Studies on bacterial biological control of powdery mildew and other fungal pathogens in Cornus florida
Cornus florida is an economically important ornamental tree native to the eastern part of North America. Tennessee is a major producer of the flowering dogwood which has been a source of income to many rural communities. Disease constraints that include powdery mildew significantly reduce plant growth and aesthetic value. The production necessitates routine preventive fungicide application which is expensive for small scale farmers. In addition, accidental exposure to chemical fungicides is toxic to human and animal populations, the environment, and also destroys natural microflora which consist of possible beneficial microbes. One endophytic and two epiphytic bacteria isolated from healthy flowering dogwoods displayed biological control activity against powdery mildew. The objective of this study was to identify and characterize the biological control agents and determine their effect on powdery mildew and other fungal pathogens affecting C. florida. Their mechanism of action was also explored. The biocontrol agents survived on temperatures up to 50 °C and were resistant to common fungicides used in prevention of powdery mildew in C. florida, salty conditions, select antibiotics, and pH levels. They also displayed varying amount of powdery mildew control in high and low disease pressure. The biocontrol agents showed antagonistic activity against other fungal pathogens that affect C. florida. The mechanisms of action observed are induced systemic resistance, antibiosis, competition, and parasitism. The biocontrol agents displayed growth promotion and increased plant vigor, increased enzyme activity, and pathogenesis related proteins significant at p<0.05. These bacterial biological control agents colonized C. florida leaves. The isolates colonized the powdery mildew spores and lysed it, yet other microbes on the leaf surface were not affected. Volatile secondary metabolites with antifungal and antibiotic activity were identified. Furthermore, non-volatile secondary metabolites including peroxidase, polyphenol oxidase and β-1,3- glucanase enzymes; as well as pathogenesis related proteins were increased due to the isolates treatment. These biological control agents will be beneficial as safer antifungal applications to be used solely, or as part of integrated disease management in C. florida.
"Studies on bacterial biological control of powdery mildew and other fungal pathogens in Cornus florida"
ETD Collection for Tennessee State University.