amylovora ( Chiou and Jones, 1993 Sundin et al., 1995).
Research shows that when non-target bacterial populations are exposed to broadcast applications of streptomycin in the agroecosystem, resistance genes can be selected, and can then be transferred to target pathogens, such as E. amylovora with resistance to the antibiotic streptomycin, limiting the efficacy of this compound as a plant disease control agent ( Chiou and Jones, 1993 McGhee and Sundin, 2011). An added difficulty in fire blight management is the occurrence and spread of strains of E. In Washington and northern Oregon, economic losses on pome fruits due to fire blight were over $68 million ( Stockwell et al., 2002).Ĭontrol of fire blight is difficult because currently there are no available synthetic compounds with systemic properties that directly affect the pathogen and that could improve fire blight protection programs. In Michigan, a fire blight epidemic in 2000 resulted in economic losses of $42 million due to removal of approximately 400,000 apple trees ( Longstroth, 2001). In the USA, fire blight losses and control costs per year are estimated to be more than $100 million ( Norelli et al., 2003). Yearly losses due to fire blight can be substantial in many countries worldwide. (1920) is a devastating bacterial pathogen of plant species in the Rosaceae family, causing the disease fire blight. With the development of injectable formulations and optimization of doses and injection schedules, the injection of protective compounds could serve as an effective option for fire blight control.Įrwinia amylovora (Burrill 1882) Winslow et al. ASM and PH suppressed fire blight even after cessation of induced gene expression. The time separating SAR induction and fire blight symptom suppression indicated that various defensive compounds within the SAR response were synthesized and accumulated in the canopy. Injection of both ASM and PH resulted in the significant induction of PR-1, PR-2, and PR-8 protein genes in apple leaves indicating induction of systemic acquired resistance (SAR) under field conditions. Trunk injection of oxytetracycline resulted in excellent control of shoot blight severity, suggesting that injection is a superior delivery method for this antibiotic. Overall disease suppression with streptomycin was lower than typically observed following spray applications to flowers. In field experiments, after 1–2 apple tree injections of either streptomycin, potassium phosphites (PH), or acibenzolar- S-methyl (ASM), significant reduction of blossom and shoot blight symptoms was observed compared to water injected control trees. Trunk injection could decrease antibiotic usage in the open environment and increase the effectiveness of compounds in fire blight control.
Trunk injection is a target-precise pesticide delivery method that utilizes tree xylem to distribute injected compounds. Even though successful in control, preventive antibiotic sprays also affect non-target bacteria, aiding the selection for resistance which could ultimately be transferred to the pathogen Erwinia amylovora.
Management of fire blight is complicated by limitations on use of antibiotics in agriculture, antibiotic resistance development, and limited efficacy of alternative control agents.
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