Biological control of powdery mildew on Cornus florida using endophytic Bacillus thuringiensis

Powdery mildew (Erysiphe pulchra) is a devastating disease in nursery production of flowering dogwood (Cornus florida L.). Disease management relies heavily on season-long use of chemical fungicides and there is a demand for alternative strategies. An endophytic bacterium IMC8 was isolated from disease-free C. florida stem tissue, and was shown to be an effective biological control agent against E. pulchra in growth chamber, greenhouse and shadehouse environments. This isolate, identified as Bacillus thuringiensis, exhibited normal growth in NaCl concentrations up to 6%, pH 5 to 11, and temperatures up to 50 degrees C. It was compatible with the conventional fungicide thiophanate methyl and clarified hydrophobic extract of neem seed oil at label recommended concentrations. The isolate IMC8 produced volatile compounds identified by GC/MS, which included antifungal and antibacterial compounds and suggested antibiosis as a mode of action. Scanning electron microscopy revealed lysis of powdery mildew spores and hyphae, which suggested parasitism as a second mode of action. These observations suggested that the isolate IMC8 has potential as a biological control agent in the management of powdery mildew on C. florida, and would tolerate a wide range of salinity, pH and high temperature conditions. It could be included as a component of integrated pest management in rotation or tank mix with lower levels of conventional fungicides, or used with clarified hydrophobic extract of neem seed oil.