DISPERSAL OF WILD-TYPE AND GENETICALLY-MODIFIED PSEUDOMONAS SPP FROM TREATED SEEDS OR SOIL TO AERIAL PARTS OF RADISH PLANTS

Dispersal of wild-type and genetically-modified strains of plant growt h-promoting fluorescent Pseudomonas spp to aerial parts of radish plan ts was investigated using different inoculation strategies. P. putida strain WCS358rr colonized the surface of cotyledons of radish plants w hen seeds were coated with this strain or when non-coated seeds were s own in soil treated with WCS358rr. The cotyledons were not colonized b y WCS358rr when suspensions of this strain were inoculated onto roots of radish seedlings that had already grown for 4 d in soil. Strain WCS 358rr not only colonized the surface, but also the interior of cotyled ons. For all types of inoculation strategies tested, strain WCS358rr c olonized the root surface but did not penetrate the interior of the ro ot. These results indicate that WCS358rr was not transported up, or do wnwards through the vascular system. When coated on seed, dispersal to cotyledons of radish was also demonstrated for P. fluorescens WCS374 and its genetically-modified derivative WCS374pMR. Plasmid pMR was mai ntained in WCS374pMR throughout the experiment. No differences were ob served between modified strain WCS374pMR and wild-type strain WCS374 w ith regard to dispersal to and colonization of cotyledons and roots of radish. Strains WCS358rr, WCS374 and WCS374pMR survived on cotyledons for a period of 21-31 d. Dispersal of the applied bacterial strains t o the first true leaves of radish could not be demonstrated. The resul ts indicate that cotyledons of radish become contaminated with strains of Pseudomonas spp during germination of treated seeds or during seed ling emergence from treated soil. The implications of dispersal of wil d-type and genetically-modified pseudomonads to aerial parts of the pl ant are discussed.