Effect of Co-Application of Auxin-Producing Plant Growth Promoting Bacteria and Tryptophan on Wheat Growth under Water Stress Conditions

Auxin produced by plant growth-promoting bacteria (PGPR) in the wheat rhizosphere, can improve plant yield under water deficit stress condition. To investigate this issue, a completely randomized factorial design with three replications was conducted under greenhouse condition at the University of Maragheh, Eastern-Azarbayjan, Iran during 2019. Treatments were two types of growth-promoting bacteria (Bacillus simplex 40, Bacillus simplex 52); two moisture levels (50% and 80% of water holding capacity in perlite) and two levels of tryptophan (0 mg L-1 and 100 mg L-1). Under the condition of 50% of water holding capacity, the application of tryptophan without bacterial inoculation decreased wheat dry matter yield by 5%. Inoculation of Bacillus simplex 40 in the absence of tryptophan led to 25% increase in wheat dry matter yield while application of tryptophan reduced the trait by 17%. Under the stress condition, catalase enzyme activity increased by 33% and guaiacol peroxidase activity increased by 2.3% in inoculation treatments compared to control treatments. In conclusion, bacterial inoculation was able to increase wheat dry matter yield by improving the wheat antioxidant system under drought-induced oxidative stress. Furthermore, the decrease in wheat dry matter in the presence of tryptophan treatment may be attributed to probable hormonal disorders in wheat caused by high concentration of applied tryptophan.