Rhizospheric Bacillus subtilis and Bacillus stercoris suppress Heterodera schachtii and promote Arabidopsis thaliana growth

Cyst nematodes are major pathogens of economically important crops. Chemical control options often raise environmental concerns and underscore the need for sustainable alternatives. Plant growth-promoting rhizobacteria offer a promising strategy because they can simultaneously enhance plant growth and suppress nematodes. This study investigated the biocontrol potential of seven rhizobacterial isolates (SC11, SW33, SW44, SW53, SW69, SW73, and SW83) against Heterodera schachtii . In vitro both living bacterial cells (LBC) and cell-free supernatants (CFS) significantly increased mortality of infective juveniles (J2) with LBC of SW44 and SW73, and CFS of SW33 causing the highest J2 mortality, up to ∼48% and ∼64%, respectively. Nematode infection assays with Arabidopsis thaliana confirmed that all isolates reduced H. schachtii parasitism. SW83 in particular decreased the number of developed females by ∼69%. The isolates reduced J2 root invasion by up to 46% (SC11), the development into adults (by ∼26% SW33, ∼34% SW73, ∼36% SW83), and female size (by 12% SC11 to 18% SW44 and SW83). Additionally, SW33, SW53, SW69, and SW73 significantly improved plant growth variables. 16S rRNA sequencing assigned SC11, SW33, and SW53 to Bacillus subtilis and SW44, SW69, SW73, and SW83 to Bacillus stercoris . All isolates produced biofilm and siderophores, while SW44, SW73, and SW83 secreted chitinase, SW33 produced hydrogen cyanide, and SW33 and SW44 solubilized phosphate. This study demonstrates that Bacillus isolates can effectively suppress H. schachtii , provides the first evidence for antagonistic activity of B. stercoris against a plant-parasitic nematode, and highlights the isolates’ potential as components of integrated nematode management.