First Report of Anthracnose Caused by Colletotrichum truncatum on Echeveria amphoralis in Mexico

Echeveria amphoralis, which is native to Mexico, holds economic importance as a potted plant and cut flower due to its drought tolerance and aesthetic appeal (Reyes et al. 2011). In July 2025, a random sampling was conducted on 1,000 plants within a 0.5-ha area at the Center of Research in Horticulture and Native Plants of UPAEP (18°55'56.1"N, 98°24'02.3"W). The 180-day-old E. amphoralis plants exhibited leaf anthracnose, with a disease incidence and severity (visually estimated) of 45% and 50%, respectively. Symptoms consisted of sunken, necrotic, reddish-brown lesions containing concentric rings with acervuli and masses of conidia, which coalesced and led to defoliation. From 50 symptomatic plants, 5-mm-diameter sections of symptomatic tissue were excised, disinfested with 3% NaOCl, rinsed with sterile distilled water, dried, placed on potato dextrose agar plates, and incubated at 26º C for 10 days in darkness. Fifty isolates, one from each symptomatic plant, were obtained using hyphal tip culture. After 10 days, all colonies were round with smooth margins, grayish-white, turning dark gray with age, producing orange conidial masses. Conidia (n=100) were smooth, curved, hyaline, aseptate, with a conical tip and truncated base, measuring 22.4-25.7 × 2.9-3.6 μm., originating from dark brown acervuli, with straight, septate setae. Based on these morphological characteristics, the isolates were tentatively identified as Colletotrichum truncatum (Damm et al. 2009). A representative isolate (CtEa14) was selected for molecular identification, and genomic DNA was extracted using the CTAB protocol. The internal transcribed spacer (ITS) region and the β-tubulin (TUB2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and actin (ACT) genes were amplified, sequenced (Natesan et al. 2025), and deposited in GenBank, ITS: PZ043885 (542 bp); TUB2: PX597404 (476 bp); GAPDH: PX597403 (273 bp); ACT: PX548792 (276 bp). BLAST analysis from partial sequences showed a 100% shared identity with isolates of Colletotrichum truncatum; MN148631 (Yu et al. 2020), KX786456 (Santos et al. 2018), OP495668 (Shahriar et al. 2023), OR147336 (Martins et al .2024). Pathogenicity was confirmed by inoculating the surface of four leaves on each healthy 180-day-old E. amphoralis plant (n=20), grown in pots with sterile soil, with 20 µl of a suspension (1×10 6 conidia/ml) of isolate CtEa14. Four leaves of each of five control plants were inoculated with sterile distilled water and served as negative controls. After 11 days of incubation in a greenhouse at 26°C and 90% relative humidity, all inoculated plants displayed sunken, necrotic, reddish-brown lesions and concentric rings of conidia, consistent with the initial symptoms observed in the field. No symptoms developed on the negative controls. The fungus was reisolated from the inoculated plants and confirmed as C. truncatum through the morphological and molecular characterization described above, thereby fulfilling Koch's postulates. Pathogenicity tests were performed three times. Although C. truncatum has been reported to cause anthracnose in Cyamopsis tetragonoloba in Mexico (García et al. 2022), to our knowledge, this is the first report of anthracnose in E. amphoralis in Mexico. This research is crucial for developing integrated management strategies for this disease and preventing its spread to other production areas.