Evaluation of field soils for suppressing reproduction of soybean cyst nematode, Heterodera glycines, in North Dakota, USA

Summary Soybean cyst nematode (SCN: Heterodera glycines ) poses a significant threat to soybean production in many US states including North Dakota (ND). Common management strategies, such as using resistant cultivars, crop rotation and nematicides, have limitations. Suppressive soil is a soil that naturally prevents the establishment of a pathogen or inhibits its damage to the host plant, and it can be used as an alternative method for SCN management. This study aimed to assess field soils in ND for reducing SCN reproduction to identify the potential suppressive soil against SCN. In our previous observations, 23 soybean fields in ND showed a decreasing SCN population over the past years. Thus, these fields were sampled and SCN cysts were recorded. Of these, ten fields showed lower SCN densities and were further investigated for suppressiveness. Two experiments with four runs were conducted in a growth chamber at 27°C for 60 days, and then SCN white females, eggs, and juveniles were recorded. Among ten fields, Field 2 and Field 3 significantly suppressed SCN as evidenced by the significant reduction of SCN white females, final population densities and reproduction factors in the inoculated natural field soils compared to their inoculated autoclaved (conducive) field soils. None of the field soil significantly reduced SCN when 90% of autoclaved field soil was mixed with 10% natural field soil. However, when 50% of the natural field soil was mixed with 50% of the autoclaved soil, Field 2 was found to significantly reduce the SCN population in the soil mix. The results of this study suggested that Field 2 and Field 3 possessed different degrees of suppressive potential. Further examination of potential innate biocontrol agents in these soils may help explain the population dynamics of SCN and low SCN population densities in these fields.