Population Sizes, Immigration, and Growth of Epiphytic Bacteria on Leaves of Different Ages and Positions of Field-Grown Endive (Cichorium endivia var. latifolia)

Abstract

Total, fluorescent, and pectolytic epiphytic bacterial population sizes were quantified on leaves of different age groups of broad-leaved endive during field cultivation from leaf emergence until harvest. Greater bacterial population densities (log 10 CFU per square centimeter) were observed on outer leaves than on inner leaves of the plants throughout the growing season. These differences were statistically significant for total bacterial populations at all sampling times and were often significant for fluorescent and pectolytic bacterial populations. At harvest, a linear gradient of decreasing densities of epiphytic bacteria from outer (older) to inner (younger) leaves of the head was significant. Leaf age influenced the frequency distribution and variability of bacterial population sizes associated with leaves of broad-leaved endive. Total bacterial population sizes were greater at leaf emergence for leaves emerging during the second half of the cultivation period than for leaves emerging earlier. The size of fluorescent and pectolytic bacterial populations on newly emerged leaves increased throughout the season as plants aged. To assess the importance of plant age on bacterial immigration at leaf emergence, bacterial densities were quantified on leaves emerging simultaneously on plants of different ages. In two of the three experiments, greater bacterial population sizes were 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 adjacent leaves may act as a barrier for immigration of fluorescent bacteria on newly emerged leaves. Survival of an inoculated strain of Pseudomonas fluorescens on newly emerged leaves generally did not vary with the age of plants. However, these effects were not consistent among experiments, suggesting that interactions among micro-and macroenvironmental conditions, physiological condition of leaves, and accessibility of leaves to airborne bacteria are important in controlling epiphytic bacterial population sizes.

Development of Populations of Softrot Bacteria on Witloof Chicory Leaves during Root Production in the Field

“…The general pattern of the population changes as observed in this study was also found on broad-leaved endive studied by Jaques et al (1995). The plants acquired a microbial community early in the season and the plants kept their microbial communities although populations may have fluctuated during the season.…”

“…A study to identify the source of epiphytic softrot bacteria and whether it occurs by migration of growth of resident populations, has been performed by Jaques et al (1995). They showed that in the field the number of isolates of pectolytic bacteria does increase on the leaf surface of broad-leaved endive (Cichorium endivia var.…”

“…species, Erwinia carotovora ssp, carotovora (Jones) Bergey etal, 1923 (Ecc) 1925 (Pm). These bacteria are not only plant pathogens but also saprophytes on plant surfaces and in the soil (Jaques et al,. 1995;van Outryve etal,, 1989), As symptoms of bacterial softrot have never been observed during the 4 years of our field experiments, the bacteria apparently survive as saprophytes or in latent infections on the crop.…”

Measurement of wet deposition of inorganic and organic nitrogen in a forest environment

“…The fluctuations in stability indicate that there are factors, both internal and external to the sample bottles, influencing the stability of the rainwater samples, such as bacterial concentrations in the rain or on the canopy, variations in temperature, and chemical reactions. Many different kinds of bacteria can be found in the air, in rain, in clouds [ Bauer et al , 2002, and references therein], and on nearly all surfaces near and on the ground [e.g., Jacques et al , 1995]. Nitrifying bacteria that convert ammonium to nitrate have been shown to be present in appreciable numbers on leaf surfaces and inside stomatal cavities [ Papen et al , 2002] and can wash off the leaves as throughfall, thereby being collected and allowed to process nitrogen in the rain sample.…”

Temporal fluctuations in the pseudomonad population associated with sugar beet leaves

“…For example, understanding the dynamics of populations will aid in the development of more persistent and e¡ective inocula [18]. The unpredictable survival of bacteria on plants observed in release studies [18,44] may be attributed to variable plant and weather conditions which a¡ect the relative ¢tness of the released organism. A single strain selected for the desired characteristics such as invasion and exclusion ability [45] under one set of conditions is unlikely to perform e¡ectively in all ¢eld conditions.…”