First Report of Anthracnose on Boehmeria nivea Caused by Colletotrichum higginsianum in China

Abstract

Ramie (Boehmeria nivea (L.) Gaud) anthracnose is regarded as one of the most widely spread and devastating diseases of ramie. This disease is most severe during warm and humid conditions. In China, ramie anthracnose is found in approximately 10,000 ha, with yield losses averaging 20% and ranging as high as 55% in some fields (3). In September 2010, typical anthracnose symptoms were observed in cultivated fields near Xianning, HuBei Province, China. Lesions on diseased leaves were initially small, scattered, bluish white, and water soaked. As the disease progressed, irregular spots developed on the leaves and the spots turned gray in the center with a brown margin. The diameter of the lesions was approximately 1 to 3 mm. Initially, lesions on the stems were fusiform and then expanded, causing the stem to break. Leaf and stem tissue adjacent to and including lesions were surface disinfected in 0.1% sodium hypochlorite and then planted on potato dextrose agar (PDA) plus oxalic acid to inhibit bacterial growth. The plates were incubated at 25°C for 3 to 5 days until the appearance of pink spore masses with numerous dense clusters of black setae. On PDA, the fungus initially produced gray colonies with an orange conidial mass and then the colonies turned black after 5 days. Spores were single celled, colorless, straight, oval, obtuse at both ends, 10.0 to 20.0 × 3.0 to 5.0 μm with an average size of 15.8 ± 2.4 × 4.6 ± 0.4 μm, and a length/width ratio of 3.47 ± 0.62. The setae were dark brown, 1 to 3 septa. These morphological traits corresponded to Colletotrichum higginsianum Sacc (1). The ITS1, 5.8S, and ITS2 sequences with primers ITS1 and ITS4 of this fungus (GenBank Accession No. JF830783) were 99% similar to sequences of multiple isolates of C. higginsianum (GenBank Accession Nos. GU935872 and AB042303). In pathogenicity tests, both sides of ramie plant leaves from 10-day-old, 30-cm high plants were sprayed with conidial suspensions (1 × 106 conidia/ml) of a representative fungal isolate. This experiment was repeated three times. Inoculated plants were incubated in an artificial climate chamber with a 12-h photoperiod at 25 to 28°C and a relative humidity of 90%. Three days after inoculation, brown spots and water-soaked lesions were observed on all inoculated leaves, but no symptoms were seen on water-treated control plants. Koch's postulates were fulfilled by the reisolation of C. higginsianum from diseased leaves. C. higginsianum is known to cause anthracnose leaf spot disease on many cultivars of Brassica and Raphanus spp., but there have been no reports on it causing ramie anthracnose. C. boehmeriae Sawada and C. gloeosporioides Penz are known to be the agents of ramie anthracnose (2,3). To our knowledge, this is the first report of C. higginsianum causing anthracnose of ramie in China and in the world. References: (1) A. J. Caesar et al. Plant Dis. 94:1166, 2010 (2) R. M. Li and H. G. Ma. J. Plant Prot. 20:83, 1993. (3) X. X. Wang et al. Plant Dis. 94:1508, 2010.