Circular 174

Christmas Cactus: Basal Stem and Root Rot

Plant Pathology Circular No. 174, January 1977
Fla. Dept. Agric. & Consumer Services
Division of Plant Industry

S. A. Alfieri, Jr., and J. W. Miller

Christmas cactus, Zygocactus truncatus Schum., is grown as a potted ornamental, primarily for its showy flowers which occur in a variety of colors. Its stems lack spines characteristic of the cactus family and its segments (phylloclades) lend themselves readily to vegetative propagation. As a foliage plant, it represents the greatest portion of the $1.3 million annual sales of cacti in Florida (Dr. C. N. Smith, personal communication).

Phytophthora parasitica Dast. is the causal fungus of basal stem and root rot of Christmas cactus (1,3). It is one of the most destructive plant pathogens, attacking 72 genera in 42 families of flowering plants (4). P. parasitica is primarily a soil-borne pathogen affecting roots and crowns; however, it potentially is a serious foliage blighting fungus (2,3).

Fig. 1. Infection of Christmas cactus by Phytophthora parasitica, showing A) initial water-soaked spots on basal stem segment, B) advanced necrosis of basal stem segment with reddish brown margin, and C) abscission of terminal stem segments, lying on soil surface of pot.

SYMPTOMS.

Stems of diseased plants appear lifeless, having a dull, grey-green color, and droop much more severely than the gracefully arched healthy stems. Following basal stem infection, 2 or 3 of the terminal segments may abscise. The basal stem rot, occurring at or just below the soil line, is water-soaked, rather firm, and frequently delimited by a wavy, faded reddish margin (fig. 1). Infected roots are brown, soft, water-soaked, and necrotic.

CONTROL.

Effective control of this disease lies in the use of pasteurized soil, the prevention of soil infestation by the fungus.

Reference to University of Florida/IFAS Pest Control Guides

Contribution No. 426, Bureau of Plant Pathology, P. O. Box 1269, Gainesville, FL 32602.

Literature Cited

1. Alfieri, S. A., Jr., and J. W. Miller. 1970. A new disease of Christmas cactus (Zygocactus truncatus) in Florida. Phytopathology 60:1281. (Abstr.)

2.__________. 1970. Bougainvillea blight, a new disease caused by Phytophthora parasitica. Phytopathology 60:1806-1808.

3.__________, and J. W. Miller. 1971. Basal stem and root rot of Christmas cactus caused by Phytophthora parasitica. Phytopathology 61:804-806.

4. Hickman, C. T. 1958. Phytophthora plant destroyer. Trans. Brit. Mycol. Soc. 41:1-13.

5. Knauss, J. F. 1975. Control of basal stem and root rot of Christmas cactus caused by Pythium aphanidermatum and Phytophthora parasitica. Proc. Fla. State Hort. Soc. 88:567-571