Characterization, Distribution and Fungicide Efficacy of Fusarium equiseti Causing Soybean Root Rot in Northeast China

Soybean root rot, a destructive soilborne disease complex caused by a consortium of pathogenic fungi, poses a persistent threat to global soybean productivity. During 2022–2023, a total of 990 fungal isolates were recovered from symptomatic soybean roots across Heilongjiang Province, Northeast China. Of these, 279 isolates were identified as Fusarium equiseti through integrated morphological characterization and multilocus phylogenetic analysis. Notably, F. equiseti exhibited markedly elevated isolation frequencies (5.6–58.9%) across surveyed regions, confirming its status as the emerging dominant causal agent of root rot in this agroecological zone. Pathogenicity evaluations revealed that 76.67% of isolates displayed moderate virulence, with one strain classified as highly virulent (3.33%). In vitro fungicide sensitivity assays indicated that F. equiseti was most susceptible to prochloraz (mean EC50 = 0.0010 µg·mL−1) and fludioxonil (mean EC50 = 0.0042 µg·mL−1). When deployed as seed treatments, these two fungicides achieved 53.61% and 47.32% control efficacy against root rot, respectively, while significantly enhancing soybean seedling emergence, root length, and fresh weight. Collectively, these findings provide a scientific foundation for the precise, sustainable management of F. equiseti-mediated root rot in cold-region soybean production systems.