PREVENTION OF HYPERHYDRICITY IN OREGANO SHOOT CULTURES IS SUSTAINED THROUGH MULTIPLE SUBCULTURES BY SELECTED POLYSACCHARIDE-PRODUCING SOIL BACTERIA WITHOUT REINOCULATION

Previous studies from our laboratory showed that several non-specific, polysaccharide-producing soil bacteria could be effectively used to p revent hyperhydricity. In this study, prevention of hyperhydricity of shoot cultures of oregano clonal line O-1 was investigated over multip le subculture cycles without re-inoculation of shoots. Results clearly indicate that hyperhydricity was prevented in oregano shoot cultures over eight subculture cycles without any re-inoculation after the init ial inoculation with several polysaccharide-producing bacteria in the first cycle. Hyperhydricity-related parameters of subculture cycles 7 and 8, reported in this manuscript, showed that the water content was significantly reduced in response to all bacteria tested. The total ph enolics content, on a fresh-weight and dry-weight basis, was stimulate d significantly by all bacterial treatments except Pseudomonas stutzer i in the seventh cycle. The chlorophyll content was significantly stim ulated in all treatments on a fresh-weight basis in the two subculture cycles. On a dry-weight basis, except for P. stutzeri, the bacterial species tested induced significant increases in chlorophyll content. P lant growth in response to all bacteria was reduced. In spite of growt h reduction, the numbers of shoot nodes available for propagation were not reduced and all the shoot tissues were unhyperhydrated. These res ults also suggested that prevention of bacteria-mediated hyperhydricit y may be linked to survival of bacteria in the stem, which may be carr ied through to the next subculture. Acclimation studies showed that ba cteria-containing shoots performed better and further strengthened the case for use of non-pathogenic, polysaccharide-producing bacteria for hyperhydricity control in commercial plant tissue cultures.