Antagonistic activity of microorganism in media cutures is not only dependent to type but related to many factors, as thickness of soild media, acidity, duration of autoclave sterilization, how freshly is medium and .... Therefor in Petri dishes assay is only primary check and you should go from in situ to in vivo to be sure about effectiveness.

Dear Meysam, thank you for your valuable answer.

A lot of soil micro-organisms are able to generate secondary metabolites with antimicrobial activity. It's well known by all microbiologists that it often happens under certain growth phases for example during stationary phase, probably different culture media generates different growth rates or different metabolic scenarios.

Dear Francesc, Thank you.

I agree with Mr. Codony...