Abstract: The present invention encompasses compositions and methods to reduce or prevent microbial growth in plant tissue culture media, comprising adding a chemical agent comprising methylchloroisothiazolinone, methylisothiazolinone, magnesium chloride and magnesium nitrate to a plant culture medium at a concentration that reduces or prevents microbial contamination of the plant tissue culture medium and that allows substantially normal germination of seeds or substantially normal growth or development of plants, plant organs, plant tissues or plant cells. The chemical agent may further comprise potassium sorbate or sodium benzoate, or both. The present invention further provides a kit for germinating plant seeds or culturing plants, plant organs, plant tissues or plant cells on a plant tissue culture medium comprising the chemical agent.