First Report of Anthracnose Caused by Colletotrichum karstii on Taxus wallichiana var. mairei in Sichuan, China

Taxus wallichiana Zucc. var. mairei (Lemée & H. Léveillé) L. K. Fu & Nan Li, an endangered conifer, is exploited in different ways, such as wood, medicinal, and ornamental uses (Yang et al. 2016; Zhang et al. 2017) and is naturally distributed along the Yangtze River Valley. In October 2018, anthracnose-like symptoms were observed on about 3% of T. wallichiana var. mairei leaves from a single tree in a courtyard, where there were 10 diseased trees in total, in Zizhong County (Sichuan Province), China. The leaves were originally chlorotic and changed from pale green to dirty red, and they eventually died and fell off. Subsequently, the adjacent twigs wilted and died. Three single conidial isolates were established from infected leaves for morphological observations. Colonies incubated on potato dextrose agar (PDA) at 25 ± 1°C were white to gray and yellow on the bottom. Conidia measured 11.49 to 16.39 × 5.61 to 6.96 μm (n = 20), hyaline, unicellular, cylindrical, and sclerotia and setae were absent. Appressoria were brown, circular to clavate, 7.25 to 12.54 × 5.93 to 9.8 μm (n = 20). Its teleomorph occurred until 3 weeks of incubation. The ascomata were brown to dark brown, usually global, superficial or immersed in PDA. Asci measured 56.22 to 77.35 × 10.56 to 15.40 μm (n = 20), unitunicate, thin-walled, eight-spored, and clavate. Ascospores 10.8 to 20.29 × 4.53 to 8.53 μm (n = 50), one-celled, hyaline, slightly curved. Hyphopodium was irregular, usually with a light serrate margin. Genomic DNA of the representative isolate SICAUCC 18-0009 was extracted, and the internal transcribed spacers (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), chitin synthase (CHS-1), beta-tubulin (TUB2), calmodulin (CAL), and actin (ACT) genes were amplified with the primers as described in White et al. (1990), Guerber et al. (2003), Weir et al. (2012), O’Donnell and Cigelnik (1997), and Carbone and Kohn (1999), respectively. The generated sequences were deposited in GenBank with accession numbers MK346320 (ITS), MK359214 (GAPDH), MK359213 (CHS-1), MK359212 (CAL), MK359211 (ACT), and MK359210 (TUB2). BLAST analyses showed high homology with previously deposited sequences of Colletotrichum karstii: ITS, KX578788 (100%), KX578794 (100%); GAPDH, KX578772 (100%); CHS-1, JX863685 (100%); CAL, HM582009 (100%); ACT, HM581993 (99%); and TUB2, HM585428 (100%). The fungus was identified as C. karstii based on morphological and phylogenetic analyses (Yang et al. 2011). To verify pathogenicity, 20 healthy leaves were sprayed with conidial suspension (1 × 10⁴ conidia/ml) of the isolate SICAUCC 18-0009, and an equal number of leaves were sprayed with sterilized distilled water as the control. Plants were incubated in a growth chamber at 25 ± 1°C and 95% relative humidity with a 12-h photoperiod. The leaves showed light brown lesions at the third day, and 7 days later, symptoms identical to those in the wild developed, whereas the controls remained asymptomatic. The fungus reisolated from the infected leaves was identified as previously described. To our knowledge, this is the first report of anthracnose on T. wallichiana var. mairei caused by C. karstii. This disease is a potential threat to the management of T. wallichiana var. mairei.