Inhibitory Effects of 3-Octanone and 1-Octen-3-ol on Juvenile Survival, Egg Development, and Egg-Mass Hatching in Meloidogyne Species

Root-knot nematodes (RKNs) of the genus Meloidogyne are major plant pests causing severe crop losses. Microbial volatile organic compounds (VOCs) have emerged as promising biopesticides. In this study, we evaluated the effects of two fungal VOCs, 1-octen-3-ol and 3-octanone, on nematode survival in five Meloidogyne species (M. incognita, M. javanica, M. hapla, M. arenaria, and M. luci) in plate assays. Results showed near-complete (95–100%) J2 mortality at 500–1000 ppm within 24 h. At lower concentrations, mobility declined, and species-dependent differences were observed: 1-octen-3-ol was more effective against M. arenaria. Meanwhile, 3-octanone showed stronger effects only on M. hapla and moderate effects on M. incognita and M. javanica. Further experiments using solely M. javanica showed that egg differentiation was significantly inhibited at 7, 14, and 21 days, with up to an 80% reduction at 1000 ppm, and the effects persisted at 125 ppm. Egg hatching from egg masses was reduced by up to 95% in a concentration-dependent manner, irrespective of compound type. Soil-like microcosm assays resulted in substantial reductions in recovered juveniles, with over 90% reduction at 125 ppm after 24 h, suggesting sustained effects under the tested conditions. In more complex plant–soil greenhouse conditions, effects were reduced, although decreasing trends in nematode infection were observed. Overall, these results indicate that fungal VOCs exhibit strong effects on different nematode life stages under controlled conditions, highlighting 1-octen-3-ol and 3-octanone as promising candidates for further evaluation in nematode management strategies.