In vitro and field efficacy of fungicides and postharvest 1-methylcyclopropene against dry lenticel rot (Ramularia mali).

Dry lenticel rot, caused by the ascomycete Ramularia mali, is an emerging postharvest threat to apple production in European alpine regions. Despite its increasing prevalence, established control strategies remain unavailable. This study evaluated the efficacy of 16 fungicides, including succinate dehydrogenase inhibitors (SDHIs; Group 7), demethylation inhibitors (DMIs; Group 3), quinone outside inhibitors (QoIs; Group 11), and multi-site inhibitors, alongside two plant fortifiers. Furthermore, the potential of the ripening inhibitor 1-methylcyclopropene (1-MCP) was tested after harvest. In vitro sensitivity assays showed that most tested active substances had limited inhibitory effects, with the exception of metiram and prothioconazole, which achieved 100% growth inhibition at 100 mg L-1. Two-year field trials largely reflected these findings, although the plant fortifier acidic clay provided a significant reduction in symptom expression, comparable to the levels achieved by prothioconazole. Notably, application of 1-MCP markedly mitigated disease progression, lowering symptom expression by up to 82-89%. The highest level of control was achieved through the combined application of different fungicides in an integrated strategy followed by 1-MCP application in postharvest. These findings suggest that senescence management may contribute to controlling R. mali in commercial apple production. However, the physiological mechanisms underlying the effect of 1-MCP require further investigation.