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Disease Note.

First Report of Phytophthora Rot of Cabbage Caused by Phytophthora porri Foister in Wisconsin. M. F. Heimann, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 78:1123. Accepted for publication 5 August 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1123A.

A cabbage head, Brassica oleracea L. var. capitata, harvested in October of 1992 and stored at 33-35 F (0.5-1.5 C), was submitted to the Plant Pathogen Detection Clinic of the Department of Plant Pathology, University of Wisconsin, in February 1993. The cabbage sample was the cultivar Hinova, but the grower said disease incidence was not limited to this cultivar. He observed that there was an approximate 5% yield loss due to this disease. Disease symptoms consisted of blackish brown wrapper leaves and a brown internal wet rot. The pith of the stalk was rotted and exhibited a chambered pattern; i.e., the pith was absent except for a network of tissue that created a large cell-like pattern. Soft rotting bacteria were present causing the typical odor of rotting brassicas. (These bacteria produce pitting on Crystal Violet Pectate medium.) Phytophthora oospores were found in the decayed tissues. The fungus was identified as Phytophthora porri Foister after being grown on various selective media such as PAR (2), carrot agar, and cabbage agar. Some of the identifying characters of P. porri were coiled hyphae with swellings of round, angular, or ellipsoidal shapes. Sporangiophores had intercalary swellings. Oogonia had paragynous and amphigynous antheridia. Measurements of the various structures were in keeping with those described for P. porri in CMI Description of Pathogenic Fungi and Bacteria No. 595. Koch's postulates were carried out twice successfully. Healthy cabbage heads of an unknown cultivar were procured from a local market. A hole was made in the pith with a sterile cork borer, and a mycelial plug was pushed into this hole. The fungus subsequently ramified throughout the pith and into the head tissue causing breakdown. P. porri was recovered and identified. This fungus was reported on carrot in Canada (1). This is the first report of it on cabbage in Wisconsin and in the United States to the extent of the author's knowledge. It has been reported on cabbage in Norway, the Netherlands, and the United Kingdom.

References: (1) H. H. Ho, Mycologia 75:747, 1983. (2) M. E. Kannwischer and D. J. Mitchell, Phytopathology 68:1760, 1978.