In Brazil, Colletotrichum gloeosporioides and C. acutatum are responsible for the occurrence of Gala leaf spot or Glomerella Leaf Spot (GLS) on apple. Breeding programs aiming to develop genetic resistance to disease need a complete understanding of the characteristics of involved species. A study of the sensibility of the isolates to benomyl is a way to separate those species. A sensitivity test of 39 isolates of C. acutatum and C. gloeosporioides involved with GLS, evaluated by growth rate and reduction rate of mycelium, revealed a group of C. gloeosporioides isolates that are resistant to the fungicide. This group showed resistance to concentrations of 5 and 100 µg.mL-1 with reduction rate varying between 0% and 8%, and between 15 and 30%, respectively. While the standard C. gloeosporioides isolate (CG197) showed a reduction rate of 100% at both tested concentrations, all isolates of C. acutatum were resistant to the fungicide. Due to the resistance of some isolates of C. gloeosporioides, the separation of Colletotrichum species on apple should not be based only on resistance or susceptibility to benomyl.
Malus spp; fungicide resistance; in vitro growth
