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Trunk-injected potassium phosphites and acibenzolar-S-methyl induce SAR in apple trees allowing control of fire blight (Erwinia amylovora)
S. G. AĆIMOVIĆ (1), Q. Zeng (1), G. C. McGhee (1), J. C. Wise (1), G. . Sundin (1). (1) Michigan State University, East Lansing, MI, U.S.A.

Trunk injection of Systemic Acquired Resistance (SAR) inducers as an <i>in planta</i> delivery approach could enhance their effect in fire blight control. PR-protein gene expression indicating SAR should be achieved after injection of SAR inducers on mature apple trees. After 1-2 injections of acibenzolar-S-methyl (ASM; Actigard) or two injections of potassium phosphites (PJ; Phosphojet), using 4 replicates per treatment, inoculated Gala trees were evaluated for blossom and shoot blight and for PR-protein gene expression in leaves and flowers. In year 1, ASM and PJ significantly reduced blossom blight incidence by 37.7-42.2% and 55.9%, respectively. Shoot blight incidence was reduced 70.8% by PJ only. In year 2, ASM and PJ reduced blossom blight by 19.1-21.1% and 25.1%, respectively, and shoot blight by 27-31% and 23.4%, respectively. In year 2, PJ significantly upregulated expression of the PR-1, PR-2 and PR-8 protein genes. ASM upregulated these genes in leaves consistently, in both years. Thus, injected PJ and ASM induce SAR in leaves on mature apple trees but at different times and with different persistence of the effect. SAR activity was not detected in flowers, probably due to reduced accumulation of injected compounds in them, which was driven by their lower transpiration compared to the leaves. With proper dosing and more time for translocation and accumulation in the canopy, trunk-injected SAR inducers could serve as an effective option for fire blight control.

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