Phytotoxic Metabolites Produced by <i>Corynespora cassiicola</i> , the Causative Agent of Rubber Tree <i>Corynespora</i> Leaf Fall Disease

<i>Corynespora</i> leaf fall disease (CLFD), caused by <i>Corynespora cassiicola</i>, results in significant leaf shedding, reduced photosynthetic efficiency, and decreased latex production. This study reports the isolation and characterization of 12 secondary metabolites from the strain CC01, obtained from <i>Hevea brasiliensis</i> in China. Among these metabolites, four are new compounds (<b>1</b>-<b>4</b>), while eight are previously identified (<b>5-12</b>), all classified within the polyketone group. Their structures were determined using nuclear magnetic resonance and mass spectrometry analyses. Toxicity evaluations revealed that compounds <b>4</b>, <b>5</b>, <b>6</b>, <b>8</b>, and <b>9</b> exhibited notable phytotoxic effects on the leaves and anther calli of <i>H. brasiliensis</i>, with compound <b>4</b> identified as the primary phytotoxin. These phytotoxic compounds induce leaf necrosis and callus damage by compromising cell membrane integrity and initiating programmed cell death. This finding enhances the understanding of the chemical mechanisms underlying its pathogenicity and provides potential molecular targets for the development of novel disease control strategies.