Rhabdopeptides from Xenorhabdus budapestensis SN84 and Their Nematicidal Activities against Meloidogyne incognita.

For decades, plant parasitic nematodes have caused serious damage to crop production. Most nematicides are banned because of their negative impacts on the environment and public health. The repeated application of the few commercially available nematicides has caused more incidences of nematicide resistance. To seek novel nematicides, seven linear peptides named rhabdopeptides I-O, 1-7, were isolated from culture broth of Xenorhabdus budapestensis SN84. The structures of the peptides were elucidated on the basis of extensive mass spectrometry (MS), and nuclear magnetic resonance analyses. 3, 4, and 7 were novel compounds. 1, 2, 5, and 6 were isolated and purified for the first time, despite being previously elucidated from an extract mixture based on labeling and MS experiments. All seven compounds were tested for their nematicidal activities against the second-stage juveniles (J2) of Meloidogyne incognita using 24-microwell plates. Rhabdopeptide J, 2, demonstrated strong inhibitory activity with an LC50 value of 27.8 μg/mL. Rhabdopeptide K, 3, and M, 5, showed moderate inhibitory activity with LC50 values of 46.3 and 42.4 μg/mL, respectively.