EFFECT OF 2 PLANT-SPECIES, FLAX (LINUM-USITATISSINUM L) AND TOMATO (LYCOPERSICON-ESCULENTUM MILL), ON THE DIVERSITY OF SOILBORNE POPULATIONS OF FLUORESCENT PSEUDOMONADS

Suppression of soilborne disease by fluorescent pseudomonads may be in consistent, Inefficient root colonization by the introduced bacteria i s often responsible for this inconsistency, To better understand the b acterial traits involved in root colonization, the effect of two plant species, flax (Linum usitatissinum L.) and tomato (Lycopersicon escul entum Mill.), on the diversity of soilborne populations was assessed, Fluorescent pseudomonads were isolated from an uncultivated soil and f rom rhizosphere, rhizoplane, and root tissue of flax and tomato cultiv ated in the same soil. Species and biovars were identified by classica l biochemical and physiological tests, The ability of bacterial isolat es to assimilate 147 different organic compounds and to show three dif ferent enzyme activities was assessed to determine their intraspecific phenotypic diversity, Numerical analysis of these characteristics all owed the clustering of isolates showing a high level (87.8%) of simila rity. On the whole, the populations isolated from soil were different from those isolated from plants,vith respect to their phenotypic chara cteristics. The difference in bacteria isolated from uncultivated soil and from root tissue of flax was particularly marked, The intensity o f plant selection was more strongly expressed with flax than with toma to plants, The selection was, at least partly, plant specific. The use of 10 different substrates allowed us to discriminate between flax an d tomato isolates, Pseudomonas fluorescens biovars II, III, and V and Pseudomonas putida biovar A and intermediate type were well distribute d among the isolates from soil, rhizosphere, and rhizoplane, Most isol ates from root tissue of flax and tomato belonged to P. putida by. A a nd to P. fluorescens by. II, respectively, Phenotypic characterization of bacterial isolates was well correlated with genotypic characteriza tion based on repetitive extragenic palindromic PCR fingerprinting.