Podolich O. Interaction of endophytic bacteria with potato plants.

This manuscript is devoted to studying interaction of endophytic bacteria with potato plants, as well as endophytes influence on plant growth and systemic resistant to phytopathogen. A detailed knowledge of the life-style of endophytes is essential for developing endophytic biofertilizers and biocontrol agents. Our results suggest that potato supports a diverse bacterial endophytes. The community composition of the culturable component of the microflora was remarkably different from that revealed by culture-independent method. Introduction of rhizobacterium Pseudomonas fluorescens IMBG163 into potato plant tissue resulted in essential rise of endophytic bacterial species number, however, in the further micropropagation of plants their number was reduced. Endophytic isolates from potato varieties Zagadka and Nigru, induced by the rhizobacterium, exhibited beneficial for plant characters. Some bacterial endophytic isolates showed their ability to biocontrolling of phytopathogens, either through direct antagonism of pathogens (Erwinia carotovara subsp. atroseptica and Pseudomonas syringae pv. syringae) or by inducing systemic resistence of plants to pathogens (Pseudomonas syringae pv. tomato DC3000). A bacterial strain utilizing methanol was isolated from the roots of potato in vitro plants after induction of endophytic bacterial community by inoculation with P. fluorescens IMBG163. This isolate M1 was characterized by partial 16S rRNA sequence analysis which showed high sequence similarity to the sequence of Methylobacterium radiotolerans. Two molecular methods were used for localizing methylobacteria in potato plantlets: PCR and in situ hybridization (ISH/FISH). A PCR product specific for the Methylobacterium genus was found in DNA isolated from the surface-sterilized plantlet leaves. Presence of Methylobacterium rRNA was detected by ISH/FISH in leaves and stems of inoculated as well as axenic potato plantlets although the bacterium cannot be isolated from the axenic plants. Thus, M. radiotolerans IMBG290resides in unculturable state within tissues of in vitro-grown potato plants and becomes culturable after inoculation with P. fluorescens IMBG163. Inoculation of potato plantlets with the M. radiotolerans IMBG290 increased stem height of potato plantlets and plant biomass when compared to controls. Also the carbohydrate and fat content of the shoots of endophyte-inoculated potato plants was higher than in the controls. Specific reaction on production of indole-acetic acid by M. radiotolerans IMBG290 was negative but the biotest with cucumber etiolated cotyledons demonstrated its capacity of producing cytokinins. Therefore, cytokinins were considered a means for the M. radiotolerans to directly influence plant metabolism. Therefore M. radiotolerans IMBG290 may offer much potential as the basis for new biostimulators of plant growth and biocontrol agents along with other endophytes isolated from potato tissue culture which exhibited beneficial for plant characters.