A study was made of 30 Agrobacterium tumefaciens isolates obtained from diseased rose plants from France, Spain and Morocco. It revealed for the first time that the exponential spread of crown gall disease in Mediterranean rose cultivation is due the following factors: the vegetative propagation of rootstocks; the frequent exchange of plant material between professional breeders and propagators; the increasing turnover rates for flower production. Because an efficient chemical or genetic control of the disease will not be available in the near future, further propagation of disease can be reduced only through selection of healthy rootstocks. Sensitive tests for detection and identification of the disease have been developed. C. Poncet, G. Bonnet, S. Pionnat, D. Hericher, and A. Bettachini. ISHS Acta Horticulturae 547: III International Symposium on Rose Research and Cultivation. www.actahort.org