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Uptake and Persistence of Oxytetracycline in Aster Plants and Vector Leafhoppers in Relation to Inhibition of Clover Phyllody Agent. R. C. Sinha, Chemistry and Biology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Ontario, KlA OC6; E. A. Peterson, Chemistry and Biology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Ontario, KlA OC6. Phytopathology 62:377-383. Accepted for publication 15 July 1971. DOI: 10.1094/Phyto-62-377.

Oxytetracycline-HCl (terramycin) was shown, by microbiologic assay, to be absorbed from solution by roots of aster plants (root treatment) and translocated to stems, petioles, and leaves. Extending the root treatment from 1 to 4 days increased the relative concentration of antibiotic in the extracts of aerial tissues. The concentration gradually declined thereafter, but antibiotic could still be detected 19 days after initiation of treatment, irrespective of the original concentration. Antibiotic was not detected in plants after a single application of terramycin to the leaves (by spraying) or to the soil. Leafhoppers, Macrosteles fascifrons, that were caged on asters whose roots were immersed in terramycin solution (100 ppm), also accumulated active antibiotic in their bodies, the concentration being dependent upon the length of the feeding period. Root treatment (terramycin, 100 ppm) of clover phyllody-affected asters resulted in remission of symptoms in most plants. Fewer leafhoppers were able to acquire and transmit clover phyllody agent (CPA) when fed on antibiotic-treated infected plants than when fed on infected but untreated plants. Healthy aster plants did not become infected when subjected to the root treatment either immediately before, or soon after, inoculation by infective leafhoppers. As the interval between inoculation and antibiotic treatment increased, the number of plants that eventually became infected also increased. After an acquisition access period of 7 days, CPA in leafhoppers was inactivated, as determined subsequently by their ability to transmit, when they were caged on aster plants maintained in terramycin solution (100 ppm). The degree of inactivation was dependent upon the length of time the leafhoppers were allowed to ingest the antibiotic from plants. Healthy leafhoppers that injested the antibiotic lived much longer than did untreated insects. Ultrathin sections of infected plants and vector tissues treated with the antibiotic showed that the mycoplasma bodies (found associated with the disease) were often broken or devoid of their internal structure.