First report of crown gall, caused by Agrobacterium tumefaciens on Geraldton wax (Chamelaucium unicinatum) in South Africa

Geraldton wax (Chamelaucium uncinatum, family Myrtaceae) plants are grown as cutflowers for the export market in South Africa. In July 1998, gall-like structures were observed on collars and roots of Geraldton wax plants in commercial fields in Wellington. The galls were observed after plants exhibited poor growth. The galls varied in size and in texture from soft and spongy to hard. Secondary symptoms involved poor root development and browning of stem tissues near galls. Isolations from the galls yielded nearly pure cultures of a Gram negative, rod-shaped bacterium on Roy Sauer medium (2), typical of an Agrobacterium sp. Carbon source utilization testing with the Biolog GN Bacterial Identification System (version 3.50) confirmed the bacterium as a biovar of A. tumefaciens with a similarity of 0.88. Pathogenicity was confirmed by injecting 4- to 6-week old tomato and tobacco plants and 1-year-old Geraldton wax plants with approximately 5 μl of the bacterial suspension (10 CFU/ml) in sterile, distilled water. Inoculated plants were then transferred to a greenhouse at 25°C. Galls developed 1 month after inoculation. The bacterium was readily reisolated from the inoculated plants. A. tumefaciens is endemic to South Africa and has a very wide host range that includes several ornamentals (1). This is the first report of A. tumefaciens on Geraldton wax plants in South Africa. References: (1) J. F. Bradbury. 1986. Guide to Plant Pathogenic Bacteria. CAB Int., Slough, U.K. (2) N. W. Schaad. 1988. Laboratory Guide for Identification of Plant Pathogenic Bacteria. The American Phytopathological Society, St. Paul, MN.