In vitro evaluation of the efficacy of 8-hydroxyquinoline derivatives for the control of Phaeomoniella chlamydospora, the causative agent of Petri disease in grapevines.

Aim: This study evaluates the in vitro efficacy of 8-hydroxyquinoline (8HQ) derivatives in controlling the phytopathogenic fungus Phaeomoniella chlamydospora.

Methods And Results: The in vitro tests assessed the susceptibility to the minimum inhibitory concentration (MIC), checkerboard assay, mycelial growth (MG) inhibition, and EC50 determination. Among the seven agricultural fungicides tested, tebuconazole (TEB) displayed the lowest MIC, 1.01 µg mL-1, followed by captan (CAP), thiophanate methyl (TM), and mancozeb with MICs of 4.06, 5.46, and 10.62 µg mL-1, respectively. The 8HQ derivatives used in this study were clioquinol and PH 151 (PH) with MICs of 1.09 and 2.02 µg mL-1, respectively. PH associated with TEB and CAP showed synergism and inhibited 95.8% of MG at the highest dose. TEB inhibited 100% of MG at the three highest doses, while associated with PH exhibited the lowest EC50 (0.863 + 0.0381 µg mL-1).

Conclusions: We concluded that the 8HQ derivatives tested controlled effectively the P. chlamydospora in vitro. PH associated with CAP and TEB exhibited a synergistic effect. The association between PH and TM was considered indifferent.

Impact Statement: This study expands the list of active ingredients tested against P. chlamydospora, with the PH 151 and clioquinol derivatives being tested for the first time. The in vitro efficacy and synergistic action with other fungicides suggest a potential use as a grapevine wound protectant. This association makes it possible to reduce doses and increase the potency of both drugs, reducing the risk of resistance development and harm to humans and the environment.