Evaluation of Fungicide Resistance of the Brown Shot-hole Pathogens of Cherry Trees in Korea

Cherry trees (Prunus serrulata var. spontanea, Prunus × yedoensis), a widely cultivated ornamental street trees grown in Korea, are vulnerable to variety of diseases particularly the prevailing brown shot-hole disease, thus needs effective maintenance strategies for optimum plant growth and observation. The major fungal genera causing cherry brown shot-hole disease in Korea were identified as Alternaria, Diaporthe, Epicoccum, and Botryosphaeria, and their resistance to tebuconazole and difenoconazole was investigated. Both fungicides are classified as demethylation inhibitors and the emergence of resistant strains has been reported worldwide. In this study, we found significant differences in fungicide resistance depending on the type of pathogen and regional differences and performed base sequence analysis of the CYP51 gene on some Alternaria isolates with fungicide resistance to confirm the occurrence of point mutations and amino acid substitutions. However, point mutations were not detected in some resistant Alternaria isolates, suggesting that the resistance of some isolates is possibly unrelated to the alterations in the target site or may be due to genetic variations in unidentified genomic sequence CYP51 gene. These results will contribute to understanding the mechanism of antifungal resistance development in fungal plant pathogens and are expected to contribute to the control of brown shot hole disease in cherry trees.