Evaluation of a novel endophytic Pseudomonas lactis strain for control of boxwood blight

Abstract

Boxwood blight, caused by Calonectria pseudonaviculata (Cps) (Synonyms: Cylindrocladium buxicola, Cylindrocladium pseudonaviculatum), is a devastating disease which affects boxwood (Buxus) in private and public gardens worldwide. SW, an endophyte identified as a strain of Pseudomonas lactis, was isolated along with seven other bacterial strains from symptom-reversed boxwood leaves infected by Cps. SW had the largest population among the 8 isolates. SW inhibited Cps culture growth similar to three other antagonistic isolates but was the strongest suppressor of Cps conidial germination and germling development. When the cell-free supernatant (CFS) from SW liquid cultures was used to treat boxwood plants 48 h prior to inoculation with Cps, it resulted in a 69.4% disease reduction; suggesting involvement of its metabolites in disease suppression. Boxwood blight control efficacy was further evaluated with resuspended SW cell at 108-9 cfu·ml-1 at different treatment lead times. When SW was applied 2 or 10 days before inoculation with Cps, boxwood blight disease decreased by 72% and 67%, respectively. Further extending the lead time to 20 and 30 days, the efficacy was reduced to 26-27%. However, with its features of moderate control efficacy, high population in plant tissue and safety towards humans, SW shows great potential as a biocontrol agent for boxwood blight.