Monitoring Lysobacter capsici AZ78 using strain specific qPCR reveals the importance of the formulation for its survival in vineyards

Survival in the phyllosphere is a critical feature for biofungicides based on non-spore forming bacteria. Moreover, knowledge of their ecological fitness when applied to plants is important to design effective formulations and application techniques. With this scope, the aim of this work was to develop a specific method to monitor the fate of Lysobacter capsici AZ78, a biocontrol agent of Plasmopara viticola, in the environment and to evaluate the persistence of formulated cells of L. capsici AZ78 in vineyards, compared to unformulated ones. A strain specific primer pair was designed based on REP-PCR fingerprinting and used in qPCR experiments to track the evolution of the L. capsici AZ78 population in vineyards. The population reached between 5 and 6 log10 cells gram of leaf-1 after application and decreased by more than two orders of magnitude in one week, becoming undetectable after two months. The decrease in the number of cells correlated with unfavourable temperature and relative humidity, solar radiation and rainfall. The use of formulation additives significantly improved the persistence of L. capsici AZ78 on the leaves, indicating that the formulation is a crucial step for a non-spore forming bacterium such as L. capsici AZ78, when used as a biocontrol agent for foliar application.