Soybean Cyst Nematode, Heterodera glycines
The soybean cyst nematode (Heterodera glycines) is a parasitic worm that infects soybean plants, and other legumes, across the world. It is thought to be native to Asia, but was found in the United States in 1954 and in Colombia in the 1980’s. It can be found in Italy and Iran and its most recent sightings have occurred in Brazil and Argentina, two major areas where soybeans are grown. These worms are highly damaging to American soybean crops, costing the industry as much as 500 thousand dollars a year.
The soybean cyst worm infects root systems in its second stage, traveling through the plant cells to the vascular tissue. In this area of the plant, the worm is able to cause cell division within the plant itself to create feeding sites throughout the area. This species grows quickly as it feeds, with females growing so large that their back ends penetrate the plant and can be seen from the outside. Males, however, do not grow out of the plant, retaining their worm shape and moving from plant to plant to fertilize the female’s eggs. Females will feed on the plant, laying between 200 and 400 eggs in one sac during her lifetime. After the female dies, her body forms a hard cuticle that protects the sac and the eggs inside of it. The eggs will most likely hatch if they reside in favorable soil conditions, producing stage two larvae that will continue the species. Typically, there are three generations of this worm each year, but in inadequate conditions, a cyst may survive for many years until hatching conditions are better.
The symptoms of a soybean cyst nematode infection are not unique to that type of infection, so diagnosis can be difficult. These symptoms include those that can be caused by nutrient or iron deficiency, damage from herbicides, drought stress, or other plant diseases. Although stunted growth of the plant and yellowing leaves can show a possible infection, the only efficient way of confirming an infection is to look for cysts or female worms within the root systems.
It is possible to restrict the movements of the soybean cyst nematode by using resistant cultivars and crop rotating practices. Crop rotating is especially effective, because the worm must have a living, legume host to live in. By planting a crop that does not support the worm in an area where the eggs are present, it is possible to reduce the spread of the parasite. In areas where crops cannot be rotated, but where worms are not yet a problem, proper plant and soil nutrition is vital in controlling the effects of the worm.
Image Caption: Low-temperature scanning electron micrograph of soybean cyst nematode and its egg. Magnified 1,000 times. Credit: Wikipedia