Exploring the potential of plant growth promoting endophytes from Piper longum L

Abstract

Medicinal plants are a rich source of bioactive secondary metabolites, which have a huge demand in food, pharmaceutical and cosmetic industries. In this study, we have investigated the endophytic microbiota of Piper longum, an ethnomedicinal plant of Indian subcontinent, which is widely used in Ayurvedic formulations for curing respiratory and digestive disorders. Here, we report the isolation of 67 bacterial and 26 fungal endophytes from different plant parts, namely roots, shoots, and spikes. Interestingly, most of the isolated endophytes produced varying concentrations of indole-3-acetic acid (some producing gt20 µg/ml). Majority of the bacterial endophytes were also found to produce ammonia and siderophores. Besides, some endophytic bacteria were also found to show mineral solubilising and extracellular enzyme activities. Next, 16 endophytic bacterial isolates that exhibited high plant growth promoting (PGP) trait(s) under in vitro conditions and three best IAA producing fungal endophytes were identified by 16S rRNA gene sequencing and ITS sequencing, respectively. Further, the individual inoculation of four bacterial endophytes with multiple (and high) PGP potential, namely Acinetobacter soli S14, Pseudomonas khazarica S34, Bacillus paramycoides S9, and Enterobacter hormaechei R15, was found to enhance seed germination percentage and seedling growth in tomato and wheat. Moreover, inoculation of E. hormaechei and A. soli, remarkably induced adventitious root formation in stem cuttings of P. longum, and higher chlorophyll content and more robust vegetative growth in adult plants. Further, the addition of melatonin to endophyte-treated plants improved stress tolerance potential (showed lesser accumulation of reactive oxygen species, higher proline and phenylalanine content) in P. longum plants. Further, individual inoculation of the three fungal endophytes namely PLR2 (Colletotrichum cobbittiense), PLR18 (Colletotrichum cobbittiense) and PLR10 (Alternaria alstroemeriae) in maize and chickpea under salt stress condition (250 mM NaCl solution) showed better seedling growth in comparison to controls. Altogether, our results provide substantial clues for thorough investigation of the endophytic microbiome from this unexplored plant species for sustainable agriculture and bioprospecting for novel traits. newline