Abstract: A microcidal composition consisting of a water-soluble polymer and the active principle 1-(5-bromophur-2-yl)-2-bromo-2-nitroethene is provided to be used as chemical sterilizer of culture media for the control of bacterial and fungal contaminants. This technical solution, even can be used for the sterilization of solid and liquid culture media, is particularly useful in the production of “in vitro” cultivated plants, and surprisingly was found that its utilization can substitute completely the previous process of sterilization that this media require and even more, the addition of the necessary hormones in the rootage process of “in vitro” plants of crops.