The apple is the second most important fruit in Brazil. However, apple cultivars are susceptible to several diseases that can cause losses after harvesting. Bitter rot is caused by the fungus Colletotrichum gloeosporioides and is one of the most damaging summer diseases. The goal of this work was to evaluate the behavior of this fungus in four apple cultivars grown in Brazil (Fuji, Gala, Golden and Green) under two treatments: direct inoculation and isolated fungus. The fungus was isolated by taking fragments from infected fruits, which were stored on Potato Dextrose Agar (PDA) in a laboratory. For the direct treatment, the fungus was removed from infected fruits and directly inoculated into healthy fruits. After inoculation, the fruits were kept at room temperature and the halos of degradation were evaluated every 48 hours. The results demonstrated that direct inoculation was more pathogenic, that the Gala cultivar was the most resistant to the pathogen, and that the Golden cultivar was the most susceptible.