Chemical sensitivity phenome of an <i>Armillaria mellea</i> isolate determined using phenotype microarrays and potential use of caffeine-rich wastes for disease control

Armillaria fungi are frequently documented as economically and ecologically significant plant pathogens, recognised as the causal agents of Armillaria root rot disease. Armillaria mellea is one of the most aggressive pathogens in the Armillaria genus. None of the chemicals tested against Armillaria have been effective in fully eradicating an established A. mellea mycelium from an infection site and/or preventing plant mortality, which makes studies about the chemical sensitivity of A. mellea essential. In this work, the inhibitory effects of 120 different chemical agents on the growth rate of A. mellea were examined using the Biolog Phenotype MicroArray system of chemical sensitivity panels. Among the tested substances, aromatic and membrane function compounds showed the highest inhibitory activity against A. mellea. Interestingly, our results demonstrated promising potential for application of caffeine as an A. mellea-oriented fungicide. Further studies were conducted to explore the antifungal activity of a low-cost and locally available caffeine-rich waste, i.e. spent coffee grounds (SCG) against A. mellea. It is noteworthy that the hyphal growth of A. mellea was significantly inhibited when cultivated on malt extract agar supplemented with SCG. Current findings uncovered, for the first time, the potential use of caffeine-rich wastes for designing management strategies to practically control the spread of A. mellea.