First report of <i>Idesia polycarpa</i> fruit anthracnose caused by <i>Colletotrichum godetiae</i> in Guizhou Province, China

Idesia polycarpa Maxim. (Flacourtiaceae) is a deciduous tree whose fruits have a high oil content and good health effects (Wu et al. 2018). In September 2023, anthracnose lesions were observed on I. polycarpa fruits with approximately 60% incidence on about 300 trees in a 170-ha planting base in Guiding city (26°33′N, 107°13′E), Guizhou Province, China. The initial symptoms were necrotic spots on the fruits, which gradually expanded and enlarged into subcircular or irregular, sunken, black lesions. Symptomatic fruits (n=20) were collected from 10 trees, and surface disinfected with 70% ethanol for 30 s, followed by 1% NaClO for 60 s, rinsed 3 times with sterile water, and then air-dried and placed on potato dextrose agar (PDA) medium and incubated at 25°C, 12 h light/dark cycle for 3 d. Then emerging fungal colonies were sub-cultured into fresh PDA medium to obtain pure isolates. Fungal colonies on PDA of three similar obtained isolates (DSG7-1, DSG7-2 and DSG7-3) were gray-white and exhibited cottony mycelia, with orange pigmentation at the back and melanin deposition. Conidia were one-celled, hyaline, cylindrical, and acute at one or both ends, and mostly 14.59 to 21.23 µm in length and 4.77 to 7.55 µm in width (n = 50). Appressoria were oval to irregular in shape and dark brown, and mostly 7.23 to 13.40 µm in length and 5.64 to 8.98 µm in width (n = 30). Based on morphological, cultural and microscopic characteristics, the isolates were found to be consistent with those reported for the Colletotrichum acutatum species complex (Damm et al. 2012). For molecular identification, DNA of the three representative isolates were extracted. The rDNA internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), and histone 3 (HIS3) genes were amplified with the primers ITS1/ITS4 (White et al. 1990), GDF/GDR (Templeton et al. 1992), ACT-512F/ACT-783R (Carbone and Kohn 1999), and CYLH3F/CYLH3R (Crous et al. 2006) primers. The sequences of ITS, GAPDH, ACT and HIS3 were deposited in GenBank (DSG7-1: PV691519, PV690013, PV690016 and PV683045; DSG7-2: PV682697, PV690014, PV690017 and PV690011; DSG7-3: PV682700, PV690015, PV690018 and PV690012). BLASTn results showed the sequences of DSG7-1 were highly identical to those sequences of C. godetiae CBS 129911 (MH865663.1 [ITS], 552/552; JQ949755.1 [ACT], 247/247; JQ948765.1 [GADPH], 251/252; JQ949425.1 [HIS3], 379/382). The phylogenetic tree constructed with the software MEGA X using the maximum-likelihood method indicated the three isolates gathered into one branch with C. godetiae. Based on these results, the three isolates were identified as C. godetiae. To confirm pathogenicity, spore suspensions (1×106 spores/mL) of DSG7-1 were sprayed on healthy fruits (n=50), while an equal volume of sterile water was sprayed on the control (n=10). All inoculated fruits showed similar anthracnose symptoms within 6 d, whereas controls showed no symptoms. The reisolated fungal culture was identical in morphology and ITS sequence to DSG7-1, thus fulfilling Koch’s postulates. C. godetiae has been already reported as a plant pathogen causing walnut anthracnose in Guizhou Province (Zhang et al. 2024). But to our knowledge, this is the first report of C. godetiae causing I. polycarpa fruit anthracnose in China, providing a theoretical basis for the disease management, which might limit fruit growth, ultimately leading to an oil production decline in I. polycarpa.