Nematicidal effects of Photorhabdus- and Xenorhabdus-derived compounds against plant-parasitic nematodes: a systematic review and meta-analysis

Plant-parasitic nematodes (PPNs) are major agricultural pests that cause substantial yield losses worldwide. However, developing sustainable alternatives to synthetic nematicides remains a critical challenge. Bacterial symbionts of entomopathogenic nematodes, particularly species of Photorhabdus and Xenorhabdus, have emerged as promising sources of bioactive compounds with nematicidal activity. Despite increasing experimental evidence, the overall effectiveness of Photorhabdus spp. and Xenorhabdus spp. and their nematicidal compounds remains to be assessed. Here, we conducted a systematic review and a meta-analysis to quantify the nematicidal effects of Photorhabdus- and Xenorhabdus-derived compounds against PPNs and characterize current experimental trends. Studies were identified from two databases (Web of Science Core Collection and Scopus) and screened according to PRISMA guidelines. A total of 27 studies were included in the qualitative analysis, and 12 of them provided appropriate data for quantitative analysis. The available literature is strongly biased toward in vitro assays targeting Meloidogyne spp., particularly M. incognita, and predominantly evaluates cell-free supernatants as bioactive preparations. Bacterial-derived compounds showed a positive effect on PPN suppression. The effect size was statistically significant under in vitro conditions, whereas in vivo studies showed lower effects with confidence intervals overlapping zero, indicating a non-significant trend toward nematode suppression. Our findings provide quantitative evidence that Photorhabdus- and Xenorhabdus-derived compounds have consistent nematicidal potential against PPNs. Future research should focus on expanding taxonomic coverage and improving experimental reproducibility to better assess their effectiveness under field conditions.