Nematicidal Potential of <i>Ceriops tagal</i> Extracts and Authentic Compounds against Cyst Nematode <i>Heterodera zeae</i>

<i>Heterodera zeae</i>, a cyst nematode, is a serious pest for economically crucial crops. Six extracts of <i>Ceriops tagal</i> were evaluated against infectious larvae of <i>H. zeae</i> through a glass cavity block assay, causing significant mortality to the larvae. The lower layer of dichloromethane extract (CTDCL) caused 97% mortality (LC₅₀ = 1.64 ppm) at 1% concentration after 72 h. GC-MS and ESI-HRMS analyses of the extracts resulted in the identification of seventy-eight constituents. The activity of the extracts may be attributed to the strong synergistic interactions among the plant constituents. Moreover, nematicidal activity of thirty-four authentic related compounds was also determined; of these, 2,5-dihydroxybenzaldehyde (<b>15</b>), vanillin (<b>17</b>), 2,3-dimethoxybenzaldehyde (<b>18</b>), chrysin (<b>27</b>), and betulinic acid (<b>33</b>) displayed the strongest activity. Their structures have been confirmed through in-depth NMR studies. This research provides templates for the development of eco-friendly bionematicides as a better and safer alternative to synthetic nematicides for the bioprotection of economically vital plants.