Reduced hyperhydricity and enhanced growth of tissue culture-generated raspberry (Rubus sp.) clonal lines by Pseudomonas sp. isolated from oregano

Hyperhydricity or vitrification is a physiological malformation that results in excessive hydration, low lignification and reduced mechanical strength of tissue culture-generated plants. This results in poor regeneration of such plants and requires elaborate greenhouse acclimation for outdoor growth. A unique mucoid Pseudomonas sp.; strain F that prevented hyperhydricity in tissue culture-generated oregano (Origanum vulgare) shoot clones was recently isolated in this laboratory. Based on this study we have now tested hyperhydricity prevention in four commercial clonal lines of raspberry (Rubus sp.; CDH-92; GEL-20; Heritage; JCR-FL) by bacteria (Pseudomonas sp.; F strain). Acclimation was enhanced in CDH-92, GEL-20 and to a lesser extent in JCR-FL. Such bacteria-treated clones adapted easily to outdoor or greenhouse conditions. Thirty days after the initial Pseudomonas inoculation (first cycle), clonal lines GEL-20 and Heritage had reduced water content. All four clonal lines were subcultured without re-inoculation over five 30-day cycles carrying the Pseudomonas inoculation from the first cycle. At the end of these five 30-day cycles, the water contents of all clonal lines were significantly lower. After 2.5 months of performing the initial inoculation and prior to the acclimation testing stage, all treated clonal lines except CDH-92 had higher levels of total phenolics compounds and chlorophyll. These results further confirm the role of non-specific plant or rhizosphere-associated, polysaccharide-producing bacteria, in imparting enhanced vigor and stress tolerance in tissue culture-generated plants. This information can be used for rapid acclimation of economically important, tissue culture-generated plant clones to outdoor environments. (C) 1998 Elsevier Science Ltd. All rights reserved.