First report on leaf blight of Lindera obtusiloba caused by Pestalotiopsis microspora in Korea

Japanese spicebush (Lindera obtusiloba) is an ornamental shrub, growing wild in mountain areas all over the Korean peninsula, at elevations of between 100-1600 m above the sea level. Its leaves, fruit and stems have long been used for medicinal purposes in Korea. During autumn 2000 through 2005, severe outbreaks of leaf blight occurred sporadically at hillside localities in Gwangju, Gyeonggi province, Korea. Leaf symptoms began as grey or dark brown lesions, surrounded by yellowish halos; later enlarging, coalescing and becoming more irregular, until the whole leaf blighted (Fig. 1).

A fungus was consistently isolated from the leaf symptoms. It forms zonate colonies of whitish mycelia on PDA, later developing into yellowish colonies with small blackish acervular conidiomata. The conidia (Fig. 2) are 5-celled, fusiform, constricted at septa and 25.4-30.2µm ´ 4-8.9µm in size. The three median cells consist of two dark brown upper cells and one olivaceous bottom cell. The apical cell carries from 2 to 4 appendages, 24.6-29.1µm long and the basal cell a 4.5-6.9µm long, straight appendage (Fig. 3). These cultural and morphological characteristics are similar to those of Pestalotiopsis microspora (Keith et al., 2006), P. longiseta (Hamaya & Horikawa, 1982) and P. guepini (Mordue, 1971). The identity of our fungus was confirmed to be P. microspora by DNA sequencing of the internal transcribed spacer (ITS) region (GenBank accession number DQ456865), which was 100% homologous to those of other P. microspora isolates (Accession Nos AY924287.1, AY924286.1, AY924285.1, AY924280.1, AY924277.1, AY924270.1, DQ001009.1).

To confirm pathogenicity, detached shoots of Japanese spicebush were wound-inoculated by pin-pricking with a 5´10⁵ conidia per ml solution, prepared from a 4-week old P. microspora culture incubated at 25°C. Symptoms similar to the original ones started to appear after 5 days. Dark brown necrotic lesions with yellow-brownish peripheral halos were observed on inoculated leaves, while untreated leaves remained healthy (Fig.4). P. microspora was reisolated from the blighted leaves.

P. microspora is already known to be a pathogen of guava in Hawaii (Keith et al., 2006) but this is the first report on the fungus causing leaf blight on Japanese spicebush. The disease occurred sporadically, but very severely, at the sampling sites. It is still too early to assess the potential economic importance of the disease, but given its ability to produce severe outbreaks suggests that leaf blight may become a threat to Japanese spicebush in Korea in the future.