Distribution of streptomycin-resistant strains of Erwinia amylovora in Israel and occurrence of blossom blight in the autumn

Following failure in control of fire blight with streptomycin, the distribution of streptomycin-resistant strains of Erwinia amylovora in Israel was surveyed. During 1994-1997 109 pear, apple, loquat and quince orchards were monitored. Streptomycin-resistant strains of E. amylovora were recovered from flowers and from infected branches collected at 18 locations in the Sharon, Galilee and Golan Heights regions. In the Sharon region all the isolated strains of E. amylovora were streptomycin-resistant, whereas in the Galilee and Golan Heights, resistant as well as sensitive E. amylovora strains were recovered at different locations. In the southern coastal plain no resistance could be detected. Streptomycin-resistant strains of E. amylovora did not hybridize with the DNA probe SMP3, and resistance could not be transferred by mating to a sensitive strain, suggesting that streptomycin resistance in Israel is not plasmid-mediated. Fire blight symptoms were observed, for the first time, on pear blossoms during the autumn of 1994. A high population of 2 x 10(6)-6 x 10(7) CFU/flower in the autumn of 1995 and of 1996 was correlated with the appearance of blossom blight symptoms.