PPM™ (Plant Preservative Mixture) is a heat stable preservative/biocide that, based on the dose, effectively prevents or reduces microbial contamination in plant tissue culture. At optimum doses, PPM™, does not impair in vitro seed germination, callus proliferation or callus regeneration. Despite the most stringent use of sterile techniques and aseotic conditions, the contamination of plant cell and plant tissue cultures remain a persistent problem.