CHARACTERIZATION OF BACTERIA CONTAMINATING TISSUE-CULTURES OF APPLE ROOTSTOCK YP

Meristem-tip cultures of apple rootstock 'YP' were started at different times of the year over a period of 2 years and the contamination of the cultures was monitored during five subcultures. Bacterial contaminants were isolated to pure cultures, identified by the API test system and appropriate additional tests, and the sensitivity of the most common isolates to different antibiotics was determined. Of the 216 strains isolated from the initiation cultures, 78% were pseudomonads, coryneforms or enterobacteria. Only three bacterial contaminants were found at the multiplication stage. A greater part of the contaminants were likely to originate from the stock plant. Rifampicin (at 50-200 mg l(-1)) and cefotaxime (at 250-1500 mg l(-1)) were found to be bactericidal against many isolates, but differences between species and strains were found.