Survey of soybean cyst nematode population abundance and virulence phenotypes in the Sanjiang Plain of Heilongjiang Province, China

Heilongjiang Province is China’s leading soybean-producing region, where the soybean cyst nematode (SCN; Heterodera glycines Ichinohe) has expanded across an increasing geographic range. Recent surveys reported SCN presence in at least 63 soybean-producing counties; however, eastern production zones remain insufficiently characterized. To evaluate the current distribution, population density, and virulence structure of SCN in the Sanjiang Plain, we collected 186 soil samples from 6 major soybean-producing counties in 2024. Samples represented four dominant soil types: black soil (Phaeozem), meadow soil, dark brown soil (Cambisol), and albic soil. SCN was detected in 93.5% of fields, confirming its widespread establishment. Cyst densities ranged from 2 to 10 cysts per 100 g dry soil, corresponding to 122–579 eggs and juveniles per 100 g soil. Population densities were lower under maize–soybean rotation (204 eggs and juveniles per 100 g soil) than under continuous soybean (252 per 100 g), though the difference was modest. Under continuous soybean cultivation, dark brown soils supported significantly higher densities (420 per 100 g of dry soil) compared with black and meadow soils, suggesting that soil type may strongly modulate SCN abundance within this cropping system. Virulence testing of nine representative populations classified all populations as race 3. Female index values remained below 10% on PI 88788, PI 90763, and Pickett, indicating no detectable shift toward broader virulence in this region. Collectively, these findings indicate that although SCN is widely distributed in the Sanjiang Plain, population pressure and virulence complexity remain moderate relative to western Heilongjiang. The dominance of race 3 suggests that current resistance sources remain effective, providing an opportunity for proactive resistance deployment and integrated management to prevent future virulence evolution in this expanding soybean production region.