Assessment of the Potential of Indole-3-Acetic Acid Producing Bacteria to manage Chemical Fertilizers Application

Indole-3-acetic acid (IAA) has a vital role in stimulation of root growth and nutrients acquisition from soil. The study was conducted to isolate rhizospheric (R) and endophytic (E) IAA producer bacteria from the rhizosphere soil and surface sterilized root of wheat, and evaluate the effects of isolates to managing of chemical fertilizers application. For this, we examined the influence of different chemical fertilizer application rates (40, 60, 80 and 100%) coupled with R (Bacillus toyonensis) and E (Pseudomonas mosselii) IAA producer bacteria on wheat growth. Results indicated that supplementing 80% of the recommended chemical fertilizers rate with E isolates resulted in increase of wheat growth indices, which were similar to 100%-fertilizer need without bacterial inoculant. It seems that application of reduced chemical fertilizers integrated with IAA producer bacteria can positively affect the plant growth and led to decrease of chemical fertilizers application. Then optimal condition for IAA release was determined by P. mosselii and B. toyonensis. Results revealed that optimal growth medium conditions for isolates defined to be at L-tryptophan concentration of 3.0 mg mL(-1) at 96h of incubation and 32 degrees C by spectrophotometry. Increase in L-tryptophan concentration (>3.0 mg m(-1)) significantly decreased the IAA production. These results could be attributed to a possible inhibition towards the indigenous (and/or exogenous) soil microbial population by the higher concentrations of L-tryptophan. Glucose used as carbon source, gave the most IAA production (22.9 mu g mL(-1)) in E isolate. About R isolate use of sucrose in the medium culture stimulates IAA production.