First report of fludioxonil resistance isolate of Colletotrichum fructicola emerging on strawberry in Japan

The species composition of the strawberry anthracnose pathogen population in Saga Prefecture was investigated through phylogenetic analysis of the nucleotide sequences of the intergenic regions of the apn2 and MAT1-2–1 genes. Here, 77 out of the 80 Colletotrichum isolates used were classified as C. fructicola, and the remaining three were classified as C. siamense. The 77 C. fructicola isolates were tested for sensitivity to fludioxonil, which is widely used as the main fungicide in rotational programs in Saga Prefecture. High levels of resistance to fludioxonil were observed in 14 C. fructicola isolates tested for sensitivity to mycelial growth in fludioxonil-containing media. Furthermore, two inoculation assays using strawberry seedlings treated with fludioxonil were performed on five of the 14 isolates that showed high levels of resistance. The effectiveness of fludioxonil was significantly low in these isolates. To our knowledge, this is the first study to report fludioxonil resistance in a C. fructicola population.