EFFECT OF SREPTOMYCIN SPRAYS ON LEAF MICROFLORA ON PEAR TREES
The control of bacterial plant diseases by the antibiotics is forbidden in France, however the use of streptomycin is suggested for the control of Fire blight. To measure the selection pressure of this antibiotic against leaf microflora, we sprayed 200 μg/ml of streptomycin sulfate, weekly, on pear cv. Passe-Crassane during the period of 27 July to 10 October 1982. Bacteriological analysis were made at monthly intervals. Following first month of sprays, the total bacterial population of treated samples was found to be one-tenth of the unsprayed check. After two and three months of spraying, the antibiotic does not have a cumulative effect on the bacterial microflora of the leaf. The ratio of streptomycin resistant to susceptible bacterial cells was higher in the treated trees than in the unsprayed check trees after three months. It appears that streptomycin does not have any effect on the presence of resistant fluorescent oxidase positive pseudomonads (groupe IV and V) but it did increase the population level of this bacterium. However no effect of the antibiotic was seen on the development of other streptomycin-resistant microflora which appeared after five days of incubation. Fifty-two bacterial isolates were obtained from the streptomycin-incorporated medium and many of them were found to be resistant to other antibiotics as well. The genes responsible for this antibiotic resistance could not be transfered into E. coli by conjugation.
Manceau, C., Paulin, J.P. and Gardan, L. (1984). EFFECT OF SREPTOMYCIN SPRAYS ON LEAF MICROFLORA ON PEAR TREES. Acta Hortic. 151, 187-194