Functional Pink Pigmented Facultative Methylotrophs from Capsicum frutescens Phyllosphere as Bioinoculants for Growth Promotion and Drought Stress Alleviation in Chilli

Phyllosphere microorganisms including pink-pigmented facultative methylotrophs (PPFMs) play a vital role in alleviating biotic and abiotic stresses by enhancing plant growth, resilience, and nutrient availability. Our study focused on identifying and characterizing PPFMs from bird's eye chilli (Capsicum frutescens), a hardy crop with tolerance to drought, pests and diseases. Their potential in enhancing growth and drought tolerance in chilli (Capsicum annuum) was explored under pot culture. PPFM colonies isolated from the phyllosphere of bird's eye chilli were screened in vitro for plant growth promoting traits. Isolate Methylorubrum thiocyanatum CF7 demonstrated the highest IAA (18.26 µg mL−1) and GA (22.07 µg mL−1) production. Isolate Methylorubrum podarium CF15 had the maximum extra cellular ammonia production (10.06 µmol mL−1) and Methylobacterium gregans PPFM 38 (reference culture) showed the highest 1‑aminocyclopropane-1-carboxylic acid (ACC) deaminase activity (19.35 µmol of α‑ketobutyrate produced per mg of protein per hour), followed by M. thiocyanatum CF7 (14.08 µg mL−1). All selected isolates tolerated up to 30% Poly Ethylene Glycol (PEG) 6000 (w/v) in the medium. Three superior isolates viz. CF6, CF7 and CF15 were identified as Methylorubrum populi, Methylorubrum thiocyanatum, and Methylorubrum podarium by 16SrRNA sequencing. Application of 1% PPFM culture by seed treatment and foliar spray significantly enhanced plant growth parameters of chilli. When irrigation was withdrawn 15 days after a foliar spray with PPFM, the treated plants remained turgid for upto six days while the plants in the control group wilted on the fourth day of irrigation withdrawal. Physiological parameters like cell membrane integrity, relative water content, proline, activity of super oxide dismutase (SOD) and peroxidase also improved in PPFM treated plants. The results suggest that application of PPFMs through seed treatment and foliar spray can effectively improve growth and drought tolerance in chilli plants.