Reclassification of the Main Causal Agent of Glomerella Leaf Spot on Apple intoColletotrichum chrysophilumin Southern Brazil and Uruguay

Abstract

Glomerella leaf spot (GLS) is one of the most important diseases of apple, affecting a wide range of economically important cultivars, particularly Golden Delicious and its descendants. Caused mainly by species of the Colletotrichum gloeosporioides species complex (CGSC), C. fructicola has been described as the most prevalent and aggressive species associated with GLS and apple bitter rot (ABR) in Brazil and Uruguay. Recently, new CGSC species, closely related to C. fructicola, have been identified causing ABR. To verify the accuracy of species identification within the CGSC, we aimed to reevaluate the identity of representative GLS-causing isolates from Brazilian and Uruguayan populations, previously identified as C. fructicola. Multilocus phylogenetic analysis based on APN2, ApMAT, CAL, GAPDH, GS, ITS, and TUB2 allocated these isolates in a monophyletic clade with C. chrysophilum. This species was first described as the causal agent of anthracnose in banana fruits in Brazil, and recent reports indicate its association with ABR in the United States. This is the first report of C. chrysophilum causing GLS disease on apple worldwide.