Association of induced disease resistance of rhododendron seedlings with inoculation of Streptomyces sp R-5 and treatment with actinomycin D and amphotericin B to the tissue-culture medium

Seedlings of rhododendron were treated by adding Streptomyces sp. strain R- 5, actinomycin D and/or amphotericin B to the tissue-culture medium. HPLC a nalysis showed that all of the treated seedlings contained these antibiotic s at concentrations higher than the suppressive levels to mycelial growth o f Pestalotiopsis sydowiana, a major pathogen of rhododendron. Occurrence of disease caused by this fungus in the seedlings was suppressed by treatment of the medium surface with strain R-5, but not by treatment with these ant ibiotics, suggesting that growth of strain R-5, an antibiotic producer, cou ld be essential for induction of disease resistance in tissue-cultured seed lings of rhododendron.