The effects of 0, 1.5 and 3 KGy gamma-irradiation on Brown Rot disease affecting Golden Delicious apples are investigated. The apples were artificially inoculated with Monilinia fructigena fungus before and after irradiation. Results show clearly that radiation induces a delay in fungus development, even when it is not directly affected. The effect of radiation on the apples' substrate seems to be considerable, being the main factor affecting fungal growth. Radiation doses of 1.5 and 3 KGy do not seem to produce strong differences in the fungal growth. Irradiation, however, is very effective, producing important changes of practical interest for apples infected before or after irradiation.