Allicin suppresses preharvest soft rot associated with a Diaporthe sp. and enhances defense responses in 'Ancui' hardy kiwi.

Preharvest soft rot poses a threat to the commercial development of 'Ancui' hardy kiwi (Actinidia arguta), a newly developed cultivar with increasing cultivation potential in the cold northern regions of China. However, the fungus associated with this disease and environmentally friendly strategies for its management remain insufficiently understood. In this study, a fungal isolate was recovered from symptomatic fruits and characterized through morphological observation, internal transcribed spacer (ITS) sequence analysis, phylogenetic analysis, and pathogenicity tests. Based on the combined evidence, the fungus was assigned to the genus Diaporthe and conservatively designated as Diaporthe sp. isolate B4. A commercial 6% allicin emulsifiable concentrate exhibited concentration-dependent antifungal activity against the isolate in vitro, with an EC50 of 326.90 mg/L on a formulation-concentration basis. In a field trial, two applications of allicin at 800-1,000 mg/L provided the highest disease control efficacy, reaching approximately 82%. Allicin treatment also reduced superoxide anion production and malondialdehyde accumulation while increasing the activities of superoxide dismutase, peroxidase, catalase, and phenylalanine ammonia-lyase in fruit tissues. These findings suggest that the suppression of preharvest soft rot by allicin may involve both direct antifungal activity and enhanced defense-related responses in hardy kiwi fruit. Allicin therefore represents a promising botanical option for the sustainable management of preharvest soft rot in 'Ancui' hardy kiwi.