First Report of Colletotrichum truncatum Causing Stem Anthracnose of Cowpea ( Vigna unguiculata ) in Florida, U.S.A.

Cowpea ( Vigna unguiculata (L.)) is an important high-protein food and cover crop in Florida’s vegetable and row-crop systems, well adapted to the state’s sandy soils and subtropical climate (Wang et al. 2004; Weng et al. 2019). In August 2025, symptomatic plants (~20) from a commercial field in Levy County were submitted to the UF/IFAS Plant Pathology Extension Laboratory for diagnosis, where disease incidence was estimated at 20–30%. Affected plants showed severe wilting and dark brown sunken stem lesions while leaves remained symptomless. Abundant acervuli with dark brown setae were observed in lesions. The pathogen was isolated from advancing lesion margins, surface sterilized in 1% sodium hypochlorite on quarter-strength PDA, and single-conidium cultures were obtained. Colonies were white, becoming dark gray with concentric zonation after 10 days of incubation. Acervuli were abundant and scattered, with dark brown conidiomata with pointed setae. Conidiophores pale brown, septate, and branched. Conidia (17.1–21.2 × 2.5–3.3 μm) hyaline, smooth-walled, aseptate, and distinctly falcate in shape. Phenotypical features of isolates were similar to C. truncatum (Damm et al. 2009). Molecular characterization included PCR amplification and sequencing of the ITS region and two additional loci, glyceraldehyde-3-phosphate dehydrogenase ( GAPDH ) and actin ( ACT ) (White et al. 1990; Vieira et al. 2020). BLASTn analysis of the obtained sequences (ITS: PZ277487, PZ277488, 537 bp; GAPDH : PZ242905, PZ242906, 292 bp; and ACT : PZ320977, PZ320978, 284 bp) showed high identity to the ex-type strain C. truncatum CBS 151.35, including 99.62% for the ITS region (GU227862, 520/522 bp), 99.61% for GAPDH (GU228254, 253/254 bp), and 98.80% for ACT (GU227960, 246/249 bp). Phylogenetic analysis confirmed that the isolates clustered with C. truncatum 151.35 with 100% bootstrap support. Pathogenicity tests were performed on six-week-old cowpea (US-1138) seedlings using conidial spray inoculation (1×10⁵ conidia/ml) and agar-block inoculation (5 mm mycelial plugs) with nine plants per inoculation method, including the control. Control plants were sprayed with sterile distilled water or treated with sterile agar alone. All plants were covered with a plastic bag for 12 hours in a climate-controlled greenhouse (12-h/12-h daylight, 27°C, and >70% RH), and the experiment was repeated twice with the same design. Spray-inoculated plants developed discoloration at leaf nodes by four days post-inoculation, progressing to brown sunken stem lesions with abundant acervuli. Agar-block inoculations produced lesions within two days. Severe infections caused rapid wilting and plant death within six days. No symptoms were observed in mock-inoculated control plants. Symptoms in inoculated plants were consistent with those observed in field-infected samples, with all lesions restricted to the stem tissue. The pathogen was reisolated from symptomatic tissues and its identity confirmed. C. truncatum is known to infect several Fabaceae species in Florida but has not previously been reported on cowpea in the state and has been documented only in a limited number of countries (Alfieri et al. 1994; Farr and Rossman 2018). To our knowledge, this is the first report of C. truncatum affecting cowpea in Florida, USA. Given the economic and cultural importance of cowpea in the southern United States, this report highlights the crop’s high susceptibility and the implications for growers.