Comparison of IAA Production by Shallot Rhizosphere Isolated Bacteria in Solid and Liquid Media and Their Effect on Shallot Plant Growth

Some of free-living rhizobacteria were isolated from rhizosphereof shallot growing in two different fields on Sulawesi Island. The bacterial isolates were cultured in liquid and solid media and were further tested for their ability to produce bioauxin. L-Tryptophan as a physiological precursor of auxin was added to the culture media and the production of IAA was tested using a colorimeter method. Six isolates from west Sulawesi and ten isolates from South Sulawesi were found to produce bioauxin, while 40 other isolates had negative results on IAA production. The amount of IAA produced by the isolates on liquid medium ranged from 4.01 to 8.62 ppm, while in the solid medium, the concentration of IAA produced by the same bacteria was considerably lower than in Liquid media. Thus, culture conditions influence the secretion of IAA by the bacteria. Of these 16 IAA producing isolates, five efficient producers were used for in plant a growth promotion assay. The isolate MK6-1-1 showed the best stimulatory effect on leaves number and bulb tillers, isolate LB8 was investigated to modulate better bulbs fresh biomass weight, while isolate MK11 was found to have the best effect on bulbs dry weight and bulbs dry biomass weight. Application of liquid media MK 6-1-1 bacteria isolates on the medium shallot planting early phases provides the best results on the vegetative growth of shallot that is leafs number (10.75 pieces) and the number of bulb tillers (2.75 bulbs) except the best plants height showed by Isolate bacteria MK 11 (29,60 cm). Bacterial isolates LB 8 shows bulbs fresh biomass weight (9.83 g) and bulbs fresh biomass shrinkage (7.45) while the bacteria Isolate MK 11 showed the best result of bulb dry weight (2.26 g) and bulbs dry biomass weight (3.41).