2019 ASHS Annual Conference

Apples production relies on grafting separate scion and rootstock genotypes together to enable the rootstock to confer productivity characteristics and disease resistance onto the scion. Although the effects of the rootstock on scion health and productivity are reasonably well-understood, the impacts of the scion on the rootstock are relatively unexplored, especially in terms of potential impacts of scion-specific photosynthate quantity and composition. This study assesses the impacts of apple scion cultivars on root exudates and the corresponding rhizosphere microbiome. In a greenhouse experiment, biochemical compounds released by tree roots within the first growing season were shown to differ according to the scion cultivar bud-grafted on the apple rootstock. Cultivar-based differences were more profound in metabolites with potential to inhibit pathogen growth than in metabolites that would promote overall microbial growth in the root-zone. Interestingly, apple scion cultivar did not have a detectable cultivar-based effect on the root-zone microbial community during the first two seasons of growth after bud-grafting, using the same scion and rootstock cultivars. Results additionally indicated that environmental factors, especially temperature and water relations, also impact apple root exudates, both quantitatively and qualitatively. Methodology for plant management, metabolic profiling, rhizosphere microbiome assessment, and data analysis will be discussed. Furthermore, lab resources, experimental design, and sample collection for performing this type of research through “science by mail” will be detailed.