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 r esults in excessive hydration, low lignification and reduced mechanica l strength of tissue culture-generated plants. This results in poor re generation of such plants and requires elaborate greenhouse acclimatio n for outdoor growth. A unique mucoid Pseudomonas sp.; strain F that p revented 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 com mercial clonal lines of raspberry (Rubus sp.; CDH-92; GEL-20; Heritage ; JCR-FL) by bacteria (Pseudomonas sp.; F strain). Acclimation was enh anced in CDH-92, GEL-20 and to a lesser extent in JCR-FL. Such bacteri a-treated clones adapted easily to outdoor or greenhouse conditions. T hirty days after the initial Pseudomonas inoculation (first cycle), cl onal lines GEL-20 and Heritage had reduced water content. All four clo nal lines were subcultured without re-inoculation over five 30-day cyc les carrying the Pseudomonas inoculation from the first cycle. At the end of these five 30-day cycles, the water contents of all clonal line s were significantly lower. After 2.5 months of performing the initial inoculation and prior to the acclimation testing stage, all treated c lonal lines except CDH-92 had higher levels of total phenolics compoun ds and chlorophyll. These results further confirm the role of non-spec ific plant or rhizosphere-associated, polysaccharide-producing bacteri a, in imparting enhanced vigor and stress tolerance in tissue culture- generated plants. This information can be used for rapid acclimation o f economically important, tissue culture-generated plant clones to out door environments. (C) 1998 Elsevier Science Ltd. All rights reserved.