Effect of L-Tryptophan and Rhizobium on Growth, Physiology, and Auxin Production of Maize (Zea mays L.)

This heavy reliance on chemical fertilizers has led to environmental problems and has prompted the adoption of sustainable practices to enhance crop production. The effect of L-tryptophan (L-TRP) and Rhizobium inoculants on the growth, physiological characteristics, indole-3-acetic acid (IAA) production and yield of maize (Zea mays L.) under controlled pot culture conditions was evaluated in this study. The experiment was conducted in a completely randomized design with six treatments and three replications, including an untreated control, Rhizobium alone, and two levels of L-TRP applied alone and with Rhizobium. Optimum concentration of L-TRP was found to be specific to each response, as at physiological maturity, the lower concentration of L-TRP in combination with Rhizobium resulted in the best shoot and root length, fresh weight of shoots and roots, and grain yield, while the higher concentration of L-TRP showed the best response for chlorophyll. IAA production was also greatest when the low concentration combined treatment was used, and combined treatments generally produced more IAA than either amendment alone, suggesting a synergistic effect between bacterial inoculation and precursor availability rather than an additive effect. There was no measurable difference in harvest index among treatments, with increased biomass accumulation being the primary driver of yield gains. These results demonstrate that the use of Rhizobium, along with an optimized concentration of L-tryptophan, can enhance the growth and yield of maize under controlled conditions, and that the effects are trait-specific, indicating the need for field testing, molecular identification of the strain, and replication in future studies.