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Effect of Tetracycline Antibiotics on Symptom Development of Stubborn Disease and Infectious Variegation of Citrus Seedlings. E. C. K. Igwegbe, Postgraduate Research Plant Pathologist, Department of Plant Pathology, University of California, Riverside 92502; E. C. Calavan, Professor of Plant Pathology, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 63:1044-1048. Accepted for publication 10 February 1973. DOI: 10.1094/Phyto-63-1044.

Uptake, translocation, and effect of tetracycline compounds on development of symptoms of stubborn and on those of citrus infectious variegation were investigated. We demonstrated, using Bacillus cereus as a test organism, that shoot extract of healthy sweet orange seedlings grown in tetracycline-HCl (achromycin) solution contained higher antibacterial activity than did shoot extract of similar seedlings grown in chlortetracycline-HCl (aureomycin) solution. Thin-layer chromatography of shoot extract of treated plants revealed achromycin but not aureomycin, suggesting that the latter is not readily translocated upwards or is rapidly inactivated in plant shoots or their extracts. Tetracycline compounds applied to roots of citrus seedlings inoculated with citrus infectious variegation virus were ineffective in suppressing disease symptoms. Stubborn symptom development in infected seedlings was completely suppressed by tetracycline compounds applied to the roots as a dip or in hydroponic culture. Tetracycline compounds as quartz sand drenches were ineffective in suppressing stubborn symptom development. Achromycin, which appeared more stable than aureomycin, was more efficacious in suppressing stubborn symptom development. These results and the finding of mycoplasmalike bodies in the phloem of stubborn plants suggest that the stubborn pathogen is a mycoplasmalike organism and not a virus.

Additional keywords: chromatography, citrus infectious variegation virus, mycoplasmalike organism, hydroponic culture, uptake, translocation.