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

Abstract

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 MAT1-2-1genes. Here, 77 out of the 80 Colletotricum isolates used were classi ed as C. fructicola, and the remaining three were classi ed as C. siamense. The 77 C. fructicola isolates were tested for sensitivityto udioxonil, which is widely used as the main fungicide in rotational programs in Saga Prefecture. High levels of resistance to udioxonil were observed in 14 C. fructicola isolates tested for sensitivity to mycelial growth in udioxonil-containing media. Furthermore, two inoculation assays using strawberry seedlings treated with udioxonil were performed on ve of the 14 isolates that showed high levels of resistance. The effectiveness of udioxonil was signi cantly low in these isolates. To our knowledge, this is the rst study to report udioxonil resistance in a C. fructicola population.