The persistence of accidentally introduced bacterial contaminants in Delphinium tissue cultures can be prevented by acidification of the tissue culture medium. Using this preservation method the contamination rate of Delphinium cultures could be reduced by more than 50%.

Leifert, C., Waites, W.M., Nicholas, J.R. & Keetley, J.W. 1990. Yeast contaminants of micropropagated plant cultures. Journal of Applied Bacteriology69, 471–476. Of 36 yeast strains isolated from contaminated plant cultures 78% were Candida, 20%Rhodotorula and 2% were Cryptococcus species. Strains of Candida guilliermon‐dii represented 45% of all yeasts isolated. Yeasts grew rapidly on plant growth media with a pH of between 2.5 and 6.0 and decreased the medium pH to values of between 2.0 and 3.0. Candida yeasts growing on plant medium for 28 d metabolized about 75% of the sucrose and produced fermentation products such as ethanol and acetic acid. In contrast, Rhodotorula did not produce ethanol or acetic acid and only metabolized about 20% of the sucrose. Possible sources of contamination are discussed.