POPULATION SIZES, IMMIGRATION, AND GROWTH OF EPIPHYTIC BACTERIA ON LEAVES OF DIFFERENT AGES AND POSITIONS OF FIELD-GROWN ENDIVE (CICHORIUM-ENDIVIA VAR LATIFOLIA)

Total, fluorescent, and pectolytic epiphytic bacterial population size s were quantified on leaves of different age groups of broad-leaved en dive during field cultivation from leaf emergence until harvest, Great er bacterial population densities (log(10) CPU per square centimeter) were observed on outer leaves than on inner leaves of the plants throu ghout the growing season, These differences were statistically signifi cant for total bacterial populations at all sampling times and were of ten significant for fluorescent and pectolytic bacterial populations. At harvest, a linear gradient of decreasing densities of epiphytic bac teria from outer (older) to inner (younger) leaves of the head was sig nificant, Leaf age influenced the frequency distribution and variabili ty of bacterial population sizes associated with leaves of broad-leave d endive. Total bacterial population sizes were greater at leaf emerge nce for leaves emerging during the second half of the cultivation peri od than for leaves emerging earlier. The size of fluorescent and pecto lytic bacterial populations on newly emerged leaves increased througho ut the season as plants aged, To assess the importance of plant age on bacterial immigration at leaf emergence, bacterial densities were qua ntified on leaves emerging simultaneously on plants of different ages, In two of the three experiments, greater bacterial population sizes w ere observed on leaves emerging on younger plants, This indicates that factors other than an increase in concentration of airborne bacteria can lead to increases in population sizes at leaf emergence as plants age in the field. Results of leaf pruning experiments suggested that a djacent leaves may act as a barrier for immigration of fluorescent bac teria on newly emerged leaves, Survival of an inoculated strain of Pse udomonas fluorescens on newly emerged leaves generally did not vary wi th the age of plants, However, these effects were not consistent among experiments, suggesting that interactions among micro- and macroenvir onmental conditions, physiological condition of leaves, and accessibil ity of leaves to airborne bacteria are important in controlling epiphy tic bacterial population sizes.