First Report of Anthracnose on Wurfbainia villosa var. villosa Caused by Colletotrichum gloeosporioides in China.

Wurfbainia villosa var. villosa is a traditional Chinese herbal medicine under the family Zingiberaceae, and its ripe fruits (called Fructus Amomi) are widely used clinically for the treatment of gastrointestinal disorders (Yang et al. 2023; Chen et al. 2023). In September 2023, plants of W. villosa var. villosa exhibited anthracnose-like symptoms on leaf with a disease incidence of 35% (n = 100 investigated plants) in an approximately 90 m2 field in Guangning, China (N23°42'51.70″, E112°26'35.75″). Light yellowish-green spots (~2 mm diameter) initially appeared on the infected leaves, gradually formed sub-circular or irregular spots, then fused and expanded, resulting in wilting of the leaves. To identify the causal agent, 10 symptomatic leaves were collected and transferred to the laboratory. The symptomatic leaf samples were surface sterilized in 0.5% NaClO for 2 min, and in 70% ethanol for 30 s, then washed three times with sterile water and air-dried on sterile filter paper. The leaf tissues were placed on potato dextrose agar (PDA) medium containing 100 μg mL-1 of ampicillin (Sigma-Aldrich, St. Louis, MO) and incubated for 7 days at 28°C in darkness. Nine isolates with similar colony morphology were isolated from the 10 plated leaves. Three representative isolates (GNAF03, GNAF06, GNAF09 with approximately 3.5 cm in diameter after 3 days of incubation) appeared gray to dark brown with dense aerial hyphae at the front and gray to black colonies on the reverse of the plates. Conidia were cylindrical and measured 21.2 to 29.3 μm long × 7.1 to 9.6 μm wide (n = 50). Appressoria were formed by the tips of germ tubes or hyphae and were brown, ellipsoid, thick-walled, and smooth-margined, measuring 10.2 to 12.3 μm long × 6.4 to 8.2 μm wide (n = 50). Morphologically, the fungal isolates resembled Colletotrichum sp. (Weir et al. 2012). For molecular analysis, genomic DNA was extracted from fresh mycelia of the three isolates, and the primers ACT-512F/ACT-783R, CL1/CL2A, GDF/GDR, and ITS1/ITS4 were used to amplify partial regions of rDNA-ITS, actin (ACT), calmodulin (CAL), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) regions, respectively (Weir et al. 2012). The resulting sequences with more than 99% nucleotide identity to C. gloeosporioides were submitted to GenBank (accession numbers PP552725, PP552726, and OR827444 for ACT; PP552727, PP552728, and OR827443 for CAL; PP552729, PP552730, and OR827445 for GAPDH; PP549996, PP549999, and OR841394 for ITS). A phylogenetic tree was generated by the maximum likelihood method using the concatenated sequences of ACT, CAL, GADPH, and ITS by Polysuite software (Damm et al. 2020). Based on morphological and molecular analysis, the three isolates were characterized as C. gloeosporioides. The pathogenicity of the GNAF09 isolate was assessed on W. villosa var. villosa seedling leaves inoculated by spraying with 40 μL of conidial suspension at 106 conidia mL-1 or wounded with a sterile toothpick then inoculated with mycelial agar plugs (5 mm diameter). Control leaves were inoculated with 40 μL of sterile distilled water or agar plugs without mycelia. The inoculated plants were placed in a humid chamber at 28°C with 80% humidity and a 12 h light-dark photoperiod. Symptoms similar to those seen on naturally infected leaves were observed on all inoculated leaves after 7 days inoculation. Re-isolation was performed from 80% of the inoculated leaves and isolates were confirmed as C. gloeosporioides morphologically, confirming Koch's postulates, and by sequencing the ACT, CAL, GADPH, and ITS regions. The control groups remained asymptomatic. In previous studies, C. gloeosporioides has also caused anthracnose on Chinese medicinal plants, including Baishao (Radix paeoniae alba) (Zhang et al. 2017) and Rubia cordifolia L. (Tang et al. 2020). To our knowledge, this is the first report of C. gloeosporioides causing anthracnose on W. villosa var. villosa in China. The results of our report serve as valuable references for further research on this disease.