First Report of Leaf Spot on Radix Asteris (Aster tataricus) Caused by Colletotrichum destructivum in China

Aster tataricus is a perennial herb belonging to the family Asteraceae. It is an important plant for traditional Chinese medicine. A decoction of the roots is used in treating chronic bronchitis, cough, and phlegm. It also has antitumor, antibacterial, antiviral, and antioxidant properties (Zhang et al. 2012). In 2014 and 2015, dark brown lesions were observed on leaves of A. tataricus plants in Changchun (125.39°E, 43.45°N), Jilin Province, China. The disease incidence reached approximately 30%. Symptoms on diseased leaves initially included small, light brown, and circular spots. As the disease progressed, small circular spots expanded and gradually became round or irregular, and the spots turned gray in the center with dark brown margins, frequently surrounded by light yellow haloes. Eventually, the necrotic areas often coalesced and resulted in the appearance of larger spots with a diameter of 4.0 to 15.0 mm. Severely affected leaves often withered and died. Leaf tissues (3 × 5 mm²), cut from the margins of lesions, were surface disinfected (75% ethanol for 30 s, 1% NaClO for 1 min, rinsed three times with sterile distilled water) and placed on potato dextrose agar (PDA). Single conidial isolate CDAT137107 was grown on PDA under a 12-h photoperiod at 25°C. The mycelia were initially pale white, and the colony gradually expanded and turned into black, with some small black structures. On synthetic nutrient-poor agar (Liu et al. 2016), the conidiophores of the fungi were cannular, hyaline, and septate. Conidia (n = 150) were straight, cylindrical, both sides obtuse, with two oil droplets, and measured 8.9 to 37.5 (14.6 ± 3.8) μm in length, and 3.0 to 17.3 (4.9 ± 1.6) μm in width. Appressoria were brown sticks and measured at 4.9 to 7.5 × 4.7 to 7.0 μm. Setae were slender, straight, subulate, dark brown, measured at 59.5 to 120.5 × 3.2 to 6.5 μm. Based on the morphological characteristics, the fungus was preliminarily identified as Colletotrichum destructivum (Damm et al. 2014). The internal transcribed spacer (ITS, KT355798) and chitin synthase (CHS-1, KT355799) sequences matched to C. destructivum (EU400156, JQ005785) with 100% identity, and the beta-tubulin (tub2, KT633397) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH, KT751006) sequences matched to C. destructivum (JX625198, KC843523) with 99% identity. Pathogenicity tests were performed by spraying a 10⁶ conidia/ml suspension of CDAT137107 on 30 healthy leaves of A. tataricus var. petersianus, and the controls were sprayed with sterilized water. All the inoculated leaves were covered with plastic bags and incubated in a growth chamber at 25°C for 7 days at 95% relative humidity. Symptoms on the inoculated leaves were similar to those that naturally occurred in the field, and there were no symptoms on the control leaves. The fungus was reisolated from the infected leaves, which was similar to the inoculated isolate. C. destructivum has been reported on curly dock in Korea and on common thyme in Florida (Fu et al. 2015; Lee et al. 2002). To our knowledge, this is the first report of C. destructivum causing anthracnose of A. tataricus. There is a need to develop disease management strategies for anthracnose on A. tataricus to prevent major economic constraints on production and quality of this medicinal plant in China.