SPATIAL PATTERNS OF RHIZOPLANE POPULATIONS OF PSEUDOMONAS-FLUORESCENS

Geostatistical analysis was used to compare rhizoplane colonization pa tterns of an antibiotic-producing biological control bacterium versus a non-antibiotic-producing mutant strain. Pea seeds were inoculated wi th Pseudomonas flurorescens 2-79RN(10) or P. fluorescens 2-79-B46 (a p henazine-deficient Tn5 mutant of P. fluorescens 2-79RN(10)) (10(8) CFU /pea), planted in sterile sand, and incubated at 20 degrees C. After 3 days, seedlings were prepared for scanning electron microscopy. Photo micrographs (x 1,000) of the root surface were taken at the seed-root junction and at 0.5-cm intervals to the root tip. Bacterial counts on the root surface were made in 5- by 5-mu m sample units over an area w hich was 105 by 80 mu m. Coordinates and number of bacteria were recor ded for each sample unit. Spatial statistics were calculated by covari ance for the following directions: omnidirectional, 0, 45, 90, and 135 degrees. The ranges of spatial influence and nugget (estimator of spa tially dependent variation) were determined. For both P. fluorescens 2 -79RN(10) and P. fluorescens 2-79-B46, spatial structure was evident a long the entire root, particularly in the 0 degrees direction (along t he root length) (e.g., range = 24 mu m, nugget = 0.52). The degree of spatial dependence observed indicated aggregation of bacterial cells. No differences were detected in the spatial patterns of colonies of P. fluorescens 2-79RN(10) and P. fluorescens 2-79-B46, indicating that t he lack of phenazine production did not influence spatial patterns on the rhizoplane.