Seed Treatment with Fluopyram Provides Effective Management of Soybean Cyst Nematode (Heterodera glycines) and Enhances Soybean Growth.

Soybean cyst nematode (SCN, Heterodera glycines) is one of the most yield-limiting nematodes in soybean production. Application of synthetic nematicides is a critical component in the integrated management of SCN in China. However, resistance has developed in SCN to conventional nematicides, leading to the failure of these nematicides in some fields. It is pivotal for the soybean industry to develop new nematicides that can achieve sustainable nematode control. Seed treatment is a promising control approach. Fluopyram is widely used to control various plant-parasitic nematodes; however, it is currently not registered as a seed treatment in China for use in controlling SCN. In this study, the efficacy of fluopyram as a seed treatment to manage SCN was evaluated through in vitro tests, greenhouse experiments, and field trials. In vitro tests showed that fluopyram caused a high mortality of H. glycines second-stage juveniles (J2s), with 50% lethal concentration (LC50) value of 0.96 mg/liter that was superior to abamectin. In greenhouse experiments, compared with the untreated control, seed treatment with fluopyram at 0.15 mg active ingredient (a.i.)/seed provided significant SCN control while maintaining excellent soybean root length and shoot fresh weight, better than the commercially available seed treatment with a 35.6% formulation of abamectin + carbendazim + thiram at 10 ml/kg seed. Moreover, in split-root experiments, fluopyram treatment at 0.15 mg a.i./seed reduced the number of J2s inside the roots by 65.3% and induced resistance to SCN. Fluopyram also enhanced activities of phenylalanine ammonia-lyase and peroxidase, which was associated with the increased expressions of the defense-related genes GmNPR1-1, GmSAMT1, and GmACS9b. In two consecutive years of field trials, fluopyram seed treatment at 0.15 mg a.i./seed exhibited significant control of SCN. Compared with the control, it reduced the numbers of cysts on the roots, cysts in the soil, and nematode juveniles inside the roots by 57.5, 52.2, and 63.6% in 2023 and 63.7, 57.2, and 67.9% in 2024, respectively. These results indicated that fluopyram not only exhibited strong nematicidal activity against H. glycines but also induced systemic resistance in soybean. In summary, fluopyram seed treatment has the potential to manage SCN in the field and warrants further studies.