First report of leaf anthracnose caused by Colletotrichum boninense on spindle trees

In autumn, 2003 and continuing on to next spring, leaf anthracnose was observed on spindle tree (Euonymus japonica) leaves on Kwanak Mountain, Seoul, Korea. The leaf spots were more severe on leaves near the ground and progressed to the upper leaves (Fig. 1). The causal fungus was aseptically isolated from the leaf spot lesions and cultured on potato dextrose agar (PDA). As shown in Fig. 2, the colony on PDA was whitish at the margin, cream-to-dull orange or black/brown, with dark areas of acervuli. Conidia were formed in black/orange masses and measured 13-17 x 5-7 μm in size. Dark brown setae were frequently observed on PDA and ranged up to 100 μm in length. When the 18S rDNA ITS sequence of the causal fungus was compared with eleven isolates of C. boninense retrieved from GenBank, the intraspecific DNA homologies were 97.4 to 99.6%. When compared with related species such as C. gloeosporioides, C. musae, C. fragariae, C. spinaceae and C. lindemuthianum, the interspecific DNA homologies were 93.9, 91.7, 93.6, 92.6 and 88.7%, respectively. Based on morphological, cultural and molecular characteristics, the fungus was identified as C. boninense, as described by Moriwaki et al. (2003).

For the pathogenicity test, 3-to-4 year old spindle tree leaves were inoculated with a conidial suspension (10⁸ per ml) and kept for one week in a moist chamber at 25°C. Similar symptoms were observed on treated leaves and the causal fungus was re-isolated from leaf lesions. No symptoms were observed on uninoculated control plants.