IDENTIFICATION AND ELIMINATION OF BACTERIAL CONTAMINANTS FROM Pelargonium TISSUE CULTURES

In our laboratory, bacterial contamination was detected in cultures of Pelargonium x hederaefolium ‘Bonete’ that had been subcultured continuously for several years. Two contaminating bacteria were isolated and identified by partial sequence analysis of 16S rRNA gene as Paenibacillus glycanilyticus and Lactobacillus paracasei. Antibiotic sensitivity testing was performed on the bacterial isolates and four antibiotics were identified as being potentially useful in eliminating these contaminating bacteria: carbenicillin, cefotaxime, neomycin and streptomycin. Neomycin and streptomycin were found to be phytotoxic to Pelargonium shoots. Shoots were grown on multiplication medium containing 0.5 mg l m-topolin supplemented with either 500 mg -1 carbenicillin or 250 mg l cefotaxime and transferred to fresh medium every three weeks. After growing in the presence of carbenicillin for three weeks, bacterial growth was inhibited, but not completely eliminated. Intensive formation of high-quality shoots also took place. After nine weeks of growth on medium supplemented with carbenicillin, 40% of the shoots were free of both contaminating bacteria. After three weeks of growth on medium supplemented with cefotaxime, 37% of the shoots were free of both contaminating bacteria. However, shoots grown in the presence of cefotaxime tended to be shorter and have yellow leaves more so than shoots grown in the presence of carbenicillin. Prolonged exposure to cefotaxime adversely affected shoot formation and eventually resulted in plant death.