From the mass production and formulation to the fate in the environment of Lysobacter capsici AZ78, a biological control agent of Plasmopara viticola

Abstract: The antagonistic bacterial strain Lysobacter capsici AZ78 was recently selected for its relevant efficacy in controlling Plasmopara viticola under greenhouse conditions. Since little is known about how Lysobacter spp. may respond to desiccation, rain wash-off, and UV light, the aim of this work was to design formulations, which can effectively protect L. capsici AZ78 cells by these environmental stressors when applied in the vineyards. Firstly, fermentation conditions were optimized to achieve a harvest of 1010 L. capsici AZ78 cells/ml after 24 h and the shelf-life at 4 °C indicated only a decrease of an order of magnitude after one year. Polyethyleneglycol, corn steep liquor and lignosulfonate were subsequently selected for the protection of L. capsici cells against desiccation, wash-off and UV light and were combined to implement a liquid formulation. The efficacy of L. capsici AZ78 formulated cells against P. viticola on grapevine under field conditions was higher than the unformulated ones. Finally, the fate in the environment of L. capsici AZ78 cells was assessed through a strain specific qPCR protocol. Results showed that the negative effect played by solar radiation, rainfall, unfavourable temperature and relative humidity on the unformulated AZ78 cells was mitigated by the formulation. The procedure followed in this work allowed to produce a first prototype formulation of L. capsici AZ78, that made this biocontrol agent more efficient in persisting on grapevine leaves and, consequently, controlling P. viticola under field conditions.