Biocontrol potential of three bacteriophage strains in control of fire blight

Control of fire blight caused by Erwinia amylovora (Ea), is one of the major challenges in pome fruit production, especially under favorable weather conditions for disease development. Due to lack of effective bactericides and limited effect of preventive measures, we studied efficacy of three strains of Ea specific bacteriophages in in vitro control of fire blight on pear blossoms. Phage ΦEa6 was isolated from irrigation water in 2011, while phages ΦEa8 and ΦEa10 were isolated from rhizosphere of apple tree in 2013. The phages were specific to Ea strains isolated from different hosts and localities in Serbia. Phage efficacy was tested by application of 30 µl of phage suspension (108 PFU/ml) respectively on detached pear blossoms, 30 min before application of the inoculum. The blossoms were inoculated by using 30 µl of Ea strain KFB153 suspension (106 CFU/ml) on ten blossoms per treatment in four replications. Inoculated but untreated blossoms, those treated with streptomycin (100 ppm) or with sterile distilled water were used as controls. Disease severity was evaluated 4 and 6 days after inoculation using a rating scale modified from Pusey (1999), and statistically analyzed by ANOVA and Duncan's multiple range tests. The results showed that all phage treatments significantly reduced symptoms development compared to the untreated control. However, there was statistically significant difference in efficacy among different phage strains treatments. Phages ΦEa6 and ΦEa8 reduced disease severity by 11% and 24 %, respectively. The most efficient was strain ΦEa10 which reduced disease severity by 95% compared to the untreated control. There was no statistically significant difference in efficacy of this treatment and streptomycin treatment, used as standard. High efficacy of phage ΦEa10 to reduce fire blight symptoms in vitro, makes this strain a good candidate for future use in biocontrol of the fire blight.