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Red Mustard, Tah Tsai, and Japanese Mustard as Hosts of Pseudo-cercosporella capsellae in California. S. T. Koike, University of California Cooperative Extension, Salinas 93901. Plant Dis. 80:960. Accepted for publication 28 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0960B.

In California, the leafy crucifers Japanese mustard (Brassica campeslris L. subsp, nipposinica), red mustard (Brassica juncea (L.) Czernj. & Coss. subsp, rugosa), and tah tsai (Brassica campeslris L. subsp, nari-nosa) are grown in adjacent rows and harvested for use in packaged salad mixes. In the spring seasons (January to April) of 1995 and 1996, a foliar disease reduced marketability of red mustard and tah tsai crops grown in coastal counties. Circular, light tan to off-white leaf spots measuring 2 to 6 and 2 to 8 mm in diameter were observed on red mustard and tah tsai, respectively. White sporulation was common on both hosts, and the hyaline, cylindrical conidia from red mustard and tah tsai isolates measured 60.3 to 70.8 x 2.8 to 3.3 µm and 68.1 to 79.7 x 1.5 to 2.0 µm, respectively. Isolations on acidified potato dextrose agar (PDA) (2 ml of 25% lactic acid per liter) yielded slow-growing, raised, black, stromatic colonies that produced few conidia. On 2% water agar, colonies were similar to those on PDA, but also released a purple-pink pigment into the media. The pathogen on both hosts was identified as Pseudocercosporella capsellae (Ellis & Everh.) Deighton (1,2). Isolates from red mustard and tah tsai were cultured on V8 agar for 21 days under a 12 h light/12 h dark cycle, macerated in sterile distilled water with a tissue homogenizer, fil tered through cheesecloth, and sprayed onto 4-week-old seedlings of red mustard cv. Red Giant, tah tsai cv. Tokita, Japanese mustard cv. Mizuna, broccoli (B. oleracea L. subsp, italica cv. Greenbelt), and Chinese cabbage (B. campeslris L. subsp, pekinensis cv. Cha-Cha). Plants were incubated in a moist chamber for 48 h and then maintained in a greenhouse. After 10 days, leaf spots similar to those originally observed developed on all plants inoculated with either isolate. Conidia of P. capsellae developed on the leaf spots, and isolations resulted in colonies morphologically similar to the original cultures. Control plants sprayed with distilled water remained symptomless. The experiment was repeated, and the results were similar. For California, this is the first report of while leaf spot caused by P. capsellae on commercially-grown red mustard and tah tsai and also the first report of Japanese mustard as a host of the same pathogen.

References. (1) A. J. Inman el al. Mycol. Res. 95:1334, 1991. (2) G. A. Petrie and T. C. Vanterpool. Can. Plant Dis. Surv. 58:69, 1978.