Plant Preservative Mixture™(PPM), a relatively new, broad-spectrum preserva-tive and biocide for use in plant tissue culture, was evaluated as an alternative to the use of conventional antibiotics and fungicides in plant tissue culture. Concentrations of 0.5 to 4.0 mL· L–1 were tested with leaf explants of chrysanthemum (Dendranthema× grandiflora Kitam), European birch (Betula pendula Roth), and rhododendron (Rhododendron catawbiense Michx.). PPM had little effect on the percentage of explants forming shoots and the number of shoots formed per explant in birch and rhododendron, but dramatically reduced both responses in chrysanthemum. Therefore, the effects of PPM must be evaluated for each species of interest prior to use.

Microbial contamination is the single most important reason for explant loss in plant tissue culture (Boxus and Terzi, 1987; Cassells, 1991). Plant Preservative Mixture™(PPM)(Plant Cell Technology, Washington, DC) is a relatively new, broad-spectrum preservative and biocide for use in plant tissue culture. The active ingredients are 5-chloro-2-methyl-3 (2H)-isothiazolone and 2-methyl-3 (2H)-isothiazolone. PPM is effective against both bacteria and fungi, is heat stable, and, unlike conventional antibiotics, can be autoclaved in the media. These characteristics of PPM make it an attractive alternative to using conventional antibiotics and fungicides in plant tissue culture.