First Report of Leaf Blight Caused by Septoria allii on Garlic Chives in Korea

Abstract

Garlic chives, Allium tuberosum Roth., are widely cultivated in Asia and are the fourth most important Allium crop in Korea. In June 2011, a leaf blight of garlic chives associated with a Septoria spp. was observed on an organic farm in Hongcheon County, Korea. Similar symptoms were also found in fields within Samcheok City and Yangku County of Korea during the 2011 and 2012 seasons. Disease incidence (percentage of plants affected) was 5 to 10% in organic farms surveyed. Diseased voucher specimens (n = 5) were deposited at the Korea University Herbarium (KUS). The disease first appeared as yellowish specks on leaves, expanding to cause a leaf tip dieback. Half of the leaves may be diseased within a week, especially during wet weather. Pycnidia were directly observed in leaf lesions. Pycnidia were amphigenous, but mostly epigenous, scattered, dark brown to rusty brown, globose, embedded in host tissue or partly erumpent, separate, unilocular, 50 to 150 μm in diameter, with ostioles of 20 to 40 μm in diameter. Conidia were acicular, straight to sub-straight, truncate at the base, obtuse at the apex, hyaline, aguttulate, 22 to 44 × 1.8 to 3 μm, mostly 3-septate, occasionally 1- or 2-septate. These morphological characteristics matched those of Septoria allii Moesz, which is differentiated from S. alliacea on conidial dimensions (50 to 60 μm long) (1,2). A monoconidial isolate was cultured on potato dextrose agar (PDA). Two isolates have been deposited in the Korean Agricultural Culture Collection (Accession Nos. KACC46119 and 46688). Genomic DNA was extracted using the DNeasy Plant Mini DNA Extraction Kit (Qiagen Inc., Valencia, CA). The internal transcribed spacer (ITS) region of rDNA was amplified using the ITS1/ITS4 primers and sequenced. The resulting sequence of 482-bp was deposited in GenBank (JX531648 and JX531649). ITS sequence information was at least 99% similar to those of many Septoria species, however no information was available for S. allii. Pathogenicity was tested by spraying leaves of three potted young plants with a conidial suspension (2 × 105 conidia/ml), which was harvested from a 4-week-old culture on PDA. Control leaves were sprayed with sterile water. The plants were placed in humid chambers (relative humidity 100%) for the first 48 h. After 7 days, typical leaf blight symptoms started to develop on the leaves of inoculated plants. S. allii was reisolated from the lesions of inoculated plants, confirming Koch's postulates. No symptoms were observed on control plants. The host-parasite association of A. tuberosum and S. allii has been known only from China (1). S. alliacea has been recorded on several species of Allium, e.g. A. cepa, A. chinense, A. fistulosum, and A. tuberosum from Japan (4) and A. cepa from Korea (3). To the best of our knowledge, this is the first report of S. allii on garlic chives. No diseased plants were observed in commercial fields of garlic chives which involved regular application of fungicides. The disease therefore seems to be limited to organic garlic chive production.