FACTORS AFFECTING ATTACHMENT OF ENTEROBACTER-CLOACAE TO GERMINATING COTTON SEED

Attachment of Enterobacter cloacae EcCT-50,-a biological seed protecta nt used to control the seed-rotting fungi, Pythium ultimum-to cotton s eed was examined using conventional fluorescent microscopy (CFM), scan ning electron microscopy (SEM), and laser scanning microscopy (LSM). I n sand microcosms, E. cloacae quickly attached to the seed coat, with maximum attachment, 3 to 5 h after inoculation at 24 degrees C. In con trast, initial attachment of non-bacterized seed by Pythium ultimum wa s not observed until 6 h land not until 8 h on bacterized seeds). Comp arison of the movement of E. cloacae and P. ultimum in seed exudate gr adient semi-soft agar showed faster movement by the bacterium within t he first 6 h, and reduction of P. ultimum hyphal and germ tube growth in the presence of the bacterium, Microscopic observation of the seed coat revealed an early, intimate association, mediated, in part, by fi mbriae, and confirmed a loose association off. cloacae with the seed c oat previously reported. Spatially, the attached E. cloacae cells were distributed over the entire surface of the seed coat, but were especi ally abundant in the groves and near cracks where water imbibition and seed exudate release may occur. As the seed germinated and exposed va rious seed tissues, the bacterium rapidly attached to these tissues. A ttachment of the bacterium to the surface of intact germinating seeds, excised seed coat, polystyrene, and glass was 300, 110, 51, and <1 ce ll field(-1) 3 h(-1), respectively, suggesting that attachment is enha nced by seed germination. Attachment of E. cloncae to the seed coal wa s optimum in sands with high water concentrations, at temperatures of 18 to 30 degrees C, and at times that corresponded with optimum water imbibition during germination. Using several assays, attachment was sh own to be enhanced by seed exudate, and compounds such as methanol, fr uctose, and calcium. The results suggest that the release of certain n utrients and water imbibition during germination may play a role in th e rapid attachment to the seed by E. cloncae. The ability of E. cloaca e to rapidly move and attach to the seed coal may be related to its ab ility to function as a biocontrol agent.