Identification and pathogenicity of Raoultella and Pseudomonas species associated with roots of Taraxacum kok-saghyz

Abstract Natural rubber (NR) is a critical raw material essential for the production of thousands different rubber and latex products. In most cases, it cannot be replaced by synthetic rubber alternatives. At the present time, NR is produced solely from a single species, Hevea brasiliensis , which is grown in tropical regions. Several important reasons including the danger that South American Leaf Blight disease might spread to Southeast Asia stimulate the search for alternative rubber producers. One of them, Taraxacum kok-saghyz , attracts particular attention. In this study, performed in an aeroponic phytotron, as well as in vitro culture, we identified two bacteria associated with root rot of the NR-producing plant T. kok-saghyz - Pseudomonas putida and Raoultella terrigena . According to the literature, interaction of these bacteria with plants is described as symbiosis. However, our data suggest that under certain conditions well-characterized endophytic bacteria can act as pathogens. We showed that plants, cured of phytopathogens, demonstrate fast growth rates, even in at high summer daytime temperatures. T. kok-saghyz continued to grow (defoliation did not occur) and to build up a biomass, which may lead to an increase in the accumulation of NR and inulin in the roots. Our research demonstrates that aeroponic cultivation is a promising way to grow T. kok-saghyz , for production of NR and inulin. In this study we show that plant-associated microorganisms are an important factor influencing plant responses to changes in cultivation conditions.