Standard 14‐cm plastic‐petri dishes were used as root substrate chambers allowing controlled inoculation, regular inspection under the dissecting microscope, and manipulation of root infections with pathogens and mycorrhizal fungi under nonsterile conditions. Roots of young pine seedlings were placed on the root substrate and, especially those growing on the substrate surface under the lid, were very easy to manipulate. Mycorrhizal species and inoculation methods were compared and the infection process followed continuously under various conditions. The air pockets formed between the lid and the substrate favoured mycorrhiza formation. Brief, periodic flooding prevented formation of mycorrhizas in two mycorrhizal species having hydrophobic hyphae but did not prevent it in less hydrophobic species. IAA treatment of roots led to heavy production of mycorrhizas. Fruiting body formation inLacearia laccatawas induced and followed in the dish cultures. Pure mycorrhizal stock cultures were able to be revitalized in the dish cultures and reisolated in pure culture. The infection strategy of a weak root pathogen,Cylindrocarpon destructans, was studied with the same technique, which was also used for investigating treatments predisposing seedlings to pathogen infection.