Effect of Antibiotics on the Symptoms of Stunting Disease of Magnolia liliiflora Plants

Treatment of diseased magnolia plants with Oxytetracycline, Baytril or Tylan did not reduce the number of symptomatic plants, but promoted shoot growth, development of symptomless leaves and flower buds. The most efficient were 500 ppm Baytril, 200 ppm Tylan and 500 or 1000 ppm Oxytetracycline. Lower concentrations of Baytril and Oxytetracycline were less effective and higher concentrations of Tylan decreased the growth of magnolia shoots. All the tested antibiotic treated and untreated magnolias were shown by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) to contain the AY (16SrI) phytoplasma and two also to contain a phytoplasma related to apple proliferation phytoplasma group (16SrX). The results indicate that Magnolia is a natural host of phytoplasmas belonging to the aster yellows and apple proliferation phytoplasma groups, and support the suggestion that phytoplasmas are the cause of magnolia stunting disease.