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Field efficacy of systemic acquired resistance inducers for fire blight management and pathogenesis-related protein gene expression in Malus domestica

Rachel Kreis: North Carolina State University

<div>Fire blight on apple caused by <em>Erwinia amylovora</em> can be a significant problem for apple growers causing blossom and shoot blight. Application restrictions and resistance concerns associated with streptomycin and other antibiotics, necessitate the evaluation of alternative products for fire blight control. Products including Lifegard (<em>Bacillus mycoides</em> isolate J), Actigard (acibenzolar-S-methyl), and MBI-10612 (Marrone Bio Innovations) that induce systemic acquired resistance (SAR) were evaluated for efficacy against fire blight and for pathogenesis-related (PR) protein gene expression. Treatments were applied at 20%, 40%, 80%, and full bloom on <em>Malus x domestica </em>‘Rome Beauty’ in 2017. Treatments with SAR inducers resulted in significantly less blossom blight than the untreated control (UTC) and the Lifegard treatment resulted in significantly less shoot blight than the UTC. PR protein gene expression was evaluated in apple blossoms 24 h and 7 days after initial applications and evaluated in leaves 24 h, 7 days, and 5 weeks after initial application. The PR-1 gene was found to be 1.23 and 1.17 times greater in leaf and blossom tissue respectively after 24 h of treatment with Lifegard than the UTC. Gene expression of PR-1 was also 1.58 and 2.09 times higher in the leaves and blossoms 7 days after treatment with Lifegard and 2.58 times greater after 5 weeks. Further work is being done to compare PR gene expression in other treatments with PR-1, PR-2, and PR-8.</div>