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Applied and Environmental Microbiology, July 2002, p. 3358-3365, Vol. 68, No. 7
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.7.3358-3365.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Seasonal Fluctuations and Long-Term Persistence of Pathogenic Populations of Agrobacterium spp. in Soils

Département de Foresterie, Faculté des Sciences, Université de Tlemcen, Tlemcen 13000, Algeria,¹ Institut des Sciences Végétales, CNRS, F-91198 Gif-sur-Yvette Cedex,² BBCE-IPM, UMR INRA 1088, F-21065 Dijon Cedex,,³ Ecologie Microbienne, Université Claude Bernard-Lyon 1, UMR CNRS 5557, and INRA, F-69622 Villeurbanne Cedex, France⁴

Received 6 February 2001/ Accepted 25 April 2002

Short- and long-term persistence of pathogenic (i.e., tumor forming) agrobacteria in soil was investigated in six nursery plots with a history of high crown gall incidence. No pathogenic Agrobacterium strains were isolated in soil samples taken in fall and winter in any plots, but such strains were isolated from both bulk soils and weed rhizospheres (over 0.5 x 10⁵ pathogenic CFU/g of bulk soil or rhizosphere) in three out of six plots in spring and summer. PCR amplifications of a vir sequence from DNA extracted from soil confirmed the presence of Ti plasmids in summer and their absence in fall and winter. The results indicate that strains that harbor a Ti plasmid had an unforeseen positive fitness versus Ti plasmid-free strains in soil and rhizosphere in spring and summer in spite of the apparent absence of tumor, and hence of opines. The gain of fitness occurred during a bloom of all cultivable agrobacteria observed only in conducive soils. An evolution of the pathogenic population was recorded during a 4-year period in one particularly conducive soil. In 1990, the pathogenic population in this soil consisted of only biovar 1 strains harboring both octopine- and nopaline-type Ti plasmids. In 1994, it consisted of only nopaline-type Ti plasmids equally distributed among biovar 1 and 2 strains. These results suggest that nopaline-type Ti plasmids conferred a better survival ability than octopine-type Ti plasmids to biovar 2 agrobacteria under the present field conditions.

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• Vogel, J., Normand, P., Thioulouse, J., Nesme, X., Grundmann, G. L. (2003). Relationship between Spatial and Genetic Distance in Agrobacterium spp. in 1 Cubic Centimeter of Soil. Appl. Environ. Microbiol. 69: 1482-1487 [Abstract] [Full Text]