BIOINOCULATION EFFICACY OF PLANT GROWTH-PROMOTING SEED-ASSOCIATED BACTERIA ON MAIZE SEEDLING GROWTH

Plant growth-promoting endophytic bacteria play essential roles in plant growth and they can be used as bioinoculants in place of chemical fertilizers to directly or indirectly enhance plant growth. This study investigated the bioinoculation potential of plant growth-promoting bacteria isolated from maize seeds and evaluated their ability to enhance seedling growth under controlled conditions. Three bacterial isolates were identified and characterized based on morphological, biochemical, and plant growth-promoting (PGP) traits. The ability of the bacterial isolates on the production of IAA was tested by weighing 2 g of peptone, 1 g of sodium chloride (NaCl), 0.02 g of tryptophan into 200 ml of distilled water was weighed and mixed, 9 ml of the solution was measured into test tube and sterile. A loopful of the microorganism was inoculated and incubated for 48 hrs at 30 degree celsius and 4000 rpm for 10 minutes. After centrifugation, 2-3 drops of orthophosphoric acid and 4 ml Salkowski reagent (0.05 L of 35% perchloric acid and 1 ml of 0.5 M FeCl3.6H2O) was added to 2 ml of the supernatant. The mixture was incubated in the dark for 30 minutes. The development of pink colouration indicated IAA production. The hydrogen production ability of the bacterial isolates was tested by weighing 0.8 g of glycine and 3.2 g of nutrient broth was weighed, into 200 ml of sterile distilled water and was sterilized, using an autoclave at 121oCfor 15 minutes. Result revealed that B2 and B3 demonstrated superior abilities in indole-3-acetic acid (IAA) production, phosphate and zinc solubilization, nitrogen fixation, and exopolysaccharide secretion. Additionally, they exhibited tolerance to abiotic stresses such as drought, salinity, and heavy metal exposure, highlighting their resilience in diverse environmental conditions. Quantitative analyses showed enhanced IAA and siderophore production, particularly in B3, while enzyme profiling confirmed the presence of key extracellular enzymes involved in nutrient cycling. Inoculation trials conducted in screenhouse conditions indicated that B2 and B3 significantly improved germination rate, root and shoot biomass, and overall seedling vigor compared to the uninoculated control. The isolates showed diverse plant growth promoting traits, including nutrient solubilization, phytohormone production, biocontrol capabilities, extracellular enzymatic activities, and environmental stress tolerance.