B. Franz Lang

Societal impact statement This investigation addresses the diversity of microbial endosymbionts in cranberry, which are among the least understood and ill‐defined ericoid symbionts. There is excellent potential for Ericaceous plants, such as cranberry and blueberry, to be farmed more sustainably once the properties and functioning of their associated microbiomes are known in more detail. Here, we demonstrate that some bacterial and fungal endosymbionts of cranberry stimulate plant growth and suppress fungal pathogens. They have the potential for field applications as a first step toward sustainable cranberry farming. Summary Virtually, all vascular plants harbor bacterial and fungal endosymbionts, which colonize predominantly but not exclusively, roots. Most common among fungal partners are arbuscular mycorrhizal fungi (AMF; Glomeromycotina) that live within plant roots and provide soil nutrients to the plant while receiving from the plant organic carbon sources. Ericaceae are an exception as they do not host AMF but rather the taxonomically ill‐defined “ericoid mycorrhizal fungi,” including select ascomycete and basidiomycete species. Because the diversity of endosymbionts in Ericaceae is poorly investigated, we set out to explore the microbiome of Vaccinium macrocarpon Aiton (cranberry). Here, we report the isolation and ribotyping of ~180 distinct bacterial and fungal endophytes collected from roots, stems, and leaves of cranberry plants cultivated in Quebec, Canada. Plant growth promotion was assessed after inoculating plant cuttings with these microbes, whereas pathogen suppression was tested on agar plates by growth confrontation. We show that the cranberry microbiome varies substantially between tissues, cultivars, and across fields of the same farm. Among the isolates, 16 bacterial and 8 fungal strains exhibit biofertilization or biocontrol properties with potential application in sustainable cranberry farming. We propose to move towards a more rigorous, molecular‐based definition of ericoid mycorrhiza, accounting for their broad evolutionary and morphological diversity.