S04 - Session O1 - Bioregulation of adventitious root induction by metabolites secreted from Plant Growth-Promoting Pantoea agglomerans strains -

Authors: Caterina Valerio *, Gabriele Medori, Francesca Luziatelli, Francesca Melini, Lorenzo Gatti, Maurizio Ruzzi, Rosario Muleo, Ivano Forgione

Adventitious rooting (AR) is a crucial part of the agamic propagation of woody plants to obtain a high-quality root system. The process is regulated by several endogenous and exogenous factors such as hormones, light and mineral nutrition. Auxins play a central role and activate the pathways involved in the major morphological and molecular changes of AR. Currently, adventitious roots are mainly induced with IBA, a synthetic auxin, but there is an increasing interest in finding natural alternatives to this product. This study evaluated the effect of metabolites secreted by Pantoea agglomerans on the induction and initiation phase of adventitious rooting in vitro in microcuttings of Pyrus communis var. Dar Gazi , using IBA as a control (CK). P. agglomerans is a Gram-negative plant growth-promoting bacterium (PGPB), which produces indole-3-acetic acid in secreted form when grown in medium supplemented with tryptophan. Tests were performed with quantities of the finished culture medium of P. agglomerans to achieve a final auxin concentration in the rooting medium of 0.2 mg L -1 and 1 mg L -1 . Explants were sampled after four and seven days from the start of treatment (DAT), between 8 and 12 DAT for Pantoea-treated explants (time of root appearance) and at 35 days for CK-explants (time of root appearance ) . The results indicate a different regulation of physiological and phenotypic events generated in microcuttings after bacterial treatment: reduction in the time of appearance of roots, the origin of roots directly from the tissue of the stem microcuttings, and absence of callus development, associated with a decrease in the average number of roots, although they were on average longer than those generated in IBA-treated microcuttings. A qRT-PCR analysis was performed on genes belonging to the WOX, IAA/Aux, and ARF families and on miRNA 156, 160, and 167. The molecular results confirmed that bacterial metabolites played a role in the induction of the AR process, and that the time scale of gene expression was coherent with the reduction of time of root appearance.