At 5-year intervals, beginning in 1970, international symposia have been organized to provide a forum for discussions on phyllosphere microbiology (1970, Newcastle-upon Tyne, England 1975, Leeds, England 1980, Aberdeen, Scotland 1985, Wageningen, The Netherlands, 1990, Madison, Wisconsin 1995, Bandol, France 2000, Berkeley, California). Since then, a relatively small but devoted band of scientists has worked diligently to explore the microbiology of leaves. Indeed, Ruinen's research focused on the possible colonization of leaves of plants in the tropics (Indonesia and Surinam) by Beijerinckia and other nitrogen-fixing bacteria. Interest in leaves as habitats for microorganisms, not merely the causal agents of disease, has grown since the midcentury. Phytopathogenic microbes and the economic impact of diseases on crop production continue to provide a major motivation for research on the phyllosphere as an ecosystem. Up to that time, interest in leaves and their microbial inhabitants was largely centered on diseased leaves and the microbes that caused the various foliar diseases. Ruinen published a paper entitled “The Phyllosphere-an Ecologically Neglected Milieu” ( 249). Then multiply this by the almost infinite number of individual trees and other plants present on our planet, and the diversity of habitats that these leaves provide leads to an appreciation of the enormity and importance of leaf-microbe ecosystems.
Then think of each of these leaves as a habitat for 1 to 10 million bacteria. When you view a tree (or any plant), think of it as a support system for 1,000 leaves. Colonization of leaves by microbes is not limited to terrestrial plants but includes aquatic plants as well ( 90). Each leaf, in turn, may be inhabited by a qualitatively and quantitatively diverse assemblage of microorganisms, including fungi, yeasts, bacteria, and bacteriophages (cf. Plants cover a significant proportion of the global land area. syringae-leaf ecosystem is a particularly attractive system with which to bridge the gap between what is known about the molecular biology of genes linked to pathogenicity and the ecology and epidemiology of associated diseases as they occur in natural settings, the field. While still in their infancy, such research efforts demonstrate that the P. A number of genes and traits have been identified that contribute to the fitness of P. The bacterium can be found in association with healthy leaves, growing and surviving for many generations on the surfaces of leaves as an epiphyte. However, disease causation is but one aspect of its life strategy. syringae was first studied for its ability to cause disease on plants. Many of these factors influence the development of populations of P. The physical and physiological characteristics of leaves change as they expand, mature, and senesce and as host phenology changes. Seasonal climatic changes impose still a longer cycle. Slightly longer-term changes occur as weather systems pass. The physical environment surrounding phyllosphere microbes changes continuously with daily cycles in temperature, radiation, relative humidity, wind velocity, and leaf wetness. Leaf ecosystems are dynamic and ephemeral. syringae to illustrate the attractiveness and somewhat unique opportunities provided by leaf ecosystems for addressing fundamental questions of microbial population dynamics and mechanisms of plant-bacterium interactions. syringae) to be deliberately introduced into the environment. syringae, as it gained notoriety for being the first recombinant organism (Ice − P. Among the diversity of bacteria that colonize leaves, none has received wider attention than P. This review focuses on the bacterial component of leaf microbial communities, with emphasis on Pseudomonas syringae-a species that participates in leaf ecosystems as a pathogen, ice nucleus, and epiphyte. The timestamp is only as accurate as the clock in the camera, and it may be completely wrong.The extremely large number of leaves produced by terrestrial and aquatic plants provide habitats for colonization by a diversity of microorganisms. If the file has been modified from its original state, some details such as the timestamp may not fully reflect those of the original file.
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