ABSTRACT.- Bitter rot (BR), caused by Colletotrichum spp., is one of the most prevalent fungal diseases of apple worldwide. Some Colletotrichum spp. also causes Glomerella leaf spot (GLS), a disease restricted to a few regions worldwide. Recently, we reported the presence of C. siamense causing BR on low-chill apple cultivars in central Argentina. In further studies we detected the presence of apple leaf spot also associated to Colletotrichum spp. Thus, this study was focused to determine and characterize the Colletotrichum species involved in fruit rot and apple leaf spot diseases in Santa Fe, Argentina. A total of thirty-one isolates were obtained from symptomatic fruits and leaves. Morphological characteristics in combination with multilocus phylogenetic analysis revealed that Colletotrichum siamense is the single species associated with fruit rot and leaf spots on low-chill apples in Santa Fe, Argentina. Although in this study we obtained and characterized isolates of C. siamense from leaf spot, we found remarkable differences with typical GLS indicating that this disease is not present in Argentina until now. These findings will be useful to undertake studies of fungicide sensitivity and to understand the epidemiology of the disease in the region based on identified species. © 2022 Informa UK Limited, trading as Taylor & Francis Group