Niche-Based Priority Effects Predict Microbe Resistance toErwinia amylovorain Pear Nectar

Abstract

ABSTRACTFire blight is a devastating disease affecting pome fruit trees that is caused byErwinia amylovoraand leads to substantial annual losses worldwide. While antibiotic-based management approaches like streptomycin can be effective, there are concerns over evolved resistance of the pathogen and non-target effects on beneficial microbes and insects. Using microbial biological control agents (mBCAs) to combat fire blight has promise, but variable performance necessitates the discovery of more effective solutions. Here we used a niche-based predictive framework to assess the strength of priority effects exerted by prospective mBCAs, and the mechanisms behind growth suppression in floral nectar. Throughin vitroandin vivoassays, we show that antagonist impacts on nectar pH and sucrose concentration were the primary predictors of priority effects. Surprisingly, overlap in amino acid use, and the degree of phylogenetic relatedness between mBCA andErwiniadid not significantly predict pathogen suppressionin vitro, suggesting that competition for limited shared resources played a lesser role than alterations in the chemical environment created by the initial colonizing species. We also failed to detect an association between our measures ofin vitroandin vivo Erwiniasuppression, suggesting other mechanisms may dictate mBCA establishment and efficacy in flowers, including priming of host defenses.