First Report of Peanut Top Rot Caused by <i>Fusarium pernambucanum</i> in China

Peanut (Arachis hypogaea L.) is a major economic and oilseed crop in China, with an annual planting area maintained at roughly 350,000 hm2 in Guangdong. In April 2025, top rot were observed on peanut in Zhanjiang, Guangdong Province, with an incidence rate of about 5%. Initially, water-soaked, brown, stripe-like lesions developed on tender rachides, petioles, subsequently spreading rapidly to adjacent young leaves. Then, affected tissues gradually curled and desiccated. Eighteen diseased samples were collected from Zhanjiang (110.33°E, 21.28°N), surface sterilized using 70% ethanol for 30 s followed by 2% sodium hypochlorite (NaOCl) for 5 min, rinsed three times with sterile distilled water, plated onto PDA, and incubated at 26 °C for 3 days. Fungal colonies were subcultured onto PDA and grown for 5 days. Twenty-six isolates with similar morphological characteristics were obtained. On PDA, colonies exhibited earth-yellow, cottony aerial mycelium. Then, the fungi were cultured on Spezieller Nährstoffarmer agar (SNA) (Leslie and Summerell. 2006) and carnation leaf agar (CLA) (Fisher et al. 1982) at 26 °C for 10 days. Conidiogenous cells (n= 50) were phialidic, with a length of 3.08 to 46.72 µm on SNA and 3.34 to 41.56 µm on CLA. Macroconidia (n= 50) were falcate, slightly curved, tapering apically with 1 to 5 septa, 16.05 to 37.25 µm×2.59 to 4.86 µm on SNA and 17.12 to 37.13 µm×2.77 to 4.45 µm on CLA. Chlamydospores were spherical and arranged in chains on both media. These characteristics were consistent with those described for Fusarium pernambucanum (Santos et al. 2019). The TEF-1α (PV995092, PV995095, PV995098), RPB2 (PV995091, PV995094, PV995097), and calmodulin (PV995090, PV995093, PV995096) were amplified using the primers TEF1/TEF2 (O’Donnell et al. 1998), 5F2/7cR and CL1/CL2 (Pedrozo et al. 2015), respectively. BLAST analysis against the GenBank database revealed that the TEF-1α, RPB2, and calmodulin gene sequences shared 99.29% to 100% sequence identity with F. pernambucanum reference strains CBS 791.70, CBS 132194, CBS 132894, and CBS 133024. Phylogenetic analysis, based on a concatenated alignment of the three genes from 26 Fusarium species, placed isolates HSD-5, HSD-16, and HSD-23 within a well-supported clade together with F. pernambucanum. For pathogenicity assays, spore suspension (1×10⁶ conidia/mL) was sprayed onto 1-month-old peanut plants, with 10 plants inoculated per isolate and 10 control plants treated with sterile distilled water. All plants were maintained in a greenhouse at 26 °C under 90% relative humidity. Five days post-inoculation, inoculated plants exhibited water-soaked lesions on tender rachises and petioles. Under continuous moisture, disease symptoms progressed rapidly, with visible development of white mycelium at infected sites. When moisture supply was discontinued, affected tissues curled and gradually desiccated, displaying symptoms consistent with those observed in natural field infections. No symptoms were observed in control plants. The fungus was reisolated from disease tissues and confirmed as F. pernambucanum based on sequence analysis of the TEF-1α gene. No F. pernambucanum isolates were obtained from control plants. F. pernambucanum has previously been reported as a causal agent of flower dry rot in Passiflora edulis (Liu et al. 2021) and peduncle rot in grape (Wang et al. 2024). To our knowledge, this is the first report of F. pernambucanum causing top rot on peanut in China. The investigation confirmed the presence of the disease in multiple peanut-producing counties within Zhanjiang City, with yield losses ranging from 2.5% to 4.5%. No cases were detected in any other part of Guangdong Province. The identification of this pathogen may provide critical information for developing effective disease management strategies.