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Plant Pathology Circular No. 220, January 1980
Fla. Dept. Agric. & Consumer Services
Division of Plant Industry
J. W. Miller
Christmas cactus, Zygocactus truncatus Schum., is grown commercially in Florida as potted plants and hanging baskets for their showy blossoms which form around Christmas time. The plants are commonly propagated by rooting sections of the flat, jointed stems, called phylloclades.
Fusarium oxysporum (Schlecht.) emend. Snyd. et Hans. was isolated from Christmas cacti which showed a water-soaked rot at the soil line and spots on the phylloclades. Reproduction of the symptoms by inoculating healthy plants with the fungus proved it to be the cause of the disease (2).
SYMPTOMS. Established plants and cuttings develop a water-soaked rot which usually begins at the soil line and which frequently has a red border. Abscission of the phylloclades above the infection occurs in both cuttings and plants (Fig. 1A). Spots on the phylloclades vary from orange, sunken lesions to circular reddish spots with sunken gray centers (2) (Fig. 1B).
CONTROL. Use of pathogen-free plants, sterilized soil, and early roguing of any infected plant is recommended.
Reference to University of Florida/IFAS Pest Control Guides
Fig. 1A, and Fig. 1B. (94K)
Fig.1A Fusarium oxysporum on Zygocactus truncatus.
Abscission of phylloclades following infection by the fungus.
Fig.1B. Sunken orange spots and circular lesions with gray
centers and reddish margins. (DPI Photo #680830)
SURVEY AND DETECTION. Look for abscised phylloclades, then for water-soaked lesions, occasionally with red borders at or near the soil line. These symptoms are similar to those caused by Phytophthora parasitica Dast. (1), but Fusarium also causes orange to reddish leaf spots which are not associated with Phytophthora. It can occur any time of the year.
Contribution No. 500, Bureau of Plant Pathology, P. O. Box 1269, Gainesville, FL 32602.
LITERATURE CITED.
1. ALFIERI, S. A., JR., and J. W. MILLER. 1977. Christmas cactus: basal stem and root rot. Fla. Dept. Agric. & Consumer Serv., Div. Plant Ind., Plant Pathol. Circ. No. 174. 2p.
2. MILLER, J. W. 1975. Blight and leaf spot of Christmas cactus caused by Fusarium oxysporum. (Abstr.) Proc. Amer. Phytopathol. Soc. 2:162.
