Disease Note

Alternaria raphani, on Turnip in Arizona. P. J. Cotty and S. M. Alcorn, Department of Plant Pathology, University of Arizona, Tucson 85721. Plant Disease 68:732, 1984. Accepted for publication 2 May 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-732c.

Arizona crucifer crops (broccoli, turnip, rapini, radish, cauliflower) were valued at over $20 million in 1982.  A significant portion of these are seed crops for which seed contamination with Alternaria spp. is a concern.  During the fall of 1982, severe leaf spotting occurred in turnip fields in the Phoenix area.  Alternaria raphani Groves & Skolko, known to colonize crucifer seeds in North America, was isolated from the lesions and was pathogenic to broccoli (Brassica oleracea L. var. botrytis L., cv. Italian green sprouting calabrese) and turnip (B. rapa L.), cv. Burpee No. 6121).  Conidia and chlamydospores characteristic of the species were produced in culture (5% V-8 juice, 2% agar, 12-hr diurnal cycle of 5,500 lux fluorescent light).  This is the first report of this pathogen in Arizona.  A similar outbreak on turnip was reported from India.

References: Narain, U., and Saksena, H. K. Indian Phytopathol. 28:98, 1975.  Petrie, G. A. Can. Plant Dis. Surv. 58:99, 1978.