Multi-site evaluation of Chilean native rhizobacteria for the sustainable management of the walnut root-lesion nematode Pratylenchus vulnus (Tylenchida: Pratylenchidae).

Pratylenchus vulnus is the most damaging nematode affecting walnut (Juglans regia L.) worldwide, but evidence on the performance of biological control agents under commercial orchard conditions remains limited. We evaluated two native Chilean rhizobacteria (Bacillus mycoides 25 and Oerskovia sp. UCH-1055), previously shown to achieve >98% in vitro mortality and 76% biocontrol efficacy under greenhouse conditions, using application strategies combining inoculum concentrations of 106-108 CFU mL-1, with or without reinoculation after 30 or 60 days, alongside untreated and chemical controls. Treatments were first evaluated under greenhouse conditions and subsequently validated in multi-site field trials across three commercial walnut orchards representing geographically distinct regions. Greenhouse experiments showed no statistically significant differences among treatments, despite numerical trends favoring bacterial applications. Field trials revealed strong site-dependent efficacy with significant suppression of P. vulnus populations in two of three orchards (Buin and Requínoa), corresponding to Reproductive Index reductions of 70-83% relative to untreated controls. Spatial patterns were consistent with reductions in high-density P. vulnus areas at these responsive sites. By contrast, rhizobacterial treatments did not produce major consistent changes in the abundance of non-target free-living nematodes. These results provide multi-site field validation of native rhizobacteria against P. vulnus, highlighting the biocontrol potential of Oerskovia sp. UCH-1055 under responsive field conditions, and the need to evaluate rhizobacterial performance across multiple commercial sites before broader implementation.