First Report of Anthracnose Caused by Colletotrichum gloeosporioides on Mikania micrantha in Guangdong, China

Abstract

Colletotrichum gloeosporioides is one of the most important pathogens in the world, capable of infecting at least 1,000 kinds of plants (Phoulivong et al. 2010). Mikania micrantha Kunth (Asteraceae), commonly known as mile-a-minute weed, is an extremely fast-growing, perennial creeping weed. Its native distribution is in Central and South America. It has been present in south China since the 1980s and has caused adverse impact on agricultural production in the established area (Li et al. 2013). In 2014, the incidence of anthracnose disease on M. micrantha reached 65 to 90% in Huizhou city, Guangdong, China, and plant mortality up to 45% was observed (Chen et al. 2006). The disease symptoms appeared as brown spots on the leaves and stems of M. micrantha; as the disease progressed, lesions turned dark brown. The location of the disease gradually expanded and even spread throughout the plant (Chen et al. 2006). Thirty symptomatic leaves were sampled from three regions: north of the city (Boluo, 114°28′ E, 23°18′ N), city center (Huidong, 114°72′ E, 22°98′ N), and south of the city (Huiyang, 114°43′ E, 22°80′ N) in Huizhou. Ten pieces from each leaf were surface sterilized with 70% ethanol for 30 s, and then they were rinsed in sterile distilled water and placed on potato dextrose agar (PDA) medium at 27°C in a dark chamber. Colonies grown on medium were round and carpetlike. Aerial hyphae grew more dense, and colonies became gray and black to dark green color. Conidia group showed visible pink and occasionally visible black dots scattered on the surface of the medium. Microscopic spores observed were cylindrical and colorless, 6 to 18 μm in length, and 3 to 5 μm wide. The identification of one representative isolate (H1) was determined by sequencing of the rDNA internal transcribed spacer regions 1 and 2 and the 5.8S using primers (White et al. 1990), and the sequence of each isolate was deposited in GenBank (accession no. KM501061). A BLAST search showed 100% identity with a C. gloeosporioides strain (accession no. KM357285.1). Isolate H1 was also confirmed as C. gloeosporioides with specific primers Colg 1 (5′-AACCCTTTGTGAACATACC-3′) and Colg 2 (5′-CCCTCCGGATCCCAG-3′) (Chen et al. 2006). The pathogenicity test of isolate H1 was carried out in a greenhouse. Ten plants were grown for 20 days in plastic pots (diameter 20 cm) in sandy soil (pH = 5.48) before inoculation. Isolate H1 was grown on PDA medium for 72 h, and the spores were harvested with sterile distilled water. Aqueous spore suspensions of isolate H1 were adjusted with deionized water to 1 × 10⁸ spores/ml and sprayed on the leaves of the plants. All the plants were then placed in the greenhouse at 25 ± 1°C and assessed for disease symptoms. The inoculated isolate caused symptoms identical to those observed in the field, and it was reisolated from the infected leaves and identified as previously described, and none of the untreated plants showed any signs of infection. To our knowledge, this is the first report of anthracnose caused by C. gloeosporioides on M. micrantha in China.