Identification, Pathogenicity, and Chemical Control of <i>Nigrospora oryzae</i> , a New Pathogen Causing Mid-Late Soybean Root Rot in Heilongjiang, China

Soybean root rot, a soil-borne fungal disease, severely impacts soybean production. Limited research has specifically addressed this disease during the mid-to-late growth stages, which represent a critical yield-limiting period for soybean. In the autumn of 2024, a total of 478 pathogenic isolates were obtained and validated following Koch’s postulates. These isolates were classified into eight fungal species, among which Diaporthe longicolla was the predominant species, accounting for 72.0% of the total isolates. Notably, Nigrospora oryzae, an unreported causal agent of soybean root rot in China, was first isolated from field samples collected in Jiamusi City, constituting 2.1% of all obtained isolates. Pathogenicity assays revealed that most isolates exhibited high or moderate virulence. Host range assays confirmed that N. oryzae had a broad host spectrum, infecting green pea, snow pea, lentils, flower-faced cowpea, and mung bean, but not kidney beans, red beans, corn, or peanut. Fungicide sensitivity tests indicated N. oryzae was highly sensitive to difenoconazole and prochloraz, which exhibited excellent field control efficacies of 87.50% and 69.58%, respectively, with prochloraz being more suitable for field application. This study provides basic data for the integrated management of N. oryzae-induced soybean root rot via non-host crop rotation and prochloraz.