Suppression of the soybean cyst nematode, Heterodera glycines, using water extract of bean sprout residue

The soybean cyst nematode (SCN),Heterodera glycines, is a widespread pest in most soybean-producing areas, causing serious damage to soybean crops and resulting in economic losses. We have previously reported that bean sprout residue might function as an environmentally-friendly control agent against SCN. In order to understand the role of water extracted from bean sprout residue as a possible factor in lowering the number of SCN, either water extract of bean sprout residue (WE) or water (W) was applied to pots containing soil infested with SCN, and komatsuna plants, a leafy vegetable, were grown in these pots. After 2 months, the number of SCN, estimated with real-time PCR, was 80% lower in WE than in W and the biomass of komatsuna plants was 100% higher in WE than in W, suggesting that WE has not only an SCN eradication effect but also a fertilisation effect. In field experiments, WE or W was applied ten times during the experimental period from July 2010 to June 2011. The number of SCN decreased by 82% in WE and by 36% in W; however, the marked decrease was observed only between July and September and between April and June. Green soybean plants were grown in the field where WE or W had been applied and the yield was markedly higher in WE (750 g m−2) than in W (200 g m−2). The hatching stimulation of SCN eggs by WE was tested at four different temperatures (10, 20, 25, 30°C) and was observed only at 25°C. These results show that water extract of bean sprout residue decreases the density of SCN and thereby damage to green soybeans, and that the suppressive effect depends on soil temperature.