Dynamics of endophytic bacteria in plant in vitro culture: quantification of three bacterial strains in Prunus avium in different plant organs and in vitro culture phases

Endophytic bacteria occurring in plant in vitro cultures have often been described as contaminants, although these are generally present in all plant tissues, often with plant growth promoting effects. The effects of bacterial endophytes in different in vitro culture phases and in different plant organs of Prunus avium were studied. In a previous study we investigated the endophytic bacterial community of six registered silvaSELECT(A (R)) genotypes and found differences in the bacterial community that correlated with propagation success. In this study, quantitative polymerase chain reaction protocols were developed to look at the dynamics of the most abundant endophytes, Mycobacterium spp., Rhodopseudomonas spp., and Microbacterium spp. These endophytes were quantified during propagation and rooting, and the bacterial content in three successive years was evaluated depicting the fluctuation over time. Leaves, stems, and shoots were found to contain bacteria although in different abundance. It was shown that after regeneration via adventitious shoots the bacteria were not eliminated, but showed slightly modified concentrations. The plant growth promoting traits of the two isolates Rhodopseudomonas palustris N-I-2 and Microbacterium testaceum D-I-1 were tested in an inoculation experiment, and showed a promotion in rooting of two difficult-to-propagate P. avium genotypes.