and metham-sodium are effective at controlling the nematode, but economic and environmental concerns generally prevent the use of fumigants as a form of control.

Soil Suppressiveness

H. schachtii is susceptible to infection by Verticillium suchlasporium and other fungi. When sugar beets are grown on a virgin field and a given amount of H. schachtii is introduced, beets are most vulnerable during the first several seasons. With the continued presence of the nematode in a field, infectious fungi levels rise, nematode concentrations decrease, and crop production increases . Experiments have attempted to control H. schachtii with fungi, but this method is not as economical as crop rotation.

Crop rotation

Eggs can survive within cysts for 10 or more years. However, ~40% of surviving eggs in a sessile cyst die each year. By growing non-susceptible plants for 2 or 3 years between sugar beet planting, nematode levels can be dramatically reduced. This is the primary method of control used commercially .