The soil bacterium Lysobacter capsici attaches to the nematode surface, and triggers induced systemic resistance in barley, impairing the invasion of root‐lesion nematodes

Root-lesion nematodes pose a global threat to crop yield and stability, with their broad host range presenting a formidable challenge for effective management. In this study, we investigated the role of the nematode-attached bacterium Lysobacter capsici in mitigating the invasion of Pratylenchus penetrans into spring barley roots. Using a split-root system, we demonstrated that the cuticle-attached bacterium significantly reduced nematode invasion by 75–77% as compared to the nematodes without L. capsici. This reduction was predominantly due to the induction of systemic defense in the plants, and partially due to the bacterium's local antagonism in contact with the nematode. Compared to the nematodes without L. capsici, the reduced root invasion of P. penetrans with attached bacteria differed over time and was particularly observed at 48- and 72 h post-inoculation. Notably, the reduction in nematode invasion was more pronounced when L. capsici cells were attached to the nematode cuticle than when the bacteria were applied systemically and were not directly interacting with the nematodes. In addition, transcriptional analyses revealed a higher expression of the barley pathogenesis-related gene PR1 in response to the nematodes with attached bacteria compared to the surface-sterilized nematodes or L. capsici cells. This suggests that nematodes carry bacteria inside the roots that activate plant defense. Our study showed the potential of L. capsici to effectively manage nematode populations and improve plant health by inducing the plant immune system upon nematode invasion.