First Report of Anthracnose Caused by Colletotrichum siamense and C. fructicola of Camellia chrysantha in China

Camellia chrysantha (Hu) Tuyama, belonging to the Theaceae family, is famous for its large size and golden yellow flowers, which has high ornamental and health care functions (Mo et al. 2013). Anthracnose is one of the most important fungal diseases worldwide, causing serious economic losses to many plants. In October 2019, severe anthracnose symptoms were observed on the leaves of C. chrysantha in a 0.6 hectare field with 15-20% disease incidence in Fangchenggang city, Guangxi Zhuang Autonomous Region of China. Diseased leaves initially appeared irregular chlorotic spots, which afterwards enlarged and coalesced. Finally, the spots became dark brown or black, sunken lesions (8-22 mm in diameter), and covered with plenty of acervuli. For pathogen isolation, the leaf lesions were cut into small tissue pieces (5 mm×5 mm), disinfected by 0.3% sodium hypochlorite for 2 min and 70% ethanol for 40 s, rinsed in sterile distilled water, and then incubated at 28°C on potato dextrose agar (PDA) plates. A total of 7 fungal isolates with whitish to light grey, dense colonies were recovered at 5 days. These isolates were tentatively identified as belonging to Colletotrichum gloeosporioides species complex through morphological and cultural characters (Weir et al. 2012). The conidia were nonseptate, cylindrical with obtuse to rounded ends, 13.9 to 18.3 (average 16.1) μm × 4.5 to 6.2 (average 5.4) μm (n = 50). For further precise identification, the 7 Colletotrichum isolates were analyzed using partial sequences of genomic loci including the internal transcribed spacer (ITS), β-tubulin (TUB), calmodulin (CAL), actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glutamine synthetase (GS), and the mating type locus MAT1-2 (ApMat) genes (Liu et al. 2015). The amplification sequences were compared with the sequences registered in the GenBank database based on nucleotide similarity. The above sequences of 4 isolates (JZB-PF4232, JZB-PF2231, JZB-PF42 and JZB-PF22) had 99-100% identity to the sequences of Colletotrichum siamense strains retrieved from GenBank, while the sequences of the other 3 isolates (JZB-PF3231, JZB-PF32 and JZB-PF41) showed over 99% identity with those of the C. fructicola strains. All the sequences were deposited in GenBank with accession number MT708987 to MT709007, MW149430 to MW149433, and MW142259 to MW142282. A multi-loci phylogenetic analysis of the concatenated sequences of ITS, TUB, CAL, ACT, GAPDH, GS and ApMat genes placed the 4 isolat