Yellowing symptoms sometimes cause yield losses in green soybean cultivation. The objective of this study was to estimate the yield loss factors in a glasshouse. The parameters evaluated were plant-parasitic nematodes (Heterodera glycines, Pratylenchus penetrans, Meloidogyne spp.) and soil chemical properties. While the density of H. glycines did not show a negative correlation with yield in the February planting date, it showed a strongly negative correlation in the March planting date. Multiple regression analysis showed that yield was significantly correlated with P. penetrans and nitrate in the February planting, and with H. glycines and K in the March planting. The present study revealed that yield loss was caused by P. penetrans and nitrate in seasons with unsuitable temperatures for H. glycines hatch, and by H. glycines and alleviated by K in seasons with optimum temperatures for H. glycines hatching.
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.
The effects of the application of bean sprout residue to soil on the soybean cyst nematode (SCN) Heterodera glycines were evaluated in pot experiments. When bean sprout residue was applied into a soil infested with SCN at a rate of 1%, the number of SCN second-stage juveniles (J2), measured with the Baermann method, increased after 14 days of application and then decreased markedly after 35 days, indicating that some J2 hatched in response to a stimulant in the bean sprout residue and then starved to death in the absence of a host. Next, bean sprout residue was applied two or four times and the number of SCN after 7 weeks was estimated with real-time PCR, which enables quantification of all the forms of SCN (eggs, J2, cysts). Results showed that the SCN density did not change in the untreated control, while it decreased by more than 70% in the residue treatment. Such a hatching-stimulatory and subsequent eradication effect was observed in the water extract of bean sprout residue. Among different parts of bean sprout, both of the stem and root parts had a higher stimulatory effect for hatching, while a stimulatory effect decreased in the stem part greened by culturing under light conditions. These results revealed that bean sprout residue might function as an environmental-friendly control measure for SCN.
We previously reported that incorporation of bean sprout residue into soil stimulated hatching of the soybean cyst nematode (SCN), Heterodera glycines. The objective of this study was to evaluate the effects of short-term growth of mung bean (Vigna radiata), the raw material of bean sprout, and its incorporation into the soil on the density of SCN in soil. When mung bean was grown in pots for 2 and 4 weeks in a SCN-infested andosol, incorporated into the soil and further incubated for 2 weeks, the SCN density decreased markedly. Mung bean was also grown in pots under different moisture conditions. The SCN density decreased in the soils with 48-68 g water, but not with 39 g water (100 g dry soil)−1 in which mung bean grew the poorest. The present study suggests that short-term growth of mung bean may be useful to decrease the density of SCN in soil.