GENETIC AND ECOTYPIC STRUCTURE OF A FLUORESCENT PSEUDOMONAS POPULATION

Fluorescent pseudomonads are among the most numerous bacteria found on plant surfaces and the activity of certain isolates can affect plant growth. In 1993, 108 fluorescent Pseudomonas isolates were collected o n a single sampling occasion from the leaves of sugar beet plants grow n at the Oxford University Field Station, Wytham. Isolates were obtain ed from 54 different leaves, from nine plants, and characterized using 10 allozyme and 23 biotype markers. Statistical analysis of the combi ned data revealed five biotypic traits which permitted a rational clas sification of the sample. Analysis of the allozyme data showed that th e population was in overall linkage disequilibrium. Clonality was also observed after subdivision of allozyme data along spatial and habitat levels. However, two genetically defined subgroups were in linkage eq uilibrium which suggests the possibility of frequent large-scale recom bination among certain isolates. A significant correlation between iso late distribution and habitat (leaf type and plot) indicates that the population has ecotypic structure.