Interaction of hyperhydricity‐preventingpseudomonassp. with oregano (origanum vulgare) and selection of high phenolics and rosmarinic acid‐producing clonal lines

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Abstract
Phenolic metabolites from oregano and related species in the family Lamiaceae are important sources of antimicrobials and antioxidants. The content of phenolic metabolites in oregano and related species are highly variable due to genetic heterogeneity. This genetic heterogeneity is due to the breeding character being influenced by natural cross‐pollination. In order to develop gene pools to improve ingredient quality and quantity genetically uniform shoot‐based clonal lines were isolated using plant tissue culture techniques. Clonal lines were generated from multiple shoots induced by 1 mg/1 benzylaminopurine in standard Murashige and Skoog medium with 3 % sucrose. Under these optimum conditions 7–10 shoots per explant were generated for further clonal propagation or regeneration of plants. Shoot‐inducing hormones like thidiazuron and adenine sulfate did not improve multiple shoot‐forming ability. Individual shoots of several individual clonal lines with each originating from a single heterozygous seed were then inoculated with a novel Pseudomonas sp. Following 30 days of growth on hormone‐free Murashige and Skoog medium, morphology, tolerance to Pseudomonas, phenolics and rosmarinic acid content were measured and compared to uninoculated controls in 7 clonal lines of oregano. Results indicate that Pseudomonas sp.‐mediated stimulation of phenolics and rosmarinic acid in various oregano clonal lines were directly correlated to tolerance to Pseudomonas sp.. Among these clonal lines, OM‐1 had the highest increase in phenolics and rosmarinic acid with corresponding enhanced tolerance to Pseudomonas sp.. This provides an unique strategy to isolate high phenolics‐producing, genetically uniform clonal lines using Pseudomonas sp.. From a basic research perspective such clonal lines are essential for characterization of biochemical pathways of specific phenolic metabolites. From an applied research perspective, selection of elite clonal lines serve to provide extracts with uniform phenolic ingredients for use as antioxidants and antimicrobials in food systems.