Advancing the Development of <i>Pseudomonas protegens</i> <scp>PBL3</scp> Secretome as a Biopesticide to Control Bacterial Panicle Blight in Rice

ABSTRACT Bacterial panicle blight (BPB), caused by Burkholderia glumae , is an emerging disease in rice that threatens global food security in the absence of effective strategies to control it. The environmental bacterium Pseudomonas protegens PBL3 produces and secretes a collection of molecules (secretome) with demonstrated antimicrobial activity in vitro against B. glumae , suggesting that this P. protegens PBL3 secretome can be exploited as a source of an environmentally friendly management strategy against BPB. However, the effectiveness of the P. protegens PBL3 secretome under greenhouse and field conditions has not been investigated, as they require large volumes of the active product. In this work, we optimised fermentation conditions to successfully scale up the production of P. protegens PBL3 secretome from 20 mL to 6 L while retaining its antimicrobial activity. Lyophilisation of the P. protegens PBL3 secretome obtained at large scale facilitated testing of several concentrations to identify the minimal inhibitory concentration in vitro and in planta. We further demonstrated that spraying the P. protegens PBL3 secretome at 0.1 g/mL in rice panicles prior to B. glumae inoculation significantly reduced B. glumae populations and BPB symptoms. These results will pave the way towards advancing the use of the P. protegens PBL3 secretome to alleviate the impact of BPB.