First Report of Celery Stem Base Rot Caused by <i>Fusarium sporotrichioides</i> in Ningxia, China

Celery (Apium gravedens L. var. dulce) is a main vegetable crop in the Ningxia Hui Autonomous Region of China. A new stem base rot of celery was observed in many celery fields in Xiaohe Township, Xiji County, Ningxia during 2023-2025. The average disease incidence of the celery was 10%–15%. The tissue at the base of celery stems was observed to turn brown to black, followed by dehydration and shrinkage (Fig. 1). Stem tissues of diseased celery plants were chopped into small pieces, sterilized with 75% ethanol for 30 s, disinfected in 5% sodium hypochlorite for 1.5 minutes, rinsed three times in sterile water, and then plated on potato dextrose agar (PDA) medium, followed by incubation for 7 days at 25°C in the dark. A total of 12 isolates were recovered and purified by the single spore culture method. These isolates were inoculated on celery for pathogenicity testing. Two isolates (named ZF4 and ZF5) were observed to cause diseases. The colonies of ZF4 and ZF5, grown on PDA at 27°C in the dark for 10 days, produced fluffy, white aerial mycelium and purple to deep brick-red pigment. On carnation leaf agar (CLA), microconidia were abundant, measuring 4.98–15.75 × 2.49–3.90 µm (n=30), with pyriform, oval, and fusiform shapes, and 0-1 septate. Macroconidia were insufficient, measuring 18.04-38.72 × 3.51-5.27 µm (n=30), with fusiform or sickle-shaped, and 2-4 septate. Sporodochium and phialide morphology were observed on PDA, and spherical chlamydospores on synthetic nutrient agar (SNA) (Leslie and Summerell 2006) (Fig. 2). Molecular identification was performed by parial sequences of the translation elongation factor 1-α (TEF-1α) (O’Donnell et al. 1998) and RNA polymerase II (RPB2) (O’Donnell et al. 2007) genes. The sequences were used to perform maximum likelihood analysis with TEF-1α and RPB2 from species of the Fusarium genus. Phylogenetic analysis indicated that the isolates of ZF4 and ZF5 were clustered with five isolates of Fusarium sporotrichioides in GenBank, and their TEF1-α and RPB2 sequences revealed 99% similarity to those of the five isolates (Fig. 3). The consensus sequences from the two isolates were deposited in GenBank (accession numbers: PV855386 and PV870247 for TEF-1α, respectively; PV855387 and PV870248 for RPB2, respectively). Pathogenicity was tested in the field with temperatures of 18°C-27°C. Spore suspensions (106 spores/ml) were sprayed onto the stem base of 40-day-old celery plants. Sterile distilled water was used as a negative control. This trial was replicated three times. Atrophied dark brown lesions on the stem base were observed 10 days after inoculation, accompanied by a certain degree of rot (Fig. 1). Inoculated celery plants showed symptoms, similar to those from field infections. Control plants were symptomless. The pathogen was reisolated from symptomatic plants and identified as Fusarium sporotrichioides based on morphological characteristics and sequencing of the TEF-1α and RPB2 genes. To our knowledge, this is the first report of celery stem base rot caused by Fusarium sporotrichioides.