Basal Stem Canker of Poinsettia Caused by Fusarium solani in Wisconsin. M. F. Heimann, Department of Plant Pathology, University of Wisconsin, Madison 53706. G. L. Worf, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 71:469. Accepted for publication 19 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0469B.
Poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants with stem cankers were noted in Wisconsin in December 1985. Cankers were most often in the basal portion of the stem, usually about 2 cm above the soil line and 3-6 cm long. Cankers were never contiguous with the soil line of the stem, and external mycelium was not observed. Lesions were brown to black and somewhat shrunken, with distinct necrotic margins and structural discoloration that often extended beyond the canker margins. Phloem, cambium, and xylem, but not pith tissues, were affected. Sometimes the bark tissue was shredded. The grower reported that cankers became evident sometime after potting but that plants developed normally during the growing season; some plants wilted on retail shelves, probably after stress. Fusarium solani (Mart.) Sacco was isolated consistently from the cankers; identification was later confirmed by P. Nelson (personal communication). Ten coated cuttings each of cultivars Annette Hegg, Lady, and Top White were inoculated through puncture wounds, sealed with Vaseline, and maintained at 20 C; whether puncturing was necessary was not determined. All inoculated plants had typical symptoms and cankers 20 days later; wound controls remained symptomless. F. solani was reisolated, confirming pathogenicity.