QoI계 살균제에 대한 사과점무늬낙엽병균 Alternaria alternata f. sp. mali의 저항성 검정

다국어 초록 (Multilingual Abstract)

Alternaria alternata f. sp. mali causes Alternaria leaf spot, a major disease requiring constant management in apple orchards in Korea. However, there are limited studies on fungicide resistance in Alternaria alternata f. sp. mali. To date, there is no study on the resistance to quinone outside inhibitor (QoI) fungicides that have been extensively used in apple orchards. We evaluated 96 Alternaria alternata f. sp. mali isolates, collected from apple orchards in Chungju, Jangsu, Jecheon, and Jinan in 2021, for their sensitivity to the QoI fungicide kresoxim-methyl on the basis of spore germination inhibition. Among the 96 isolates tested, 83 isolates (86.5%) exhibited a high level of resistance to kresoxim-methyl with EC₅₀ values greater than 100 µg/mL. Similarly, all 83 isolates were also resistant to trifloxystrobin because their EC₅₀ values were greater than 100 µg/mL. This suggests cross-resistance between QoI fungicides. Sequence analysis of the cytochrome b gene revealed that all the resistant isolates possessed the G143A mutation (GGT→GCT) at codon 143. On the basis of this mutation, we developed an allele-specific PCR assay using resistance-specific primers and a PCR-restriction fragment length polymorphism (PCR-RFLP) assay using the restriction enzyme Fnu4HI to rapidly detect QoI-resistant isolates. Our results demonstrate that QoI resistance is widely distributed in the Alternaria alternata f. sp. mali populations of apple-growing regions in Korea. To establish effective management strategies for Alternaria leaf spot, our findings suggest that it is critical to continuously monitor fungicide resistance.