- SCAB AND FIRE BLIGHT OF APPLE 383
screen for. More recently, the first gene-for-gene interaction between
E. amylovoraandMalus×robusta5 was identified (Vogt et al. 2013).
This resistance trait was shown to be highly effective in preventingE.
amylovorainfection. Indeed, this source of resistance has been incorpo-
rated into a number of dwarfing rootstocks for apple production, and in
particular, those from the Cornell Geneva rootstock breeding program
(Fazio et al. 2015). Fire blight resistance in rootstocks is important, in
that this resistance will at least prevent fire blight infection from killing
the entire tree. However, examination of a collection ofE. amylovora
isolates already identified a mutation in approximately 5% of the iso-
lates that had broken the resistance (Vogt et al. 2013). An additional
source of resistance yet unidentified was observed in two other species,
M. baccataandM. fusca(Vogt et al. 2013). These results suggest that
the potential for breeding for fire blight resistance is a long-term, dif-
ficult proposition. The generation of apple clones using transgenic or
cis-genic approaches have been successful in introducing fire blight tol-
erance to highly susceptible varieties such as “Gala” (Borejsza-Wysocka
et al. 2007), but these lines may never be commercialized because of
consumers’ negative perceptions toward GMOs (Hu et al. 2004).
IV. CONCLUSIONS AND FUTURE TRENDS
The management of apple diseases in all but the most arid of climates is
complex. Unfortunately, a false trichotomy has pit proponents of GMOs,
proponents of organic agriculture, and the practitioners of conventional
agriculture against each other and the public, regarding what is, and
what is not sustainable. None of these three approaches alone will result
in sustainable apple production for the 21st century. However, taken
together, all three of these systems can contribute to a better disease
management paradigm that is predicated on cultivars that require fewer
pesticide inputs, the judicious use of chemical controls, and cultural
practices that reduce pathogen inoculum. No single approach will meet
the needs and address all the concerns of an ever-expanding public that
will continue to demand fresh fruit.
Genetically modified apples, although posited as an answer, oversim-
plify a complex management problem. Even if accepted by the public,
they will face resistance breakdown (possibly further eroding public
trust in scientists), just asVf-resistant cultivars already have. Microbial
populations are too large and too diverse for any one tactic to serve as a
silver bullet. And the incorporation of GMOs into apple production is
unlikely anytime soon, due to issues of public acceptance. The recent