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Significance

The first documented report of damage by the soybean cyst nematode (Heterodera glycines Ichinohe) was by S. Hori in Japan in 1915. Ancient Chinese literature and personal communications, however, suggest that SCN may have been a pathogen of soybean in China as early as 235 B.C. The term "soybean yellow dwarf" was adopted by Japanese researchers in the 1920s to describe the pale yellow areas of poor soybean growth observed in fields.

SCN was first reported in the United States in 1954 in Hanover County, North Carolina – an area known to import flower bulbs from Japan. The rapid spread of SCN to other soybean-growing states has prompted some hypotheses that the nematode is indigenous and parasitizing some leguminous weeds in the U.S. However, there are indications that soybean seed had been imported to the United States as early as 1765. More significant may be the importation of soil from Asia in the late 1800's to obtain inoculum of Bradyrhizobium japonicum for nitrogen fixation in soybean. Some imported soil was distributed among researchers who were working on the improvement of soybean cultivation in the U.S. Soil also was shared among growers to obtain nitrogen-fixing inoculum once its utility had been demonstrated.

The rapid expansion in production acreage of soybean in the U.S. that started in the mid-1900s served to establish a huge reservoir of host crop for the increase of SCN. A federal quarantine for SCN was established in 1957, but the quarantine was lifted in 1972 because it was ineffective. It has been suggested that the movement of SCN-infested soil and plant material into new soybean production areas had already occurred before the quarantine could be established. SCN now infests every soybean-producing state in the U.S. (Figure 22), with total soybean yield loss estimates approaching $1 billion per year! Though SCN has been a recognized pathogen of soybean in the southeastern United States since the 1950s, the detection and effects of SCN in the midwestern U.S. "soybean belt" has been more recently realized.

Figure 22

SCN was detected in Colombia, South America, in the early 1980s, and was soon thereafter found in Argentina and Brazil - two of the world's important soybean production areas. More recently, SCN was reported from Italy, and if soybean production is expanded in Europe, more SCN infestations will likely be found. In a recent survey of the top ten soybean- producing countries in the world, SCN was found to be the most damaging pathogen of soybean.

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