Phenotypic Diversity in Lysobacter enzymogenes in Relations to Biological Control

Strains of the bacterium Lysobacter enzymogenes have been isolated from various regions of the world and reported to have potential as biological control agents against plant pathogens. Previous research revealed many ecological traits and mechanisms important to biological control by L. enzymogenes. Much of the previous research, however, was conducted on individual strains with little direct comparison of different strains. In this study, L. enzymogenes strains isolated from different locations and source materials (soil, roots, leaves) were compared for biocontrol-related phenotypic traits in vitro, epiphytic and endophytic colonization of leaves, and biocontrol of Bipolaris leaf spot on tall fescue. The ability to colonize leaves endophytically by L. enzymogenes was found for the first time in this study. The trait was shown to be common to all of the strains tested, with only subtle differences among strains in endophytic colonization ability. Endophytic colonization occurred after spray application of strains to bean, cabbage, Swiss chard and tall fescue, but not green onion. All of the strains tested exhibited similar ability to produce yeast cell-degrading enzymes, β-1, 3-glucanase, and antifungal secondary metabolites. Finally, all strains tested for control of Bipolaris leaf spot inhibited development of the disease, with only slight differences in levels of disease suppression among the strains. It can be concluded from the collective results that the ability to colonize leaves endophytically, the expression biocontrol-related traits, and the potential to have biological control activity are traits that are common to L. enzymogenes strains in general regardless of their origin. i Acknowledgements I would like to give my deepest appreciation to these who helped and supported me for the completion of my research. A special gratitude I give to my advisor Dr. Gary Yuen, who makes everything possible for me. He is the one that gave me the chance to stand here, and to live and spend the most wonderful three years in Lincoln. He is also the one that taught me how to do research, and the importance to keep my mind thinking. Words are not enough to express my thanks to him. I'm also thankful to one special person in our lab, Christy Jochum, who has been so helpful and supportive in my lab and greenhouse work. She made everything easier for me to access, and created a safe, happy, and organized research environment. Others I want to give my thanks to are members of my committee, Dr. Rhae Drijber …