The Influence of Host Genotypes on the Endophytes in the Leaf Scar Tissues of Apple Trees and Correlation of the Endophytes with Apple Canker (Neonectria ditissima) Development

Abstract

Bacterial and fungal endophytes may help their host in terms of improved tolerance to abiotic and biotic stresses and enhanced growth. European apple canker, caused by Neonectria ditissima, is widespread in apple-growing regions. Infection by N. ditissima occurs through artificial or natural wounds, including leaf scars, picking wounds, and pruning cuts. Using F1 progeny trees in an experimental orchard derived from a cross between a canker-susceptible genotype and a canker-tolerant or -resistant genotype, we assessed both bacterial and fungal endophyte communities in apple leaf scars, and determined correlations of endophytes with canker development. All trees were artificially inoculated with an N. ditissima isolate postplanting. Specific components of apple endophytes as well as a number of individual fungal or bacterial groups in leaf scars were partially genetically controlled by host genotypes. Several bacterial groups were significantly correlated with canker-related traits, mostly positively associated with canker tolerance. A few fungal groups may facilitate canker development whereas others may compete with canker. However, most of these microbial groups could not be identified to the species level with confidence; even for those groups which could be assigned to the species level, there is insufficient knowledge about their ecological characteristics in relation to plants. The present results may be used to inform further research using biocontrol to manage N. ditissima and breeding for resistance.