Antifungal Potential of Piper-Derived Essential Oils and Key Constituents on Moniliophthora roreri, the Causal Agent of Moniliasis in Cacao (Theobroma cacao L.)

Moniliophthora roreri, the causal agent of moniliasis, severely affects cacao production in Latin America, and sustainable control alternatives remain limited. This study aimed to evaluate the antifungal potential of essential oils (EOs) from Piper species and selected volatile compounds against M. roreri. A total of 34 EOs obtained by steam distillation were assessed for mycelial growth inhibition under fumigation conditions. The most active EOs (≥60% inhibition) were chemically characterized by GC-MS, and their median inhibitory concentrations (IC50) were determined. Additionally, 40 structurally diverse volatile compounds were selected and evaluated for their antifungal activity to identify the main contributors and explore structure–activity relationships. Most of the active EOs exhibited a high proportion of phenylpropanoids and oxygenated monoterpenoids, with IC50 values ranging from 0.58 to 184.27 µL·L−1; the most active were those from P. holtonii and P. aduncum. Among the 28 most active compounds, IC50 values ranged from 0.48 to 109.81 µL·L−1; the most potent were myristicin and dillapiole. The most potent molecules were phenylpropanoids bearing methoxy and methylenedioxy groups, followed by oxygenated monoterpenoids and long-chain ketones and alcohols. This is the first report of antifungal activity against M. roreri for most of the evaluated EOs and all tested compounds, highlighting the potential of the Piper genus as a source of natural alternatives for sustainable disease management in cacao cultivation.