380 J.L. BECKERMAN AND G.W. SUNDIN
illustrates the risks growers face in maximizing economic returns. This
problem continues, as traits selected for by apple breeders for more
recently released varieties are focused on eating quality, other sensory
evaluations, and storage characteristics rather than fire blight suscepti-
bility. Thus, the major investment growers make with each new high-
density planting of fire blight susceptible cultivars could be wiped out
within one season by a fire blight epidemic. Cultivars do exist with
reduced susceptibility or tolerance to fire blight; however, modern con-
sumer preference does not favor these fire blight resistant cultivars (e.g.,
“Red Delicious” and “Golden Delicious”).
C. Antibiotic Use for Fire Blight Management and Antibiotic
Resistance
The blossom blight phase of fire blight has been the primary target of
chemical intervention attempts since this is considered the site of pri-
mary infection. Of all materials currently available for management of
blossom blight, the antibiotic streptomycin is by far the most effective
in the eastern and midwestern United States. (reviewed in Ngugi et al.
2011). Streptomycin has been a mainstay for fire blight management
in the United States, since the 1950s (McManus et al. 2002), and has
been utilized heavily for several decades. In fact, the effective use of
streptomycin was a success story that enabled the production of highly
susceptible apple cultivars for decades in many regions of the United
States.
Unfortunately, the excellent efficacy of streptomycin also led to its
downfall. Because streptomycin was so effective for fire blight control,
growers started using this compound more frequently during bloom,
and also applied streptomycin later in the season for shoot blight
control with some growers using 10 or more applications per season.
It is believed that this reliance and overuse of streptomycin for fire
blight control resulted in the evolution of streptomycin-resistant (SmR)
strains ofE. amylovorain California by 1971 and in Washington and
Oregon by 1972 (reviewed in McManus et al. 2002). SmRE. amylovora
strains were first isolated in Michigan in the southwestern region of the
state in 1991 and have since been detected in other regions of the state
(Chiou and Jones 1993; McGhee et al. 2011), and were isolated in New
York in the 2000s (Russo et al. 2008). Thus, as with highly effective
fungicides such as the SBIs for scab control, the successful deployment
of a compound for disease control ultimately led to its downfall through
misuse, overuse, and increased selection on pathogen populations that
drove evolution toward antibiotic resistance.