First report of Septoria pachyspora causing leaf blotch of Zanthoxylum schinifolium

Zanthoxylum schinifolium is cultivated for its seed oil in Korea. The oil is used for medicinal purposes and in special cuisines and consequently is highly valued in the market. Rust caused by Coleosporium zanthoxyli is the only disease recorded on this tree in Korea so far (Cho & Shin, 2004).

In 2001, several Z. schinifolium leaves with leaf blotch symptoms were found in Goseong, Korea. The pathogen was identified as a Septoria sp. by preliminary microscopy; however, pathogenicity was not confirmed. In August 2005, a number of 10 to 15 year-old trees in Hongcheon, Korea, were found to have typical leaf blotch symptoms, causing premature defoliation. Initial symptoms were circular, brown to dark brown leaf spots, later expanding to occupy half of the leaf. Numerous black conidiomata with conidial horns were formed on the surface of the lesion (Fig. 1).

Single conidial isolates formed dark greyish colonies on potato dextrose agar (Fig. 2). Conidiomata matured after 5 weeks when plates were incubated under fluorescent illumination for 12 hr photoperiods at 25°C. Conidiomata were pycnidial, amphigenous, 85-140 µm in diameter. Conidia were curved to substraight, guttulate, subhyaline, 30-64×2-3 µm, 2-7 septate (Fig. 3). Based on the morphological and cultural characteristics, the isolates were identified as Septoria pachyspora (Saccardo, 1895; Greene, 1964). The collection from 2001 coincided with the 2005 collection in terms of leaf symptoms as well as morphology of conidiomata and conidia. Voucher specimens are housed at Korea University (SMK 18664, 21293) and a conidial isolate is kept in the Korean Agricultural Culture Collection of the National Institute of Agricultural Biotechnology (KACC 42510).

Pathogenicity was confirmed by wound-inoculating the leaves of three 2-year-old seedlings with a conidial suspension (ca. 2×10⁵ conidia/ml). Three non-inoculated seedlings served as controls. The plants were maintained in a glasshouse at 100% relative humidity for 48 hrs. After 8 days, typical leaf blotch symptoms, identical to the ones observed in the field, started to develop on the leaves of inoculated plants (Fig. 4). No symptoms were observed on control plants. Septoria pachyspora was reisolated from the lesions of inoculated plants.

A leaf spot disease associated with S. pachyspora has previously been recorded on Z. americanum in North America (Greene, 1964) and on Z. ailanthoides in Japan (Kobayashi et al., 1983). This is the first report of S. pachyspora causing leaf blotch on Z. schinifolium in Korea and in the world.