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ISHS Acta Horticulturae 1056: XIII International Workshop on Fire Blight

STRATEGY FOR NON-ANTIBIOTIC FIRE BLIGHT CONTROL IN U.S.-GROWN ORGANIC POME FRUIT

Authors:   K.B. Johnson, T.N. Temple, R.B. Elkins, T.J. Smith
Keywords:   Malus × domestica, Pyrus communis, fire blight, Erwinia amylovora, biocontrol, copper bactericide, fruit load thinning, lime sulfur, loop-mediated isothermal amplification
DOI:   10.17660/ActaHortic.2014.1056.12
Abstract:
Pome fruit produced organically under the United States Department of Agriculture National Organic Program (NOP) standard can be treated with streptomycin or oxytetracycline for fire blight suppression, but a recent NOP regulatory review set a 2014 phase out date for these materials. In response, we employed a systems approach to development of non-antibiotic programs for fire blight control in the western United States. Objectives were to: 1) understand the effect of sanitation (i.e., a copper spray at the delayed dormant stage of growth) on pathogen presence in flowers; 2) quantify the impact of fruit load thinning materials on pathogen and biocontrol agent populations in flowers; and 3) develop integrated biocontrol programs where registered products are utilized at specific stages of flowering based on their relative ability to suppress the pathogen on the floral stigmata or in the floral cup. Under Objective 1, positive effects of copper-based sanitation on pathogen presence in flowers was observed by utilizing a molecular assay termed ‘loop mediated isothermal DNA amplification’ (LAMP), which in the future could be available as an on-site decision aid. Experiments under Objective 2 demonstrated that the fruit load thinning material, lime sulfur, reduced flowers potentially infected by E. amylovora and also suppressed bacterial growth in flowers, and therefore compressed the time in bloom when other materials are needed for fire blight control. Under Objective 3, biocontrol programs beginning with a stigma colonizer (e.g., the yeast Aureobasidium pullulans in Blossom Protect) followed by floral cup protectors (also Blossom Protect or a new ‘fruit-safe’ copper material, Previsto) provided significant and consistent fire blight control. For example, over four trials, treatment with Blossom Protect after lime sulfur reduced the incidence of fire blight by an average of 92% compared with water only. Similarly, Blossom Protect at 70% bloom followed by Previsto at full bloom reduced the incidence of fire blight by an average of 88% compared with water only. These levels of control were similar statistically to treatment with the antibiotic, streptomycin.
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