In April 2011, commercial garlic (Allium sativum) in Monterey County, CA showed symptoms of an undocumented disease. Bulb and stem sheaths were dark, decayed, and sloughing off the plants. Dissection of diseased sheaths revealed black hyphae between layers. Lower leaves wilted, turned tan, and dried up. Disease occurred in small patches scattered in two fields. In the patches, disease incidence was as much as 50%; however, overall field incidence was less than 1%. Isolations from 80% (16 of 20 plants) of collected plants resulted in the recovery of a dark olivaceous black fungus. Conidiophores were geniculate and brown and conidia were borne singly, brown, and ellipsoidal to cylindrical. Conidia had two to five but mostly three transverse septa. Longitudinal septa were infrequent and apical cells were rounded. Conidia measured (19.0-) 26.3 to 36.6 (-42.8) × (6.7-) 9.2 to 9.9 (-12.9) μm. Dark, intercalary chlamydospores were observed as colonies aged. DNA sequencing of the internal transcribed spacer (ITS) regions of four, single-spored isolates was completed with primers ITS1 and ITS4 (3). Sequences of all isolates (GenBank Nos. JN588614 to JN588617) were identical and 100% similar to Embellisia allii (AY278840). On the basis of morphological and molecular data, the fungus was identified as E. allii (Campanile) Simmons (1). Pathogenicity of four of the sequenced E. allii isolates and one additional E. allii isolate was tested using inoculum grown on acidified potato dextrose agar and garlic (cv. California Late) planted into 15-cm pots. A transverse incision was made at a point 2 cm above the garlic bulb so that a colonized agar plug could be inserted between the second and third sheath layer. The stem was then wrapped with Parafilm. Ten plants per isolate were inoculated and kept in a greenhouse (24 to 26°C). Seven to eight days after inoculation, the tissue around the incision turned tan and dark fungal growth was observed. Fourteen days after inoculation, the inoculated area was necrotic and dark fungal growth developed between stem layers. E. allii was reisolated from all inoculated plants and matched the morphological characteristics of the original isolates. Control plants, inoculated with uncolonized agar plugs, developed no symptoms. This experiment was repeated with similar results. In addition, one isolate was used to inoculate leek (A. porrum cv. Lancelot) and onion (A. cepa cv. Evergreen). Similar symptoms developed on these two species and E. allii was reisolated from all plants. To our knowledge, this is the first documentation of skin blotch and bulb canker caused by E. allii on garlic in California. Affected plants were of poor quality and could not be harvested. Our findings that garlic isolates of E. allii can infect leek and onion provide preliminary evidence that this pathogen is not restricted to garlic; this information may be useful to growers when considering crop rotations. E. allii has been reported on garlic in a number of places in Africa, Asia, Europe, the Middle East, and North and South America (2). The sequenced E. allii isolates are deposited in the fungal collection at the CDFA Plant Pest Diagnostics Lab (CDFA798-801).
References: (1) J. C. David. Mycopathologia 116:59, 1991. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/, August 8, 2011, (3) B. M. Pryor and D. M. Bigelow. Mycologia 95:1141, 2003.