Control of coffee canker associated with Pseudomonas coronafaciens pv. garcae using a cocktail integrating two virulent polyvalent bacteriophages encapsulated in nanoparticles: in planta studies

Aims: In this study we report the use of two novel lytic polyvalent phages as a cocktail in in planta assays and its efficacy in the control of bacterial halo blight (BHB) caused by Pseudomonas coronafaciens pv. garcae (Pcg) in coffee plants.

Methods and results: Phages were isolated from samples of coffee plant leaves collected at two different locations in Brazil. Both phages belong to the class Caudoviricetes and present myovirus-like morphotypes, and both exhibited specificity to their host, Pcg strain IBSBF-158. The two phages were encapsulated in chitosan-coated Ca-alginate nanoparticles, which demonstrated promising performance, promoting reductions in disease severity ranging from 66.83% to 83.37%, depending on the timing of application relative to infection. Both phages were somewhat susceptible to the effects of abiotic factors when in free form, with solar radiation seriously negatively impacting their lytic activity. However, nanoencapsulation of both phages as a lytic cocktail within chitosan-coated Ca-alginate nanoparticles proved successful in fully stabilizing both phages from the deleterious action of UV radiation.

Conclusions: Application of such lytic nanoparticles in pre- and post-inoculated coffee seedlings in in planta greenhouse assays proved successful in controlling the phytopathogen responsible for BHB of coffee, Pcg, with a significant decrease in the progression of the disease. The results suggest that lytic nanoparticles may become an effective and sustainable strategy for coffee BHB control, as an alternative to conventional approaches relying on chemical (copper hydroxide or oxychloride, or kasugamycin hydrochloride) or biological agents, but more studies are needed in the field to confirm this. The phage protection system developed represents a potential alternative treatment for bacterial plant diseases with minimum damage to the environment.