Drought tolerant Methylobacterium populi (Nel-c) enhanced growth and disease resistance in amaranth

Pink Pigmented Facultative Methylotrophs (PPFM) is important for growth promotion and stress tolerance in plants and can also stimulate induced systemic resistance against plant pathogens. PPFMs were isolated from amaranth leaves of ten major locations of amaranth in Thrissur district of Kerala. Under in-vitro, Seven PPFM isolates were positive for IAA production with highest production by Kod-c isolate (15.03 μg ml-1).The isolate Pat-c showed highest nitrogen fixation of 0.766 mg g-1. The amount of phosphate solubilization ranged from 5.99 to 11.15%. Eight isolates were positive for ACC deaminase activity. Three isolates (Kod-c: 62.7%, Kan a: 45.7% and Nel-c: 48.9%) inhibited Rhizoctonia solani, out of 10 isolates. Eight PPFM isolates were positive for ammonia production and none produced hydrogen cyanide and siderophore under in-vitro conditions. Nel-c PPFM isolate was tolerant to pH 3.5 and Nel-c and Kan-a isolates were tolerant to 20% PEG induced water stress. The three most promising PPFM isolates were identified as Methylobacterium sp. (Kod-c and Kan- a) and M. populi (Nel-c) using 16S rRNA sequencing. The three PPFM isolates significantly increased plant height, number of leaves, days taken for first flowering and weight of fresh shoots when compared to uninoculated plants. Disease severity was also lowest (54.08%) in the case of M. populi (Nel-c). The present study revealed that M. populi (Nel-c) isolate was the most promising stress tolerant native PPFM isolate for growth promotion and disease management in amaranth.