**4. Biology and life cycle**

462 Soybean Physiology and Biochemistry

their seeds from all sorts of channels, and productions are in large scales. The climate change, especially the global warming caused by human activities is inevitably impacting

When the SCN was discovered, it was believed as a race of *Heterodera schachtii,* the sugar beet cyst nematode, since these 2 species are closely related biologically. Around that time, cyst nematodes were generally considered races of *H. schachtii*. In 1940 Franklin's comparative morphological studies led to many "races" being elevated to species. It was morphologically consistent that the morphological distinctions of the SCN led Ichinohe to

*H. glycines* is a typical cyst forming nematode within the family of Heteroderidae: characterized by sexual dimorphism: male is vermiform, while female lemon shaped (Figure 1). The brown cyst is the dead female with viable eggs inside. The second stage juvenile (J2) is vermiform, much smaller than the male. The length of the stylet, and the hyaline tail terminus of J2, and the characters of the vulva cone of the cyst are the most important characters for the identification (Table 1). More than one reference descriptions are usually required for comparison because there are variance among isolates from different crops and locations (Mulvey & Golden 1983, Wouts 1985, Golden 1986, Burrows & Stone 1985, Tylor

Fig. 1. Morphology of *Heteridera glycines*: A: male; B: J2; C: head of J2; D: cyst; E: hyaline tail

the soybean production, and the soybean cyst nematode.

**2. Taxonomic position** 

Phylum Nematoda, Class Secernentea, Order Tylenchida,

terminus

elevate the race to a new species in 1952.

Suborder Hoplolaimina,

**3. Morphology and identification** 

1975, Hesling 1978, Graney & Miller 1986).

 Superfamily Hoplolaimoidea, Family Heteroderidae, Genus *Heterodera*,

Species *Heterodera glycines* (Ichinohe 1952)

After the death of the female, the eggs are retained inside the hardened body (cyst), until suitable conditions arrive. The cysts can remain viable for several years in the soil. The eggs hatch to juveniles at stage 2, stimulated by exudates from the roots (Masamune et al., 1982). The 2nd stage juveniles (J2) of *H. glycines* are the only stage that the nematode can penetrate the root near the tip. The J2 once inside the root, become sedentary and establish a syncytic feeding site (Moore, 1984). J2 swells, and moults to J3, J4, and become adults (Wyss and Zunke, 1992). The life cycle is usually from 21 to 24 days (Fig. 2). Time required for the nematode to complete its life cycle is usually from 20-25 days at 20-24 0C, the lower the temperature is, the longer the time it takes to finish its life cycle (Melton et al., 1986).

Fig. 2. Life cycle of *Heterodera glycines* (courtesy of Dirk Charlson, Iowa State University)
