Pink Pigmented Facultative Methylotrophs (PPFMs) improve rooting in black pepper (Piper nigrum L.) cuttings and mitigate drought stress

Black pepper, a major spice cultivated across the globe, is droughtsensitive, and water stress often results in plant fatality. Pink Pigmented Facultative Methylotrophs (PPFMs), the plant growth-promoting phyllosphere bacteria, can induce physiological changes in plants, making them more tolerant to various stresses. PPFMs from phyllosphere of black pepper were isolated, characterized and, screened for plant growth promotion and drought stress mitigation in black pepper. Sixty PPFM isolates were obtained by leaf imprinting and plating on 5 % PEG 6000 amended Methanol Mineral Salts medium. Screening of isolates for plant growth promotion was based on producing indole acetic acid, gibberellic acid, extracellular ammonia and 1-aminocyclopropane-1-carboxylate deaminase activity in vitro. The influence of three best performing isolates, identified by 16SrRNA sequencing as Methylobacterium aerolatum PNPPFM60, Methylorubrum aminovorans PNPPFM59 and Methylorubrum zatmanii PNPPFM44, on growth and establishment of black pepper cuttings was investigated. M. aerolatum PNPPFM60 recorded the highest biometric parameters. After the foliar application on 90th DAP the soil moisture level was maintained at field capacity for 15 days and then irrigation was withdrawn. The control plants showed symptoms of drought after 3 days of withdrawing irrigation while the PPFM treated plants remained green with higher RWC and higher cell membrane integrity till 7th day. The antioxidant enzymes were highest in plants treated with M. aerolatum PNPPFM60. PPFMs could improve growth of black pepper and mitigate drought stress in early stages of establishment of black pepper and has the potential to be developed as a bioformulation.