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A Microbiological control of Melampsora medusae Thum. rust on Psuedotsuga menziesii (Mirb.) Franco seedlings McBride, Richard Phillips

Abstract

Saprophytic fungi and bacteria were recovered from healthy foliage of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco). The populations of microorganisms on foliage were variable and changed through the growing season. Three species of the bacteria isolated from Douglas fir foliage were used in attempts to control the development of the rust, Melampsora medusae Thum., on Douglas fir seedlings in the greenhouse. Effective control was obtained when Bacillus cereus Frankland and Frankland and B. mycoides Flugge were applied to the seedlings in pure cultures of nutrient broth. The most effective control was obtained from the application of a mixture of these two species and a third unidentified species of Baci1lus in nutrient broth. Less effective control resulted from the application of bacteria suspended in water and cell free filtrates of the bacterial cultures. The numbers of bacteria on the foliage of Douglas fir were estimated using a modification of the soil dilution and bacterial plate count technique. The bacterial populations on foliage of Douglas fir in the greenhouse and in the field were increased by the application of bacteria in nutrient broth and sterile nutrient broth.

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