Bacterial canker of sweet cherry trees, caused by the bacteria Pseudomonas syringae pv. syringae (PSS), is an economically important disease in Michigan and effective disease management is not available. For these reasons, bacteriophages (phages) are being investigated as a potential biological control of bacterial canker. A cocktail of Pseudomonas bacteriophage was tested as a biological control in Michigan sweet cherry orchards during bloom in 2021 and 2022. Populations of antibiotic-marked pathogenic PSS strains were tracked for the duration of the flowering period. Establishment of PSS populations greater than 5 log10 CFU g-1 flowers were detected on all water treated flowers during the experiment. In one field replicate on sweet cherry variety 'Benton', the PSS population on flowers treated with the phage cocktail was lower (P < 0.05) 48 hrs after treatment. Environmental conditions during this field experiment were different compared to the other replicates including higher precipitation, higher relative humidity, and lower Daily Light Integral. These observations could indicate conditions in which phage may be an effective biological control. It also corroborates the need for reducing phage degradation by UV in the field. Kaolin clay was tested as a protectant against UV irradiation in vitro and in vivo. A rate of 4.8 mg ml-1 kaolin clay was shown to effectively protect phage from UV degradation in vitro but was not observed when the phage cocktail was supplemented with kaolin clay in the field. This work gives us a better understanding of the potential of phage as a biological control of bacterial canker under field conditions.
Read
