Characterization of agrobacteria from weeping fig (Ficus benjamina)

Ficus benjamina plants, galled both at epi- and hypogeous parts, were obser ved in Italy and in The Netherlands, and these were the first records of th e appearance of weeping fig crown gall in Europe. A total of 241 Agrobacter ium isolates was obtained from 41 tumours and studied for their morphologic al, physiological and phytopathological characters. Two main groups of agro bacteria were distinguished by their colony morphology and through classica l biovarietal tests that allowed allocation of 86 isolates into biovar 1 an d 155 into an intermediate biovar rather different from any of the three bi ovars defined for agrobacteria. Most of the isolates were unable to utilize mannopine, nopaline or octopine as C and N sources; only 62 strains utiliz ed nopaline. However, when nonopine-utilizing strains were inoculated into F. benjamina, only nopaline was detected in the developing tumours. BIOLOG ML 1(TM) system analysis applied to 50 representative strains allowed ident ification of the biovar 1 isolates as Agrobacterium tumefaciens and most of the intermediate biovar isolates as the newly proposed species Agrobacteri um fici. Analysis of sensitivity to a set of 14 antibiotics confirmed the a llocation of the 50 strains into two well defined main clusters matching th e BIOLOG identification. Out of 141 tumorigenic isolates, 66 were sensitive in vitro to agrocine 84, but four of these strains showed scarce or no sen sitivity to the antagonist A. radiobacter K84 when tested in fig plants. Th e two types of agrobacteria could usually be isolated from the same tumours . Tumorigenic strains were able to induce tumours in six herbaceous plant s pecies, in eight to 10 out of 12 woody plants and in six to eight out of ni ne Ficus species, indicating a wide host-range Ti plasmid. Agrobacteria wer e able to survive and move in the vascular system of galled ficus plants an d to induce tumour growth in stem-cutting propagated plants. Moreover, agro bacteria were detected in many healthy F. benjamina plants as part of the e ndophytic microflora. These findings suggest potential for spread of the di sease through latently infected plant propagation material produced as cutt ings or by tissue culture.