A polyphasic taxonomic study was performed on 16 Stenotrophomonas strains from environmental and clinical sources. A group of three plant-associated isolates were shown to be phenotypically different from the other strains. This group formed a separate physiological cluster (B1) with 42 % heterogeneity to the other isolates. The defining characteristics of the new species were as follows : growth at 4 mC and the absence of growth at 40 mC ; the utilization of xylose as a carbon source ; lower osmolytic tolerance ( 4 5 % NaCl, w/v), although the isolates can produce trehalose and glucosylglycerol as osmoprotective substances ; the absence of lipase and β-glucosidase production ; and antifungal activity against plant-pathogenic fungi. The wholecell fatty acid profile of this group was different and characterized by the main fatty acids iso-C 15 :0 and anteiso-C 15 :0 . Numerical analysis of the fatty acid profiles of the strains examined supports the differentiation of the physiological B1 group. By 16S rDNA analysis, three clusters were distinguished. The three strains of the B1 group formed a separate environmental cluster (E1). They showed a mean similarity of 99 5 % within the cluster, and differed from strains of a second environmental cluster (E2) by 2 2 % and from the clinical cluster (C) by about 3 0 %. DNA-DNA hybridization data supported the taxonomic differentiation. All results led to the proposal of a new species, Stenotrophomonas rhizophila sp. nov., with strain e-p10 T

Aims: A screening approach was developed to assess the potential of rhizobacterial strains to control Verticillium wilt caused by Verticillium dahliae Kleb. Methods and Results: Sixty randomly chosen antagonistic bacterial strains originally isolated from rhizosphere of three different host plants of V. dahliae ± strawberry, potato and oilseed rape ± were evaluated for biocontrol and plant growth promotion by analysing in vitro antagonism towards V. dahliae and other plant pathogenic fungi, production of fungal cell walldegrading enzymes and plant growth-promoting effects on strawberry seedlings. To test the plant growth-promoting effect, a microplate assay with strawberry seedlings was developed. Although the rhizobacterial strains were isolated from different plants they showed effects on the growth of strawberry seedlings. According to the in vitro biocontrol and plant growthpromoting activity, the three best candidates Pseudomonas putida B E2 (strawberry rhizosphere), Ps. chlororaphis K15 (potato rhizosphere) and Serratia plymuthica R12 (oilseed rape rhizosphere) were selected for greenhouse experiments to verify the in vitro screening results. Under greenhouse conditions the isolates selected according to this strategy were as effective, or more effective than commercial biocontrol agents and may therefore possibly be valuable as antagonists of V. dahliae. Conclusions: In this study, the screening strategy resulted in a selection of three interesting biocontrol candidates against Verticillium: Ps. putida B E2 (strawberry rhizosphere), Ps. chlororaphis K15 (potato rhizosphere) and Ser. plymuthica R12 (oilseed rape rhizosphere). Signi®cance and Impact of the Study: A new combination of in vitro screening methods including a microplate assay with strawberry seedlings to test the plant growth promoting effect which allow to more ef®ciently select potential biological control agents was developed successfully.