Inoculation with native bacterial endophytes promote adventitious rooting and plant growth in Piper longum L.

Piper longum, the Indian long pepper, is widely used in Ayurvedic medicine system to cure respiratory and digestive disorders. In a previous study, we reported the isolation and characterization of plant growth promoting (PGP) endophytic bacteria from P. longum. Here, we have tested the effect of two native endophytic bacteria, Acinetobacter soli PlS14 and Enterobacter hormaechei PlR15, on growth attributes, adventitious root development and reactive oxygen species levels in P. longum PlR15. Our results indicate that stem cuttings treated with A. soli PlS14 and E. hormaechei PlR15 exhibited rooting in > 50% of stem cuttings, when none of the Control cuttings did. Further, the endophyte-inoculated plants showed better vegetative growth (in terms of shoot growth and leaf number); higher levels of chlorophyll, proline and phenylalanine ammonia lyase; and lesser accumulation of reactive oxygen species than Control plants. The improved growth performance of endophyte-inoculated plants could be corelated with results of localization studies that indicate higher bacterial population in roots of endophyte-inoculated plants. To our knowledge, this is the first report of use of native endophytic strains as bioinoculants for growth of P. longum. Altogether, our results highlight the (often neglected) role of PGP native endophytes for cultivation of plants including medicinal plant species.