First Report of Fusarium pernambucanum Causing Root Rot on Cowpea in China

Vigna unguiculata (L.) Walp. (cowpea) is widely cultivated in Sanya City, Hainan Province, primarily as a vegetable crop. In December 2024, root rot (locally called red root disease, 5%–20% incidence) was surveyed in Yazhou District, Sanya City (18.35°N, 109.22°E). Early infected plants shed fibrous roots with slight brown basal rot and mild chlorosis, whereas advanced infections caused reddish-brown constricted basal decay, leaf marginal yellowing and severe whole-plant wilt. Lesion-border basal stem tissues from three cowpea cultivars (CJL-13, CJL-40 and CJL-41) were surface disinfected (75% ethanol for 30 s, hypochlorous acid solution with 0.02% available chlorine for 1 min, rinsed three times with sterile water) and incubated on potato dextrose agar (PDA) at 28 ℃. After 5‑day incubation, a single representative isolate FVu1 with unique morphological features was purified via hyphal tipping for subsequent morphological, molecular and pathogenic characterization. Its colony was initially white, then gradually turned yellow, and finally became brownish-yellow. On potato dextrose water, macroconidia were falcate, 3–5 septate, 25–40 × 5–7 µm, consistent with Fusarium spp. (Leslie and Summerell 2006). Genomic DNA was extracted from a purified single colony. Four gene loci, including ITS, TEF1-α, TUB2 and RPB2, were amplified using primer pairs ITS1/ITS4 (Schoch et al. 2012), EF-728F/EF2 (O’Donnell et al. 1998), Bt-2a/Bt-2b (Glass and Donaldson 1995), and F.RPB2-F/F.RPB2-R (O’Donnell et al. 2010). PCR products were sequenced and deposited in GenBank. Sequence files were compared against the NCBI ITS database using the NCBI BLAST program. A phylogenetic tree was constructed with MEGA11.0 software using the neighbor-joining method (bootstrap replicates ≥ 1000) (Saitou and Nei 1987). The ITS (PX488449), TEF1-α (PZ014380), TUB2 (PZ014381), and RPB2 (PZ014382) sequences of isolate FVu1 shared 99.80%, 99.17%, 98.83% and 99.38% nucleotide identity with reference sequences of Fusarium pernambucanum, respectively. In the phylogenetic tree (Figure 2), isolate FVu1 clustered with known strains of Fusarium pernambucanum with high bootstrap support, providing strong molecular evidence for the species affiliation of strain FVu1. Pathogenicity tests were conducted by root-wounding inoculation. A sterile blade was inserted into the substrate approximately 1 cm from the stem base to slightly damage the root system, and 2 mL of spore suspension (1 × 10⁶ conidia mL⁻¹) was pipetted around the wounded roots. Seedlings treated with sterile water served as controls. A total of 89 cowpea accessions, including the three naturally infected cultivars, were evaluated. Inoculated plants developed basal rot, root necrosis, and wilting, whereas water-treated controls remained asymptomatic. Symptoms mirrored those observed in the field. Following Koch’s postulates, the pathogen was re-isolated from infected root tissues of inoculated plants. Morphological comparison showed that the re-isolated strains shared highly consistent morphological features with the original isolate FVu1. To our knowledge, this study represents the first report of cowpea root rot caused by Fusarium pernambucanum in mainland China and provides a reference basis for the monitoring and management of this disease.