Zebra plant (Calathea zebrina Sims Lindl.) is widely grown in China as a valuable houseplant. In August 2025, anthracnose was observed in a landscape garden in Shenzhen (22°35'55"N, 113°59'21"E), Guangdong Province. An ~900 m2 survey found ~50% of plants infected, with 20 to 50% of the leaf area showing necrotic lesions. Initial symptoms appeared as small yellow spots on the leaves, which gradually enlarged and elongated into irregular lesions, 0.4 to 5 × 0.2 to 2 cm. The spots became dark brown with a yellow halo, and the affected leaves withered and died. Ten diseased plants were collected, and each leaf segment (5 × 5 mm2) from the lesion margins was disinfected with 1% NaClO for 1 min and 70% ethanol for 30 s, washed with sterile distilled water, placed on PDA and incubated at 25 °C. After 3 days, three fungal strains (MBSZU 25-052 to 25-054) exhibiting similar morphology were obtained, with an isolation frequency of 75% from 20 tissue samples. Colonies on PDA reached 85 to 90 mm after one week at 25 °C, white with cottony mycelia, raised with an entire margin, and with a white reverse. Appressoria were oval to irregular, dark brown to black, and 6 to 14 × 4.5 to 8 µm. Conidiophores were septate, branched, and hyaline to brown. Conidiogenous cells were cylindrical to ampulliform, hyaline, and 6 to 30 × 1.8 to 4 µm. Conidia were hyaline, one-celled, cylindrical, ends rounded, aseptate, smooth-walled, guttulate, and 10 to 15 × 4.1 to 5.8 µm (n = 50). Morphologically, all strains resembled Colletotrichum spp. (Weir et al. 2012). ITS, ACT, CAL, CHS-1, TUB2, GAPDH, and ApMat genes were amplified using the primer pairs ITS5/ITS4, ACT-512F/ACT-783R, CL1C/CL2C, CHS-79F/CHS-345R, T1/T22, GDF1/GDR1, and AMF1/AMR1, respectively (Silva et al. 2012; Weir et al. 2012) and deposited in GenBank (ITS: PX363174 to PX363176; ACT: PX393134 to PX393136; CAL: PX393137 to PX393139; CHS-1: PX393140 to PX393142; TUB2: PX393143 to PX393145; GAPDH: PX393146 to PX393148; ApMat: PX401953 to PX401955). BLAST analysis revealed that the ITS, ACT, CAL, CHS-1, TUB2, GAPDH, and ApMat sequences matched C. tropicale (CBS 124949) with similarities of 99.65, 99.64, 98.73, 98.66, 99.71, 97.87, and 99.88%, respectively. Phylogenetic analyses confirmed that all strains as C. tropicale. To test pathogenicity, both wounded and unwounded healthy leaves were used in this experiment. All leaves were wiped with 0.1% NaClO and rinsed three times with sterile water. A conidial suspension (15 µl of 106 conidia/ml) from 2-week-old cultures was applied to each leaf using the attached leaf assay. Control leaves were mock-inoculated with sterile distilled water. Each treatment was performed with ten replicate plants and repeated twice. Plants were incubated at 25 °C under a relative humidity of 80 to 85%. After seven days, all inoculated leaves developed brown lesions with yellow halos, consistent with those observed in the field, whereas the control leaves remained asymptomatic. C. tropicale was reisolated and confirmed by morphology and DNA sequencing, thereby fulfilling Koch’s postulates. To our knowledge, this is the first report of leaf anthracnose on C. zebrina caused by C. tropicale in China and worldwide. C. tropicale has a wide host range in tropical regions (Jayawardena et al. 2021). This finding highlights a potential threat to the cultivation of this widely grown ornamental plant in China and other tropical regions, emphasizing the need for monitoring and management strategies to prevent economic and aesthetic losses.
Khuna et al. (Sat,) studied this question.