Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2017
Publication Date: 6/19/2017
Citation: Leisso, R.S., Rudell Jr, D.R., Mazzola, M. 2017. Metabolic composition of apple rootstock rhizodeposits differs in a genotype-specific manner and affects growth of subsequent plantings. Soil Biology and Biochemistry. 113:201-214. Interpretive Summary: Apple replant disease (ARD) negatively impacts tree health and reduces crop yield in new orchard plantings established on sites previously grown to the same or related species. Use of tolerant rootstock genotypes can diminish the growth limiting effects of ARD; however, the potential role of genotype-specific rhizodeposits contributing to ARD tolerance has not been intensively examined. This study demonstrates that rhizodeposition differs among rootstock genotypes (G41, G935, M26, M9Nic29) in terms of both quantity and composition, including differences specific to ARD tolerant genotypes (G41 and G935) and ARD susceptible genotypes (M26 and M9Nic29). Specific metabolites differing among genotypes include phloridzin and phloretin soon after planting and benzoic acid and rutin 10-12 weeks after planting. A number of unidentified metabolites also separated ARD susceptible from ARD tolerant rootstocks. Orchard soil pH treated with rhizodeposits differed in a rootstock genotype-specific manner, and seedlings planted in orchard soil treated with rhizodeposits differed in growth, with soil treated with M26 rhizodeposits resulting in greater seedling growth. This study provides novel results in relation to apple root rhizodeposition and serves as the foundation for further work into specific aspects of rhizodeposition as it relates to a variety of root functions and biology, including root disease and tree growth.
Technical Abstract: The percolated rhizodeposit composition and quantity of 4 apple rootstock genotypes grown in sand was examined via liquid chromatography mass spectrometry time-of-flight, specifically contrasting the rhizodeposits of apple replant disease susceptible genotypes (M26, M9Nic29) with apple replant disease tolerant genotypes (G41 and G935). Untargeted phenolic rhizodeposit metabolic profiling indicated that metabolic profiles differed according to rootstock genotype, with G41 and G935 showing the most similarity in the first principal component of multivariate analysis. Numerous of unidentified rhizodeposit compounds differed among rootstock genotypes over the course of the experiment (10 weeks). Of identified compounds, phloridzin and phloretin were highest in ARD-susceptible genotypes M9Nic29 and M26 at the initial assessment (2 weeks after planting) and overall levels decreased over time. Benzoic acid was higher for ARD-tolerant cultivar G935 at the end of both experiments (10 weeks and 12 weeks after planting, respectively), while rutin and kaempferol were higher for the ARD-susceptible cultivar M26 at the end of second experiment (12 weeks). Total quantity of rhizodeposit corresponded to rootstock vigor as measured by root weight and leaf area. Orchard soil spatially separated from the trees and treated with apple rhizodeposits had lower pH than soil collected from no-tree controls. Seedling growth in rhizodeposit treated soils differed according to rootstock genotype in a subsequent bioassay. Differences in metabolite composition of rhizodeposits associated with ARD cultivar tolerance, and temporal dynamics of their production during early stages of rootstock growth following dormancy, offers insight into the potential contribution of genotypic-specific rhizodeposition to ARD tolerance, and provide the basis for studies concerning the function of rhizodeposits.