Reduction of hyperhydricity in tissue cultures of oregano (Origanum vulgare) by extracellular polysaccharide isolated from Pseudomonas spp

Hyperhydricity or vitrification is a physiological malformation affecting tissue culture-based propagation of several plant species. A Pseudomonas spp-mediated approach was recently developed to control hyperhydricity in oregano. This bacterium-induced prevention of hyperhydricity helped the establishment of clonal plants in the greenhouse without extensive acclimatization. The prevention of hyperhydricity was specifically linked to mucoid Pseudomonas spp and was characterized by high chlorophyll and reduced water content in oregano shoots. The focus of research reported in this paper was to purify the extracellular mucoid component from Pseudomonas spp and evaluate the effect on hyperhydricity in oregano tissue culture. The extracellular mucoid component was purified by ethanol precipitation. This extracellular mucoid component was confirmed to be a polysaccharide using gas chromatography-mass spectrometry. The effect of purified polysaccharide to prevent or reduce hyperhydricity was tested in oregano clone 0–1. The polysaccharide prevented hyperhydricity in oregano with reduced efficiency compared to bacterial inoculation. This was characterized by higher chlorophyll and reduced water content when compared to uninoculated/untreated oregano shoots. This confirms that the Pseudomonas spp-mediated hyperhydricity reduction in oregano is partially due to its extracellular polysaccharide. This provides a novel approach to develop a media formulation to control hyperhydricity in wide number of plant species where tissue culture is used for clonal propagation.